Next Article in Journal
Preparation and Applications of Fluorinated Graphenes
Previous Article in Journal
Carbon Nanotubes Transform Soft Gellan Gum Hydrogels into Hybrid Organic–Inorganic Coatings with Excellent Cell Growth Capability
Previous Article in Special Issue
Carbon Nanohorns as Effective Nanotherapeutics in Cancer Therapy
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:

Carbon-Based Nanomaterials for Delivery of Biologicals and Therapeutics: A Cutting-Edge Technology

Institute of Pharmacy, Bundelkhand University, Jhansi 284128, India
Faculty of Medical & Paramedical Sciences, Madhyanchal Professional University, Bhopal 462044, India
Department of Chemistry, Bipin Bihari College, Jhansi 284003, India
Pharmaceutical Sciences Laboratory, Faculty of Science and Engineering, Åbo Akademi University, 20520 Turku, Finland
Authors to whom correspondence should be addressed.
Received: 31 December 2020 / Revised: 31 January 2021 / Accepted: 2 February 2021 / Published: 5 February 2021
(This article belongs to the Special Issue Functional Carbons and Carbides: Bioapplications and Beyond)


After hydrogen and oxygen, carbon is the third most abundant component present in the cosmos with excellent characteristic features of binding to itself and nearly all elements. Since ancient times, carbon-based materials such as graphite, charcoal, and carbon black have been utilized for writing and drawing materials. As these materials possess excellent chemical, mechanical, electrical, and thermal features, they have been readily engineered into carbon-based nanomaterials (CNMs) such as carbon nanotubes, graphene oxide, graphene quantum dots, nanodiamonds, fullerenes, carbon nano-onions, and so forth. These materials are now widely explored in biomedical applications. Thus, the emergence of CNMs has opened up a gateway for the detection, delivery, and treatment of a multitude of diseases. They are being actively researched for applications within tissue engineering, as vaccine vectors, and for the delivery of therapeutics to the immune system. This review focuses on the recent advances in various types of CNMs, their fabrication techniques, and their application in the delivery of therapeutics both in vitro and in vivo. The review also focuses on the toxicity concern of the CNMs and the possible remedies to tackle the toxicity issues. Concluding remarks emphasize all the CNMs discussed in the review over their possible biomedical applications, while the future perspectives section discusses the approaches to bring CNMs into the mainstream of clinical trials and their therapeutic applications.

Graphical Abstract

1. Introduction

Nanotechnology has offered to mankind various nano-enabled products or nanosystems, currently also serving various biomedical applications. These nano-constructs and assemblages with drugs, proteins, DNA/RNA, viruses, cellular lipid bilayers, cellular receptor sites, and antibodies (pivotal for immunology), are intricate in the arena of nanostructural scope [1]. Carbon-based nanomaterials (CNMs) could be considered as such a class of nanosystems, which have been explored for the delivery of therapeutics, biosensing, and bioimaging [2]. Of late, they have been pragmatic in applications such as regenerative medicine [3], cancer therapy, and theranostics [4] (Figure 1).
Carbon is one of the most interesting elements that possess extreme qualities of forming a wide range of structures with different properties. Carbon is conventionally available in allotropes [5] as “hard” diamond and “soft” graphite, where atoms are pure sp2 or sp3 hybrids organized in a hexagonal or cubic lattice; owing to the valance of carbon atoms, other allotropes such as zero-dimensional fullerenes [6] and carbon quantum dots [7], one-dimensional carbon nanotubes [8], and two-dimensional graphene sheets [9] (Figure 2 and Figure 3) have been discovered. Carbon nano-onions [10] (CNOs) are another type of CNMs that are gaining considerable academic and industrial interest for their pertinence in various biomedical extents.
Carbon nanomaterials possess specific properties such as high surface area, excellent mechanical and electrical properties that promote their application also in the therapeutic and diagnostic fields. A few of the advantages of carbon nanomaterials are summarized as follows, and Table 1 gives a brief overview of different CNMs discussed in this review with their benefits and limitations.
  • Their supramolecular π–π stacking attribute allows them to adsorb a high amount of drug.
  • As a result of their unique optical characteristics and facile amalgamation with luminous substances, CNMs can be utilized as theranostics materials.
  • CNMs possess excellent heat conversion capacity in the near-infrared region that could be well utilized for photothermal therapy.
  • Tuneable surface chemistry can be used for the controlled release of therapeutics.
Colloidal stability in the aqueous suspension of CNMs [13] is a major concern for their utilization in biomedical sectors; however, this can be tackled by activating the CNMs surface by covalent and non-covalent functionalization techniques. The functionalization of CNMs is one such unavoidable step that involves modification of the surface by introducing specific functional groups. Covalent functionalization approaches include oxidation, ozonolysis, plasma treatments, dehydrogenation, etc. [14].
CNMs have been exploited extensively in the delivery of therapeutics owing largely to the functionalization of their surface, rendering them capable of e.g., crossing biological membranes. Functionalization with appropriate targeting ligand aids in the reduction of cytotoxicity of loaded drugs toward healthy cells and augments therapeutic efficiency. The addition of small targeting molecules, e.g., folic acid [15,16] targeted against folate receptors expressed on the surface of a broad spectrum of solid tumor cells, ligands having affinity against a given receptor overexpressed on a specific tumor type [17], antibodies that identify tumor-associated antigens [18,19], and magnetic nanoparticles [16], can be associated with the drug-loaded CNMs. Via these methods, active targeting by receptor-mediated endocytosis or drug accumulation at the target site via an external magnetic field can be attained. Thus, functionalized CNMs have found applicability in the delivery of small molecules, peptides, proteins, and nucleic acids [20]. For instance, CNMs have been utilized in the delivery of anticancer agents [21], fluorescent markers for tumor detection [22], cancer phototherapy [23], theranostics [24], and so forth.
In this review, we are compiling the recent developments attained in the field of CNMs for the delivery of biologicals and therapeutics with an emphasis on carbon nanotubes, graphene oxides, graphene quantum dots, fullerenes, nanodiamonds, and carbon nano-onions as carrier materials. We have examined various CNMs employed for the treatment of different dreadful ailments and discussed the toxicity concerns along with their possible remedial approaches. Their fate for clinical use in the upcoming future has also been a focus. We expect that this review will assist researchers to focus on the possible designing of CNMs for future biomedical implementations.

2. Carbon Nanotubes

Carbon nanotubes are cylindrical large molecules that are composed of a hexagonal arrangement of sp2 hybridized carbon atoms (C–C distance of approximately 1.4 Å). The wall of CNTs comprises single or multiple layers of graphene sheets. The single-rolled sheets of graphene are termed single single-walled carbon nanotubes (SWCNTs), while multi-walled carbon nanotubes (MWCNTs) are formed by the rolling of more than one graphene sheet. Both SWCNTs and MWCNTs are capped at both ends of the tubes in a hemispherical arrangement of carbon networks known as the fullerenes warped up by the graphene sheet (Figure 4). The graphene layers of MWCNTs are separated internally by 0.34 nm on average, which constructs an individual tube of a larger outer diameter of 2.5 to 100 nm, while SWCNTs have the diameter in the range of 0.6 to 2.4 nm only. Single-walled CNTs own a well-defined wall structure in comparison to multi-walled CNTs, which have slight structural defects displaying somewhat unstable nanostructure. CNTs with their small size, high surface area to volume ratio, and ability to contain biomolecules renders them ideal candidates for the delivery of various substances [30].
Carbon nanotubes have found enormous potential due to their size (1–100 nm) which can be considered 1000 times thinner than human hair; still, they are 50 times sturdier than steel. Carbon nanotubes possess exclusive spectroscopic properties, their end and sidewalls can be easily functionalized either covalently or non-covalently, and they can be fabricated with bioactive peptides, small-molecule drugs, proteins, or nucleic acids [31]. Such agents can be easily conjugated to the nanotube through a cleavable bond. CNTs possess the potential for penetrating the cells, which enhances the cellular uptake of therapeutic agents and protects them during transportation and cellular permeation. The recent advancements made in the carbon nanotube-based delivery of various therapeutic agents are summarized in Table 2.
Drug loading to the end-capped CNTs can be attained during the synthesis or post-synthesis of the CNTs. Drug loading largely depends upon the melting point, reactiveness, surface tension, and sensitivity of the molecules to be inserted and the diameter of the CNTs. After synthesis, drug loading can be achieved by opening up the ends of the CNTs by passing electric currents through them, or by attacking the CNT with acid that corrodes the angled end parts of the tube, or by oxidization using carbon dioxide [32,33]. The most appropriate method of drug loading is the attachment of a functional group to the CNTs [34]. The functional groups can be either bonded inside or outside of the walls. Gao et al. reported that hydrophobic and van der Waals forces also play an important part in aqueous solutions during drug loading [35]. After loading, CNTs are washed using a solution that dissolves the deposits left on the outer surface [36]. Post drug loading, the caps are closed by passing a current that fuses the ends [37]. Drug loading during synthesis yields low loading efficiency of around 10% whereas, after synthesis, the drug loading percentage can reach up to 50–100% [38].

2.1. Techniques for the Fabrication of Carbon Nanotubes

Carbon nanotubes can be produced by various innovative methods such as arc discharge, laser ablation (excluding carbon black), and chemical vapor deposition methods (Figure 5). The detailed fabrication methods of CNTs have already been extensively reviewed [49,50]. Also, the types and properties of these nanomaterials can be manipulated by altering fabrication conditions such as reaction temperature, input gas concentration, or pressure [51].

2.2. Functionalization of Carbon Nanotubes

As a result of their innate hydrophobic nature, carbon nanomaterials are very difficult to disperse in the aqueous phase. Therefore, to augment their solubility and amalgamation with the biological environment [52], their surfaces are usually functionalized non-covalently with amphiphilic macromolecules such as lipids, polymers, and surfactants or covalently with hydrophilic functional groups [49,53].
Covalent functionalization: Covalent modifications can be achieved by the direct sidewall functionalization or by defect group functionalization, which involves converting or rehybridization of sp2 carbon into sp3 configurations and finally forming covalency with attacking species [54]. This is either accomplished by using halogenation, the cycloaddition of azomethine ylides, and by the addition of radicals. The defect group surface modifications are finished by engendering defects by oxidation to yield carboxylic acid functionalities, which render them the functionality to attach various targeting groups such as peptides, proteins, or antibodies by employing amidation or esterification. Double and triple covalent functionalization is used for the fabrication of multifunctional CNTs that can be utilized for drug delivery. The double covalent functionalization can be achieved either by 1,3-dipolar cycloaddition and esterification/amidation and cyclopropanation; double arylation; arylation and amidation; amidation and cyclopropanation; double 1,3-dipolar cycloaddition; 1,3-dipolar cycloaddition and arylation; etc. The triple functionalization can be accomplished by simultaneous functionalization with different aryl diazonium salts [55,56].
Non-covalent functionalization: The covalent functionalization achieved by the aforesaid modifications may lead to the loss of electrical and optical characteristics of carbon nanomaterials. Therefore, non-covalent functionalization methods were used that can avert the negative effects of the covalent modifications of CNTs. Non-covalent functionalization can be done by adsorption/wrapping biopolymers, surfactants, and polymers on the tubular surface via π–π stacking and van der Waals interactions. Polymers—for example, polyethylene glycol (PEG), poly(vinylpyrrolidone), tetraalkylammonium, poly (meta phenylene vinylene), etc.—are utilized to form a case around the single-walled carbon nanotubes when suspended in a solution of the polymer. Surfactants such as sodium dodecyl sulfate, sodium dodecylbenzene sulfonate (SDBS), Triton X-100, etc., aid in the improvement of dispersibility, solubility, and permeability through gastrointestinal tract (GIT) by adsorbing on the surface of CNTs via π interactions [57,58].

2.3. CNTs for Drug Delivery

In the early 1990s, Ijima [59] developed a new allotrope of carbon using the carbon arc discharge method and named it the “multi-walled carbon nanotubes”, which was needle-like and made up of several graphene sheets. A few years later, Prof. Ijima and Bethune established single-walled carbon nanotubes [60]. Both single and multi-walled carbon nanotubes hold exclusive mechanical, electrical, and structural properties which lends them higher forte, litheness, and electrical conductivity toward various biological entities that can be utilized for sensing, diagnosis, and drug delivery [61,62,63].
CNTs have unique electronic properties that are regulated by the quantum confinement of electrons, which propagates the electrons along the tube axis in the forward and backward direction, thus conserving energy and momentum. In addition, CNTs have a smooth density of states (DoS) and are characterized by several van Hove singularities [64]. This DoS relies on the diameter and chirality of the nanotube [65]. The conducting asset of CNT is an inverse function of its diameter; i.e., the bandgap between the valence and conduction bands decreases with an increase in diameter. At a definite point, both the bands overlap to give rise to metallic nanotubes.
Pristine CNTs are generally hydrophobic, having poor aqueous and organic solubility, and this hydrophobicity can be attributed to the size, structure, and bundling effect that restricts the uptake and assimilation in the biological environment [66]. Functionalization reduces this bundling effect that occurs due to the van der Waals forces between the adjacent nanotube surfaces, which aids in enhancing the biocompatibility and thus helps in cellular internalization and movement. Few studies reported that the functionalized nanotubes displayed improved biocompatibility with diminished in vivo and in vitro toxicity [67,68]. The extent of functionalization relies on the behavioral characteristics and reactivity of sidewall (curvature), the number of functional groups that can be attached to the sidewall, and steric hindrance between the functional groups and nanotube sidewall [69]. Drug entities can be attached to the functionalized CNTs sidewalls through covalent or non-covalent bonding.
Saikia N and Deka RC, in their studies, developed armchair (n, m) and zigzag (n, 0) SWCNTs loaded with 2-methyl heptyl isonicotinate and pyrazinamide, which were functionalized with PEG, and they investigated the structure, electronic properties, and reactivity of a series of 1,3-dipolar cycloaddition (DC) using first-principles density functional theory (DFT) calculations. The researchers reported that with an increase in sidewall functionalization, the hardness, and highest occupied molecular orbital-lowest occupied molecular orbital HOMO–LUMO energy gap decreases, which indicates a decline in the stability of the complex and localized deformation in the nanotube at the site of covalent attachment. They further reported that the solubility of pure isoniazid and pyrazinamide increased in the presence of SWCNTs. The researchers finally concluded that the optimum length and chirality of the CNTs is essential to comprehend the electronic characteristics of functionalized CNTs to understand the mechanism of the delivery of drugs [69,70].
Kang et al. tested the effect of temperature on the bovine serum albumin (BSA) release from chitosan-functionalized CNT with a thermosensitive polymer, poly-N-isopropyl acrylamide (NIPAAm) and 1-butyl-3-vinyl imidazolium (NIPAAm-co-BVIm). They reported that the release of BSA occurred just above the lower critical solution temperature of polyVBIm (38–40 °C) [71]. Functionalized CNTs lead to PEGylation, which improves constancy in the body fluids [72]. Both hydrophilic and hydrophobic drug material can be conjugated with the PEGylated CNTs either on the terminal functional groups of CNTs or to the PEG chains. Prakash Chandra et al. fabricated thermally stable, highly electrically conducting polyaniline MWCNTs (PANI/MWCNT) nanocomposites doped in two different protonic acids (i.e., hydrochloric acid and sulfuric acid) by surfactant-assisted, in situ oxidative polymerization of aniline in the incidence of potassium persulfate as oxidant. The micellar structure of the surfactant abetted the dispersion of MWCNTs along with the development of PANI/MWCNT tubular structures and provided exceptional electrical and dielectric assets for microelectronic bids [73]. Shi et al. demonstrated ibuprofen release from a hybrid hydrogel composed of sodium alginate, bacterial cellulose, and MWCNTs using an electric field [74].
A dual-responsive drug delivery system was fabricated by Seyfoori et al. for the precise delivery of doxorubicin using MWCNTs functionalized with MeFe2O4 magnetic nanoparticles, which were coated with chitosan nanogel. The pH-responsive accelerated drug release was tested on U-87 glioblastoma cells, and the result suggested higher cell mortality in a time-dependent manner [75]. Meherjuoi et al. designed silver (Ag) nanowires as a stimulator for the release of cisplatin from the interior of the various types of CNTs. They compared CNTs, silicon carbide nanotubes, and boron nitride nanotubes and reported that the drug release was fast and not dependent on the structural composition of nanotubes [76].
Gutiérrez-Hernández et al. fabricated functionalized MWCNTs in combination with bacterial cellulose as a three-dimensional (3D) scaffold for osteoblastic cell culture. They mixed the MWCNTs with innate bacterial cellulose (secreted by Glucanocetobacter xylinus) to strengthen the mechanical properties of the bacterial cellulose. It was reported that the BC-MWCNTs scaffold reinforced osteoblast viability, adhesion, and propagation at higher levels in comparison to traditional culture substrates. Finally, they concluded that the BC-MWCNTs scaffold holds the potential for bone regeneration [77].
Chemotherapeutic agents usually induce systemic toxicity, drug resistance, and experience low cellular infiltration. Chemotherapy leads to the death of cancer cells along with normal cells instigating serious side effects. Considering these hindrances, CNTs can protect the chemotherapeutics, and in turn, lower their toxicity toward normal tissues by localizing the drug at the target site [78,79]. Their interaction with lipid membranes and intracellular transport mechanism is inadequately understood, but few studies have suggested that CNTs enter cells via various endocytic processes [80,81]. During tumor progression, increased tumor vascular permeability and insufficient lymphatic drainage lead to enhanced permeability and retention (EPR effect), which allows these nanoparticles to deliver the anticancer drugs to tumor sites rather than exposing healthy cells to these, thereby reducing toxicity [82]. Table 3 provides a list of various carbon nanovectors explored in the treatment of cancer.
Many anticancer drugs have been successfully conjugated with CNTs, such as doxorubicin, flutamide, cisplatin, methotrexate, paclitaxel, etc. Chu et al. prepared integrin-binding arginine-glycine-aspartic acid (iRGD)-conjugated polyethyleneimine (PEI) functionalized MWCNT conjugated with candesartan (CD). They assembled the formulation with plasmid AT (2) (pAT(2)). They targeted avb3-integrin and AT1R of tumor endothelium and lung cancer cells with iRGD-MWCNT-CD. The anticancer drug molecule displayed synergistic downregulation of vascular endothelial growth factor VEGF upon uniting with pAT (2) and inhabited angiogenesis effectually [83]. Karimi and others fabricated multiwalled CNTs conjugated with folic acid through ethylenediamine coupling. They reported that high cancer cell death was achieved via thermal ablation induced by the CNTs. You and co-workers demonstrated the effective anticancer agent delivery to brain glioma as evident by in vitro and in vivo studies. In vitro studies were performed on rat glioma cells (C6) and human glioma cells (U87 and U251), whereas in vivo studies were conducted on mice with induced orthopedic brain glioma. From the cytotoxicity studies, they reported that the prepared complex is more cytotoxic than free oxaliplatin and suggested that functionalized MWCNTs can be a good carrier for orthotopic brain tumors. [78].
Various herbal anticancer compounds such as curcumin [84,85], paclitaxel [86], docetaxel [87], vinca alkaloids [88], camptothecin [89], quercetin [90], oridonin [91], etc., have been effectively combined with CNTs for their delivery to cancer cells. Zhao et al. also developed a multi-stimuli responsive drug delivery system for combinational chemotherapy and photothermal therapy. They fabricated mesoporous carbon nanoparticles (MCN) that displayed high loading efficiency of DOX and used them as near infrared-responsive drug carriers. Human serum albumin (HSA) was attached to the pore openings of MCN via disulfide bonds and was used as a concierge owing to its biocompatibility and apposite molecular size. The dispersity and biocompatibility of the developed system were enhanced by PEG functionalization. The drug release was pH-responsive, and in vitro studies showed laser power and concentration-dependent photothermal conversion capacity. Biodistribution studies exhibited prolonged retardation of DOX at tumor sites. In vivo antitumor studies revealed that MCN/DOX with NIR irradiation displayed the highest tumor inhibition rate against 4T1 tumors in mice. They concluded that the fabricated MCN/DOX system could be discovered as a multi-responsive drug release platform for combinable photothermochemotherapy [92]. Mehra and Jain prepared DOX-loaded folic acid and estrone-anchored PEG functionalized MWCNTs for the targeted release of drug. They reported the expanded survival period of the experimental model in comparison to the animals treated with free drugs [93].

2.4. CNTs for Vaccine Delivery

A vaccine must instigate a potent immune response at the cellular or humoral level. At the cellular level, it excites cytotoxic T cells, which mark and abolish infected cells, whereas, at the humoral level, vaccines rouse the making of counteracting antibodies which helps opsonization and following pathogen removal. For diseases such as HIV or malaria, vaccines need both cellular and humoral responses for the deterrence of infection and the abolition of circulating pathogens [94]. The immune system (innate and adaptive) comprises a collection of cells that circulates within the body as well as resides at the site of entry points such as skin, respiratory, gastrointestinal, and genital tracts, waiting to counter invading pathogens. The innate immune cells such as macrophages and neutrophils identify pathogens instantly and abolish them through the activation of different antibacterial effector functions. T and B cells are crucial for the instigation of the cell-mediated and humoral immune system. T cells with CD4+ helper T cells stash various cytokines to control the functions of B cells, whereas CD8+ T cells identify and terminate virus-infected cells [95].
Vaccine delivery faces many issues such as inappropriate absorption, the probability of antigen-caused hypersensitivity, anaphylactic responses, and adjuvant vaccine aversion. A lot of new tactics have been tested to boost vaccine delivery and owing to the adjuvant action, CNTs have also been implied for vaccine delivery to improve the action of the vaccine. The structure of SWCNTs is 100% surface atoms and thus, they allow the conjugation of various antigens onto their surface. The delivery of vaccines/antigens can be promoted by the engulfment of the system by phagocytic cells, inducing an immune response [96].
Various types of immune cells such as macrophages, monocytes, natural killer cells (NK), dendritic cells, T and B cells are known to uptake CNTs [97]. At the same time, CNTs did not hamper the health of these cells, due to their non-toxic nature [98]. It is imperative to modify the surface of the single or multiwalled CNTs for the induction of diverse reactive moieties which later can be utilized for the addition of antigenic peptides and proteins as well as vaccines. Chemical modification of the CNTs renders a high dispersion of vaccines, thereby enhancing the performance of the antigen in terms of their pharmacokinetic and pharmacodynamic behavior [5]. Yang and co-workers demonstrated that MWCNTs and tumor lysate protein (tumor cell vaccine) conjugate specifically enhanced the efficacy of antitumor immunotherapy in a mouse model bearing the H22 liver tumor [99].
The characteristic feature of CNTs to link various antigens or immune stimulants, which enables them to be attached to bacterial, viral, and protozoal antigens. Pescatori et al. demonstrated a microarray profiling of THP-1 (a monocytic cell line) with both functionalized and non-functionalized CNTs, which activated several genes involved in monocyte response to infection or vaccination such as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α (TNF-α), along with others [97].

2.5. CNTs for Gene Delivery

The introduction of nucleic acids has created great curiosity in disease treatment to regulate, repair, restore, add, and/or seize a specific genetic site essential for disease indication. Gene therapy may well be utilized for the delivery of nucleic acids either through viral or non-viral vectors. Viral vectors have shown raised efficacies in transfection, but their clinical application is stalled by the glitches of immunogenicity and oncogenicity, lack of cell targeting potential, and low genetic payload [100]. Non-viral vectors possess an upper hand over viral vectors, as they are safe, can deliver genes, and they are reasonably inexpensive. Several non-viral vectors (gene carriers) including nanoparticles, peptides, dendrimers, liposomes, carbon nanotubes, etc. have been investigated for gene delivery [101]. CNTs have been widely utilized for the delivery of nucleic acids. The chemical modification of pristine CNTs (single or multi-walled CNTs) for example, aminated or carboxylated or strengthened CNTs using the proton-rich polymer polyethyleneimine (PEI) offers them litheness for gene therapy. SWNTs or MWNTs offer benefits of effectual surface modification for the designing of nanovectors for effective gene therapy. Varkouhi and his group investigated two cationically functionalized (CNT-PEI and CNT-pyridinium) CNTs for siRNA delivery. They reported that both functionalized CNT-complexed siRNAs showed 10–30% silencing activity and reduced cytotoxicity against H1299 cells. They stated that the type of functionalization of CNTs resulted in a non-cytotoxic CNT-based delivery system [102]. Tan et al. non-covalently functionalized SWCNTs with PL-PEG-NH or PL-PEG-maleimide. They further conjugated the functionalized SWCNTs with a 5′-thiolated siRNA against GFP (siGFP) and RFP (siRFP). They evaluated the silencing of GFP and RFP expression by SWCNT–siRNA via fluorescence spectroscopy and reported a 50–80% GFP expression knockdown in H1299, HeLa, MCF-7, and 293T cells by SWCNT-siGFP. They also observed gene silencing despite incubation with inhibitors on different cellular internalization pathways. The SWCNT–siRNA showed successful knockdown of GFP expression in different cell lines, indicating the release of siRNA into the cytoplasm, which silenced the gene expression.

3. Graphene/Graphene Oxide/Reduced Graphene Oxide

Graphene and its derivatives are the material of thoughtful consideration because of its inimitable inherent assets such as highly interesting photoluminescence properties as well as easy surface functionalization, which leads to its applicability in various biological settings [114]. The large surface area, chemical purity, and free π-electrons lend graphene a suitable candidate for the delivery of therapeutics [115], whereby conjugation strategies can enhance the biocompatibility and residence time in vivo [116]. These materials have been explored for the delivery of chemotherapeutic agents [117], genes [118], peptides [119], and tissue engineering [120]. Hummers (1958) developed graphene oxide by the vigorous oxidation of graphite [121]. A schematic illustration of their use is given in Figure 6. Graphene oxide possesses unique structural features such as large and planar sp2 hybridization of carbon, high surface area, and augmented oxygen-containing groups. Oxygen groups offer biocompatibility, physiological solubility, and stability to GO, and the high payload of drugs/genes via chemical conjugation or physisorption tactics can be achieved. Graphene oxide used for drug delivery is generally one to three layers thick with a size ranging from a few nanometers to several hundred nanometers [122].

3.1. Techniques for the Fabrication of Graphene

Graphene can be synthesized using two methods: i.e., bottom-up and top-down synthesis methods. The synthesis methods lend excellent properties to these materials. The interaction between therapeutics and graphene-based materials depends on their properties such as layer number, lateral dimension, chemical residual, surface charge, and surface functional groups.
Bottom-Up Synthesis: This method includes three procedures: (i) epitaxial growth on silicon carbide; (ii) the chemical vapor deposition method (CVD); and (iii) the plasma-enhanced chemical vapor deposition (PECVD) method. The first method [124] uses the thermal decomposition of silicon carbide at high temperatures under vacuum or in inert gas. As carbon has negligible vapor pressure in comparison to silicon, graphene layers are formed on the silicon carbide surface after silicon sublimation. Large surface area graphene can be produced by the CVD method. In this method, a precursor gas (e.g., methane, acetylene, ethylene, propene) containing hydrocarbon molecules are charged into the reactor, in which the hydrocarbon molecules are catalytically decomposed into carbon radicals and arranged into graphene structures on the catalytic layer of the substrate (Ni, Cu, Rh, Co, or alloys). The properties of the fabricated graphene such as layer number, crystal size, and layer number are largely affected by several factors such as precursors, assistant gases, catalyst layer, and temperature. PECVD shows an advantage over CVD in the synthesis of graphene at a relatively low temperature with reduced deposition time. It also resolves the evaporation problem of a catalyst layer at high temperatures.
Top-Down Synthesis: This method helps in the segregation of graphene sheets from high-quality graphite, which contains stacked multi-layer graphene using a mechanical or chemical method. It involves mechanical and chemical exfoliation methods and the GO reduction method. The mechanical exfoliation method is used to separate graphene from graphite using a scotch adhesive tape to break the van der Waals force between the layers of graphite by a repeated sticking and lifting process [9], producing high-quality graphene, but it lacks large-scale production ability. On a large scale, graphene can be fabricated using the reduction of graphene (rGO) method. This method involves GO production and GO reduction to rGO by the method described by Hummers [121]. The oxidation process involves the reaction of graphite with sodium nitrate, concentrated sulfuric acid, and potassium permanganate, which introduces oxygen-containing functional groups onto graphite sheets. The graphene oxide layer can be separated by ultrasonication in a polar solvent, e.g., water because of the introduction of enlarged layer space due to the insertion of functional groups.

3.2. Functionalization of Graphene

For their biomedical use, graphene-based materials should be functionalized for the same reasons mentioned above for CNTs. This can be achieved for instance via PEGylation [125] or coating with dextran [126], both of which decrease their toxicity and augment their biocompatibility. Surface functionalization can be achieved by non-covalent and covalent binding.
Non-Covalent Functionalization: This method involves forces such as hydrophobic interactions, π–π stacking, or electrostatic binding between the graphene-based materials and the active molecules. The hydrophobic interactions are utilized to absorb the aliphatic parts of surfactants onto the graphene by the interaction of polar parts of surfactants [127], thus enhancing the stability of surfactant-functionalized graphene or rGO in polar solvents. Electrostatic interactions can also be used for the functionalization of these materials, since GO sheets are negatively charged, and consequently, a positively charged biomolecule can be electrostatically adsorbed to the surface of the GO surface [128,129]. The same strategy can also be used to flexibly modify the GO surface with polymers and targeting ligands [130].
Covalent functionalization: The functional groups such as the carboxyl, epoxy, and hydroxyl groups on the GO can be used for covalent functionalization. Similarly, the carboxylic acid group of GO can be utilized for the amidation reaction with the amine group in polymers [131]. PEI functionalization was achieved on poly(acrylic acid) modified GO upon the reaction of ethyl(dimethylaminopropyl) carbodiimide/N-hydroxy succinimide EDC/NHS with the carboxylic acid group. This covalent functionalization augmented the in vitro proliferation and focal adhesions in hMSCs of the GO–PEI nanocomposites [132]. Due to its highly cationic charge density, PEI can also be electrostatically adsorbed to the GO surface (as outlined above) and thus serve as a versatile platform for further functionalization based on amine chemistry [130].

3.3. Graphene Oxide for Drug Delivery

Several hydrophobic drugs, for example, doxorubicin and docetaxel, can be adsorbed onto graphene using simple physisorption via π–π stacking, along with antibodies for the selective targeting to cancer cells. π–π stacking and electrostatic or hydrophobic interactions of graphene provide a high carrying capacity of poorly soluble drugs deprived of conceding drug strength. Table 4 summarizes the application of GO-based drug delivery.
Boran et al. conjugated graphene oxide with zoledronic acid (ZOL-GO) and evaluated these in vitro on cells. They explored the allied morphological changes of bone marrow-derived mesenchymal stem cells (BM-MSC) and MCF-7 breast cancer cells along with the effect of the drug on the mineralization of BM-MSCs. They reported that the nanostructured ZOL-GO facilitated the mineralization of BM-MSC cells, which was demonstrated by the formation of clusters around the cells. The Boran group concluded that the ZOL-GO nanostructures can be a promising drug complex for the treatment of osteoporosis and metastasis [133].
Islami et al. constructed efficient quercetin-loaded single-layer graphene oxide (GO) sheets grafted with hyperbranched polyglycerol (HPG) on the surface of GO through the ring-opening hyperbranched polymerization of glycidol. The fabrication was carried out using both a modified and improved Hummers method. HPG improved the stability of GO sheets in biological fluids with augmented drug-loading capacity and high encapsulation efficiency. HPG-GO displayed the controlled and sustained release of quercetin and suggested that an acidic pH could aid in the drug release. Moreover, the HPG-GO did not exhibit cytotoxicity on the MCF-7 cell line in diverse concentrations during 72 h incubation [134].
Yang et al. developed a magnetic and bio dual targeting GO–Fe nanoparticle hybrid. From the in vitro experiments, they demonstrated that the drug delivery cargo not only enhanced the anticancer outcome but can also provide site-specific targeting of the SK3 human breast cancer cells by the magnetic field guided GO–Fe nanoparticles. Yu et al. designed an α, β6-targeting peptide (HK-peptide) functionalized and photosensitizer (HPPH)-coated graphene oxide (GO (HPPH)-PEG-HK), which triggered the dendritic cells and expressively barred the tumor growth and lung metastasis by increasing the intrusion of cytotoxic CD8+ T lymphocytes in the interiors of the tumors as evinced by in vivo optical and single-photon emission computed tomography [135].
The Cheon group fabricated a doxorubicin-loaded BSA functionalized graphene sheet for combinational chemo- and photothermal therapy in brain tumors [136]. Fong et al. developed hyaluronic acid-chitosan-g-poly (N-isopropyl acrylamide) grafted DOX-folic acid-GO thermosensitive hydrogel for breast cancer therapy [137]. Shao et al. fabricated a mesoporous silica-nanoparticles coated with polydopamine functionalized with rGO, followed by modification with hyaluronic acid and loaded with DOX. The developed system was pH-dependent, which triggered the release of the chemotherapeutic agent and proved to be an effective carrier for cancer therapy [138].

3.4. Graphene Oxide for Gene Delivery

Graphene-mediated gene delivery has emerged as a novel technique where graphene derivatives have shown tremendous potential for gene transfection. However, it is essential to modify graphene derivatives with polymers to render them with cationic surface properties, which facilitate electrostatic interactions with anionic oligonucleotides. To date, PEI and poly(sodium 4-styrenesulfonates) have been well thought out for gene delivery via graphene derivatives [139,140,141].
Zhang et al. observed the use of PEI-conjugated GO to deliver DOX and siRNA. They demonstrated that the conjugate not only enhanced the therapeutic efficiency but also led to an increment in safety [142]. Similarly, Feng et al. explored the effects of PEI (1.2 kDa and 10 kDa) on the cytotoxicity of PEI-GO [129]. Cao and the group reported the role of lactosylated chitosan oligosaccharide LCO-functionalized GO in the removal of toxicity and the enhancement of loading efficiency of fluorescein amidites (FAM)-DNA to human hepatic carcinoma cells (QGY-7703) [143]. Liu and his group fabricated a graphene-based gene vector by employing graphene-oleate-polyamidoamine (PAMAM) dendrimer hybrids owing to the high dispersion and stability of graphene in water solutions. The hybrid was developed by using oleic acid and covalent binding of PAMAM dendrimers. The group investigated the plasmid DNA transfection capacity and its cytotoxicity toward HeLa and MG-63 cells. They reported that the developed hybrid was biocompatible to HeLa cells, and the cell viability retains about 80%, although the hybrid was cytotoxic to MG-63 cells at concentrations above 20 mg/mL [144].

4. Graphene Quantum Dots (GQDs)

Graphene quantum dots (GQDs) have found their place recently as the newest member of the carbon nanomaterial family. GQDs comprise a few layers of graphene, and its functional group has a lattice distance of about 0.24 nm with sp2 hybridization, which is somewhat similar to a small flake of graphene. They can be differentiated from carbon quantum dots (CQDs), which possess a lattice distance of about 0.34 nm, and further, CQDs are amorphous with sp3 hybridization. GQDs possess characteristic photoluminescence owing to quantum confinement. Also, GQDs hold the same features as graphenes such as large surface area and free π-electrons availability, which lends them suitable for imaging, sensing, cancer therapy, etc. [153,154,155].

GQDs for Drug Delivery

The oxygen-rich surface of the GQDs is the key feature that makes them suitable for drug adsorption and enhancing colloidal stability in vivo, along with the features of a single atomic layer and small size. The fluorescent characteristics of graphene quantum dots render them traceable when targeted to e.g., cancer cells [156]. Tian et al. developed a framework of zeolite imidazolate (ZIF-8)-embedded DOX-loaded GQDs, which showed an acidic pH-responsive drug release behavior [157]. Zheng et al. demonstrated intracellular drug delivery and real-time drug release from DOX-loaded aptamer/GQD-capped fluorescent mesoporous silica nanoparticles. Under the extracellular conditions, the fluorescence of the fluorescent mesoporous silica nanoparticles (MSNs) remains off at a low ATP level. When the nanocarrier is recognized and internalized into the target tumor cells by an AS1411 aptamer, in the ATP-rich cytoplasm, the ATP aptamer causes the shedding of the GQDs from the nanocarriers, thus resulting in drug release and at the same time, the fluorescence of MSNs provides real-time imaging possibility [158].
The Wei group developed DOX-loaded GQDs and conjugated them with Cy5.5 dye via a cathepsin D-responsive (P) peptide, which augmented tissue penetration and cellular uptake of the drug. The cell uptake in 4T1 cells and the drug release was monitored by confocal laser scanning microscopy. The GQDs-treated cells displayed blue fluorescence, exhibiting the internalization of the developed formulation. They reported superior therapeutic performance both in vitro and in vivo due to the enhanced tissue penetration and cellular uptake. The developed system served as probes for programmed tracking of the drug delivery and release process, as well as drug-induced cancer cell apoptosis via the GQDs, doxorubicin, and Cys fluorescence. The Nigam group fabricated a GQD-conjugated gemcitabine-loaded HAS nanoformulation for the targeted delivery of the drug to the tumor cells with the help of albumin via the gp60 pathway [159].

5. Fullerenes

Buckyball clusters or buckyballs, also known as endohedral fullerenes, include fullerenes, buckminsterfullerene, and C60, which are composed of fewer than 300 carbon atoms. Fullerenes possess numerous functional points that permit the attachment of chemical groups of targeting ligands in three-dimensional orientations, which could facilitate cellular targeting. It is also possible to modify their allotropes to optimize pharmacokinetic characteristics, therapeutic effects, and other attributes such as size, hydrophilicity, and colloidal stability in a biological environment.

5.1. Techniques for the Fabrication of Fullerenes

Fullerenes can be synthesized via the pyrolysis of polycyclic aromatic hydrocarbon as naphthalene, corannulene, or higher polycyclic compounds. These compounds are decomposed at high temperatures (around 1000 °C) with the cleavage of hydrogen bonds and production of mainly C60 and C70, in the presence of an inert gas (argon). Fullerenes can also be fabricated by an arc-discharge method between two graphite electrodes by applying high voltage. The discharge induces vaporization of the graphite with the formation of plasma. Fullerenes are synthesized by condensation of the graphite plasma in particles that get deposited onto the reactor walls [160].

5.2. Functionalization of Fullerenes

Fullerenes are functionalized to overcome the problems of poor water solubility and low solubility in several organic solvents [161]. Their surface can be functionalized by the use of solubilizing agent complexation to partially mask the surface of the fullerenes and by covalent functionalization [162]. The presence of double bonds in the fullerene structure lends them to be modified greatly by functional groups of choice [163,164]. Fullerenes are comprised of carbon of erratic size and molecules that look like a hollow sphere or tube. They are composed exclusively of carbon in varying sizes resembling a hollow sphere, ellipsoid, or tube [6] with a strong apolar character that enables them to develop into lipid-like systems that can easily cross biological membranes [165].

5.3. Fullerenes for Drug Delivery

Zhao’s group prepared a fullerene-based (C82) DOX-loaded, cyclic RGD (DOX-C82-cRGD) complex for lung cancer treatment that possessed probable clinical effectiveness [166]. Hazrati and co-workers constructed a C30B15N15 heterofullerene carrier system by employing the density functional theory for the delivery of isoniazid. They reported that the interaction of the -NH2 group of isoniazid with the boron atom of the fullerene engendered a high amount of energy, which altered the fluorescence emanation of the C30B15N15 that caused the parting of isoniazid from the surface of the carrier by proton attack at a low pH of cancerous tissues [167].
Tan and co-workers fabricated a biocompatible and water-soluble fluorescent fullerene (C60-TEG-COOH)-coated mesoporous silica nanoparticle, which delivered the DOX in a pH-responsive manner, and the cellular uptake of nanoparticles was detected via the green fluorescent property of the C60 [168]. Fullerenes have also found their application in the delivery of anti-inflammatory agents. Recently, C60 fullerenes have been recognized to persuade the suppression of Ag-driven type-I hypersensitivity through the prominent prevention of an IgE-dependent mediator. Hence, they can manage the mixt mast-cell-dependent allergic inflammations, asthma, inflammatory arthritis, heart diseases, and multiple sclerosis [169]. Also, fullerenes exhibit anti-inflammatory properties by stabilizing mast cells and peripheral blood basophils and inhibiting the release of proinflammatory mediators [170].

5.4. Fullerenes for Antibody/Antiviral Delivery

Fullerenes due to their excellent surface structural properties have also been utilized in the delivery of antibodies. Ashcroft and co-workers successfully conjugated antibodies to fullerenes by using a novel water-soluble C60 derivative as the fullerene scaffold. The scaffold was modified through the Bingel–Hirshc reaction and an antibody ZME-018 was covalently attached through the disulfide bridge exchange. ZME-018 explicitly targets the gp240 antigen present in over 80% of the human melanoma cells [171]. Fullerenes were also functionalized to produce a photoactive stage for the distant deactivation of viruses and bacteria. Kim and his group fabricated a substratum of hot-pressed silica particles placed on a metallic substrate functionalized with 3-aminopropyltrietoxysilane and amine groups to covalently couple the fullerenes. The research group studied the inactivation of the MS2 bacteriophage at predefined distances from the irradiated surface and reported disinfection of the bacteria and virus by the immobilized C60 in the gas phase via photosensitization, contrary to singlet oxygen (1O2), which was effective up to around 10–15 cm from the surface [172].

6. Nanodiamonds

Nanodiamonds (NDs) are the newest exposed allotropes of carbon with a large surface area and a single crystal size of 2–8 nm. NDs are mostly created by the detonation process [173] and chemical vapor deposition methods [174]. They are nanocrystals with tetrahedral carbon atoms in a 3D cubic trellis owning a diamond-shaped structure with electrical properties of diamond, coated with an onion-like graphite shell. Their surface comprises functional groups formed on the ND surface after purification stemming from the residual (non-diamond) carbon as a result of the detonation process, usually containing oxygen, such as hydroxyl, carboxylic acid, ketone, lactone, and ether. NDs with nitrogen vacancies in their center, thus exhibiting photoluminescence characteristics are termed fluorescent NDs (FNDs) and have found highly interesting applications in bioimaging [175,176,177].
The ND physicochemical properties such as size and surface chemistry are highly decisive for their fluorescence properties [178]. NDs are very seldom present as single crystals in solution, the aggregates of which determine their size during application. Nevertheless, these aggregates are often hydrophilic due to the functional groups and can thus still form a stable aqueous colloidal suspension [179,180], which is imperative for their biomedical applicability. Due to this property, NDs have also been proposed as drug carriers, whereby the large surface area is exploited for adsorbing or linking numerous drug moieties on the surface of the NDs by covalent and non-covalent functionalization methods [181]. However, given the diversity of the ND surface owing to the production method, the precise surface chemistry of ND is challenging to control and define. Another widely employed strategy to make use of the intrinsic photoluminescent properties of ND while increasing their drug-carrying capacity is by coating the ND with shells of other materials that can harbor drug molecules in much higher amounts than what can be adsorbed onto the native ND surface or otherwise improve their biomedical applicability [182,183,184]. The drug adsorption onto native nanodiamonds depends on parameters such as maximal monolayer capacity, binding strength, and the degree of drug removal from the solution. The various applications and advantages of NDs are illustrated in Figure 7.

Nanodiamonds for the Delivery of Therapeutics

The Li group successfully treated the immunosuppression associated with glioblastoma with DOX–polyglycerol–ND composites. They developed cellular and animal GBM models by THP-1 derived dendritic cell and female athymic Balb/c nude mice correspondingly. The group reported that the nanocomposite could rouse the immunogenicity of glioblastoma cells both in vivo and in vitro, by persuading autophagy and emanating antigens from the glioblastoma cells [15]. Roy et al. formulated -COOH functionalized and -NH2 functionalized NDs loaded via monolayer surface adsorption with efavirenz. They revealed that the bioavailability of the efavirenz was augmented, and non-functionalized NDs possessed higher drug-loading capacity than the functionalized NDs. They demonstrated that the functionalized NDs can infiltrate the blood-brain barrier and release the drug in the central nervous system using an in vitro BBB model of primary human brain microvascular endothelial cells and astrocytes. Neural stem cells can multiply and segregate into astrocytes, neurons, and oligodendrocytes. This differentiation of neural cells can be helpful in the treatment of neurodegenerative diseases such as Alzheimer’s and Parkinson’s [185].
Nanodiamonds can boost neural stem cell adhesion and differentiation. In a trial, Taylor et al. demonstrated that the NDs supports rodent neuronal outgrowth. They inspected the interaction of human neural stem cells with the NDs [186]. Edgington and Jackman nurtured human neural stem cells with oxygen and hydrogen functionalized monolayers of NDs and evaluated neural stem cell adhesion and proliferation for seven days and stated that the adhesion and proliferation were higher with oxygen functionalized NDs than the hydrogen functionalized NDs. It was reported that the NDs monolayers can provide comparable physicochemical characteristics of extracellular matrix protein. Their report suggested that the NDs can be a substratum for neuronal growth and be a possible applicant in neurodegenerative brain disorders [187].

7. Carbon Nano-Onions

Carbon nano-onions (CNOs) are zero-dimensional carbon nanoparticles that are categorized by their multi-layered closed shells all-encompassing one another, similar to that of an onion. These CNOs possess a diameter in the range of 1.4 to 50 nm with an interlayer distance of approximately 3.4 Å with a C60 or C80 fullerene at their core (Figure 8) [188]. Structural and dimensional variations are bound and vast depending on the method of preparation [189]. CNOs can be fabricated through various techniques, which results in the production of CNOs of various shapes and sizes. DC arc discharge [10], electron beam irradiation [190], underwater arc discharge [191], thermal annealing under high vacuum [192], thermal annealing under helium environment [193], catalyst-free synthesis through thermolysis under Ar or air environment [194], and thermal reduction are the methods that can be used for the production of CNOs with tunable sizes and shapes.
Pristine carbon nano-onions (p-CNOs) developed through the above-mentioned methods are hydrophobic, which leads to their aggregation in aqueous and organic solvents, even after sonication. Their solubility and dispersibility can be amended via covalent and non-covalent surface modification [196]. The covalent functionalization of CNOs particularly by oxidation renders them with augmented water dispersibility, extending the possibility of amidation and esterification reactions of the carbon nano-onions. CNOs can be functionalized by non-covalent interactions via electrostatic interactions, van der Waal forces, and π interactions.

Carbon Nano-Onions for Therapeutics Delivery

Utilizing the functionalization of the CNOs, their application in various biomedical sections such as drug delivery, tissue engineering, bioimaging, sensing, CNOs as a drug for cancer, and CNS-related disorders have been vastly explored (Figure 9, Table 5). The supramolecular functionalization of CNOs via stimuli-responsive biocompatible polymers enables them to be an effective targeted drug delivery system. Narsimha and co-workers engineered 4-hydroxyphenyl methacrylate-carbon nano-onions (PHPMA-CNOs = f-CNOs) embedded bovine serum albumin (BSA) nanocomposite fibers by Forcespinning® (FS) technology for stimuli-responsive delivery of DOX. The group reported a slow and prolonged DOX release over a 15-day study along with augmented thermal properties and in vitro degradation. They tested the cytotoxicity of hydrogels with osteoblast cells that displayed good cell viability and cell growth. The developed system exhibited a pH-responsive sustained drug release over 15 days, which suggested that zein/f-CNOs hydrogel could be a potential drug delivery system for the colon [197].
D’Amora et al. functionalized CNOs non-covalently with hyaluronic acid-phospholipid (HA-DMPE) and successfully targeted CD44 overexpressed cancer cells. Functionalization augmented the solubility of the nanoconstruct, enhanced the in vitro cell toxicity in human breast carcinoma cells overexpressing CD44, and increased the uptake in comparison to human ovarian carcinoma cells with an imperceptible amount of CD44. They reported that the CNOs composite possessed high in vivo biocompatibility in zebrafish (Danio rerio) during the different stages of development and established CNOs localization in the digestive tract of the zebrafish larvae [198].
Carbon nano-onion/surfactant (CNO/surfactant) composites facilitate the manufacturing of soluble nanostructures by utilizing the hydrophilic attribute of surfactants and robustness of carbon structures in the fabrication of CNO/surfactant composites with enhanced solubility and other physicochemical properties. Bobrowska et al. employed hexadecyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), Triton X-100, and Tween 20 to functionalize the CNOs by the non-covalent technique. This method produced a stable, well-dispersed CNO/surfactant nanocomposite structure that was evaluated for its in vitro biological activity against E. coli. Their study revealed that only the CNO/CTAB composite decreased the cell viability in vitro. They further reported that this activity could be allocated to the simple composite dissociation in water solutions, although antimicrobial assets of the composites are better to some extent in comparison to pure CTAB, indicating a synergistic effect of the CNO/surfactant nanocomposite when compared to pure surfactant [199].
Babar and co-workers reported an interaction between calf-thymus (CT) double-stranded DNA (dsDNA) and water-soluble carbon nano-onion (wsCNO) in water that followed denaturation of dsDNA (double-stranded DNA) to ssDNA (single-stranded DNA). The ssDNA concomitantly wrapped with the spiked surface of wsCNO and created a triangular aggregate confirmed by SEM images, which further aggregated to form a six-petal flowery arrangement hexagonally and reached a dead-end network as evident by SEM and optical fluorescence microscopy. This dead-end network aggregate lacked the intrinsic optical property of DNA and displayed a loss of its activity (Figure 10). The researchers finally concluded that the wsCNO being non-toxic can be explored to control the unwanted proliferation of rouged DNA by interacting with wsCNO, which can be utilized for the prevention of such viral DNA replication in recognized diseases [200].
Tripathi et al. developed graphitic photoluminescent water-soluble carbon nano-onions (wsCNO) from the traditional pyrolysis of vegetable ghee without employing any metal catalyst through a simple oxidative treatment using nitric acid. The fabricated wsCNO possessed tunable photoluminescence behavior from the visible-to-near infrared region. They further segregated small-sized wsCNO from the bulk via gel filtration acquired a highly fluorescent colored fraction, which they used for cell imaging of E. coli and Pseudomonas putida and the selective, immediate detection of glucose molecules based upon a simple fluorescence “turn-off”/”turn-on” technique [201]. Pakhira and co-researchers demonstrated the successful crossing of small-sized wsCNO through the blood-brain barrier in the murine model of Cerebral Autosomal-Dominant Arteriopathy with Subcortical infarcts and Leukoencephalopathy (CADASIL) as well as in Glioblastoma Multiforme (GBM)-induced mice. They reported that the drug was readily eliminated from the animal model after a few days, signifying the probable use of water-soluble carbon nano-onions as a drug carrier [202].

8. Toxicity Concerns for Carbon-Based Nanomaterials

There have been a lot of concerns on the safety issues of the biomedical applications of CNMs. Many of the toxicity and long-term effect concerns are related to the persistence of CNMs in biological systems. A series of information on the pharmacokinetics, metabolism, long duration of CNMs in vivo, and toxicity is required. Several studies have been conducted reflecting the conflicting outcomes over the toxicity of CNMs, concerning their successful biomedical application [208,209,210,211,212]. It has been demonstrated that concentration, lateral dimension, surface properties, types, and presence of functional groups markedly affect their toxicity in the biological environment (Figure 11) [213,214].
The physical characteristics of CNTs such as fiber shape, length, and accumulation could affect the immunological responses and their accretion in tissues [215]. Shorter CNTs were reported to be less toxic than longer CNTs when injected subcutaneously. Shorter CNTs were found in the cytosol of the macrophage after 4 weeks, but longer CNTs were found to be free-floating and caused inflammation. This study confirmed that the toxicity of MWCNTs was length-dependent and was comparable with that of asbestos toxicity.
Wang et al. exhibited a cell mapping curve for various cells under similar conditions and stated that the GQDs having a size below 10 nm possess high cell viability [216]. There are reports that the solubilizing agents also impacted the toxicity of CNTs [217,218]. Jos et al. reported that –COOH-functionalized SWCNTs induced greater toxicity in the human umbilical vein endothelial cell (HUVEC) cell lines in comparison to the non-functionalized SWCNTs [219]. Metallic impurities such as metal ions incorporated during fabrication contribute a lot to the toxicity of CNTs [220,221]. Graphene also has toxicity concerns that restrict its use in the biomedical field, and to lower it, coating with blood protein has been demonstrated by the Chong group [222]. GQDs with smaller size seems to be less toxic than GO or CNT. Tian and the group reported that hydroxylated GQDs showed substantial toxicity on A549 and H1299 cells [223]. Simultaneously, a study conducted by Nurunnabi et al. stated that carboxylated GQDs showed no acute toxicity on KB, MDA-MB231, A549, and normal cells such as MDCK [224]. They further reported in their in vivo studies that the GQDs did not affect the organs notably in long-term studies.
Garriga et al. reported the cytotoxicity of the various carbon nanomaterials in their study. They developed multiple CNMs such as carbon nanohorns (CNH), carbon nanotubes (CNT), carbon nanoplatelets (CNP), graphene oxide (GO), reduced graphene oxide (GP), and nanodiamonds (ND). They tested the in vitro cytotoxicity of the above-mentioned CNMs by the MTT assay in human epithelial colorectal adenocarcinoma (Caco-2) cells and human breast adenocarcinoma (MCF-7) cells. The cell viability was found to be in the following order: CNP < CNH < RGO < CNT < GO < ND for both Caco-2 and MCF-7 cell lines. They reported that ND and GO showed low toxicity owing to the presence of oxygenated functional groups on their surface, which guards their hydrophobic domains. On the other hand, carbon nanohorns and carbon nanoplatelets induced Caco-2 and MCF-7 apoptosis/necrosis and increased ROS levels, which could be associated with the lowering of cell viability in comparison to carbon nanotubes and reduced graphene oxide [225]. Graphene has been evaluated for its toxicity in animals and cells [226]. A range of animal models has also been utilized in the investigation of e.g., ND biocompatibility and fate in vivo [227]. Various in vitro and in vivo studies have been reported to assess the cell viability, gene activity, and physiological behavior of the CNMs [228,229,230,231,232]. In a study on mice, nanodiamonds when administered within the trachea exhibited low pulmonary toxicity. The amount of nanodiamonds decreased with time in the alveolar region, and the macrophages laden with nanodiamonds stayed in the bronchia for 28 days after exposure [230].
Toxicity issues of CNMs on humans are still not assessed. Few studies have indicated that pristine CNTs, similarly to asbestos, could be the possible source of lung disease in industrial workers [233,234].
Ali-Boucetta et al., in their studies, reported that the asbestos-like reactivity and pathogenicity reported for long, pristine nanotubes can be reduced completely by surface modification and curtailing their length upon reacting with chemicals such as tri(ethylene glycol) (TEG) [235].
By the functionalization of CNMs, toxicity can be lowered for their biomedical applications. Rungrotmongkol et al., in their studies, indicated that non-covalently functionalized chitosan-coated CNTs accumulated in the reticuloendothelial system (RES) and were slowly excreted through the bile without causing side effects to the mice. The so fabricated CNTs displayed improved dispersion and biocompatibility [236]. Similarly, Kam and the group non-covalently functionalized SWCNTs with amphiphilic phospholipid-polyethylene glycol (PLPEG). The developed system exhibited augmented solubility, biocompatibility, and stability in the aqueous phase, as the hydrophobic lipid chains of PLPEG were strongly adsorbed onto the CNTs surface, while the hydrophilic PEG chain enhanced the solubility and biocompatibility of the entire functionalized SWCNTs [237].
Russier et al., in their recent study on myelomonocytic leukemia, reported that few layers graphenes (FLG) dispersions can attack monocytes, being non-toxic to the immune cells. They demonstrated that graphene holds targeting ability and boosted the necrosis of monocytic cancer cells. They further compared the FLG and etoposide chemotherapeutic potential where FLG showed substantial anticancer activity [238].

9. Conclusions

The current market showcases more than 50 nanomedicine-based drug products that are positively affecting the health of humans, and there are hundreds of clinical trials that are ongoing for the treatment of ailments such as cancer, rheumatoid arthritis, inflammatory bowel diseases, and diabetes [239]. Therefore, nanomedicine could be the frontier that could systematically curtail all the toxicity issues to utilize CNMs’ potential in biomedical applications.
Carbon-based nanomaterials have established themselves as promising materials within nanomedicine, having found applicability in the potential treatment of many ailments such as cancer, genetic disorders, and the allowed inventive delivery of bioactive. CNTs (single and multiwalled) have displayed excellent carrier properties for the effective delivery of chemotherapeutics, antibiotics, proteins, DNA, RNA, vaccines, genes, etc. Graphene derivatives such as functionalized nano-GO have been effective in delivering anticancer agents without affecting healthy cells. The combining factor for the success of CNMs finding their applicability in drug delivery is due to the excellent opportunity of surface functionalization. For instance, the first in vivo transfection example by using a polyfunctionalized fullerene derivative has been recently reported, thus exhibiting their capability in the delivery of nucleic acids. However, toxicity-related issues are to be addressed before and after the CNMs have delivered their payload to finalize their biological fate in the delivery of therapeutics. Although CNMs have immense potential in their application, they have still to find their practical applicability in biomedicine.

10. Future Perspectives

Since the advent of CNMs about 30 years ago, they have established themselves as promising carrier materials in various biomedical sectors such as biosensing, bioimaging, delivery of therapeutics, etc. Despite several advantages, their toxicity concern toward human cells has rung alarm bells for the researchers to seriously monitor this issue. Along with this, their fabrication takes a long time and is expensive, posing a challenge for large-scale production. Therefore, there is a strict need to find solutions to overcome the challenges of producing non-toxic carbon nanomaterials at a relatively fast pace on a large-scale with low production costs.
Covalent and non-covalent functionalization has paved a way for CNMs to expand their applicability into the biomedical arena, but more has to be done to improve their biocompatibility, i.e., interaction with biological surroundings (cells, or tissues, or organs) and biodegradability or elimination from the body. They are extensively used in aeronautics, space, automobile, textile, sports goods, and so on, yet their applicability on human beings for diagnostics and therapeutic use has not translated from the research laboratory to clinical trials. Their therapeutic use in humans is still waiting to surpass the regulatory hurdle of proving their compatibility, safety, and efficacy. There is a need to develop a systematic nanotechnology-based approach to build an environment for their use in vivo in serious and still largely untreatable ailments such as brain tumors, cerebral stroke, or neurological disorders such as Alzheimer’s or Parkinson’s.
Future fabrications of CNMs should be amalgamated with some novel intuitive guiding moieties so that they could directly approach the target cells, or the researchers could devise such carbon nanomaterials that could be driven from the outside directly to the affected tissue/organ, thus circumventing the side effects of the CNMs on the neighboring healthy tissues. Functionalization techniques (covalent and non-covalent), modifying the shape and size, use of solubilizing agents, removal of metallic impurities, administration route, coating with polymers, and/or blood proteins, etc., could be the possible answer to improve the raw hydrophobic CNM’s solubility and biocompatibility. Their cellular uptake (in vitro) and blood circulation and biodistribution (in vivo) largely rely on surface chemistry. Functionalized carbon nanomaterials with improved solubility, targetability, and biocompatibility could successfully find their way to the clinics for the improved delivery of biomolecules (such as RNA, DNA), small drug molecules, proteins, and peptides. As with any nanomaterials intended for drug delivery, a proper risk assessment evaluation of the toxicity concern of CNM-based delivery of therapeutics is required that should ultimately be extended to clinical trials. An array of safety assessments and in vitro/in vivo cytotoxicity evaluations is the need of the hour to test the effectiveness of the CNMs. Hurdles such as the long-term fate of CNMs should be assessed carefully, and the published data from past studies should be thoroughly screened to bring CNMs further toward clinical translation, to be able to make proper use of the promising applications presented in this review.

Author Contributions

Conceptualization, K.K.B. and A.M.; Writing—original draft preparation, A.M.; Writing—review and editing, J.M.R. and K.K.B.; visualization, S.Y.; supervision, P.B., P.P.S., and N.S. All authors have read and agreed to the published version of the manuscript.


The authors acknowledge the funding support from the Sigrid Jusélius Foundation and the Academy of Finland (#309374).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.


  1. Mudshinge, S.R.; Deore, A.B.; Patil, S.; Bhalgat, C.M. Nanoparticles: Emerging carriers for drug delivery. Saudi Pharm. J. 2011, 19, 129–141. [Google Scholar] [CrossRef] [PubMed][Green Version]
  2. Partha, R.; Conyers, J.L. Biomedical applications of functionalized fullerene-based nanomaterials. Int. J. Nanomed. 2009, 4, 261–275. [Google Scholar] [CrossRef][Green Version]
  3. Perkins, B.L.; Naderi, N. Carbon Nanostructures in Bone Tissue Engineering. Open Orthop. J. 2016, 10, 877–899. [Google Scholar] [CrossRef][Green Version]
  4. Erol, O.; Uyan, I.; Hatip, M.; Yilmaz, C.; Tekinay, A.B.; Guler, M.O. Recent advances in bioactive 1D and 2D carbon nanomaterials for biomedical applications. Nanomed. Nanotechnol. Biol. Med. 2018, 4, 2433–2454. [Google Scholar] [CrossRef] [PubMed][Green Version]
  5. Hasnain, M.S.; Nayak, A.K. Background: Carbon nanotubes for targeted drug delivery. In SpringerBriefs in Applied Sciences and Technology; Springer: Singapore, 2019; pp. 1–9. ISBN 978-981-15-0910-0. [Google Scholar]
  6. Kroto, H.W.; Heath, J.R.; O’Brien, S.C.; Curl, R.F.; Smalley, R.E. C60: Buckminsterfullerene. Nature 1985, 318, 162–163. [Google Scholar] [CrossRef]
  7. Zheng, X.T.; Ananthanarayanan, A.; Luo, K.Q.; Chen, P. Glowing graphene quantum dots and carbon dots: Properties, syntheses, and biological applications. Small 2015, 11, 1620–1636. [Google Scholar] [CrossRef]
  8. Iijima, S. Helical microtubules of graphitic carbon. Nature 1991, 354, 56–58. [Google Scholar] [CrossRef]
  9. Novoselov, K.S.; Geim, A.K.; Morozov, S.V.; Jiang, D.; Zhang, Y.; Dubonos, S.V.; Grigorieva, I.V.; Firsov, A.A. Electric Field Effect in Atomically Thin Carbon Films. Science 2004, 306, 666–669. [Google Scholar] [CrossRef] [PubMed][Green Version]
  10. Ugarte, D. Onion-like graphitic particles. Carbon N. Y. 1995, 33, 989–993. [Google Scholar] [CrossRef]
  11. Generalic, E. “Allotrope.” Croatian-English Chemistry Dictionary & Glossary. Available online: (accessed on 30 December 2020).
  12. Welcome To Cheap Tubes. Available online: (accessed on 30 December 2020).
  13. Konios, D.; Stylianakis, M.M.; Stratakis, E.; Kymakis, E. Dispersion behaviour of graphene oxide and reduced graphene oxide. J. Colloid Interface Sci. 2014, 430, 108–112. [Google Scholar] [CrossRef] [PubMed]
  14. Li, H.; Song, S.I.; Song, G.Y.; Kim, I.I. Non-covalently functionalized carbon nanostructures for synthesizing carbon-based hybrid nanomaterials. J. Nanosci. Nanotechnol. 2014, 4, 1425–1440. [Google Scholar] [CrossRef] [PubMed]
  15. Li, T.F.; Xu, Y.H.; Li, K.; Wang, C.; Liu, X.; Yue, Y.; Chen, Z.; Yuan, S.J.; Wen, Y.; Zhang, Q.; et al. Doxorubicin-polyglycerol-nanodiamond composites stimulate glioblastoma cell immunogenicity through activation of autophagy. Acta Biomater. 2019, 86, 381–384. [Google Scholar] [CrossRef]
  16. Zhang, Q.; Wu, Z.; Li, N.; Pu, Y.; Wang, B.; Zhang, T.; Tao, J. Advanced review of graphene-based nanomaterials in drug delivery systems: Synthesis, modification, toxicity and application. Mater. Sci. Eng. C 2017, 77, 1363–1377. [Google Scholar] [CrossRef] [PubMed]
  17. Allen, T.M. Ligand-targeted therapeutics in anticancer therapy. Nat. Rev. Cancer 2002, 2, 750–763. [Google Scholar] [CrossRef]
  18. Yang, D.; Feng, L.; Dougherty, C.A.; Luker, K.E.; Chen, D.; Cauble, M.A.; Banaszak Holl, M.M.; Luker, G.D.; Ross, B.D.; Liu, Z.; et al. In vivo targeting of metastatic breast cancer via tumor vasculature-specific nano-graphene oxide. Biomaterials 2016, 104, 361–371. [Google Scholar] [CrossRef] [PubMed][Green Version]
  19. Li, R.; Wu, R.; Zhao, L.; Wu, M.; Yang, L.; Zou, H. P-glycoprotein antibody functionalized carbon nanotube overcomes the multidrug resistance of human leukemia cells. ACS Nano 2010, 4, 1399–1408. [Google Scholar] [CrossRef] [PubMed]
  20. Lu, H.; Wang, J.; Wang, T.; Zhong, J.; Bao, Y.; Hao, H. Recent Progress on Nanostructures for Drug Delivery Applications. J. Nanomater. 2016, 2016, 5762431. [Google Scholar] [CrossRef][Green Version]
  21. Kim, S.W.; Kyung Lee, Y.; Yeon Lee, J.; Hee Hong, J.; Khang, D. PEGylated anticancer-carbon nanotubes complex targeting mitochondria of lung cancer cells. Nanotechnology 2017, 28, 465102. [Google Scholar] [CrossRef] [PubMed]
  22. Guo, J.; Wang, Y.; Zhao, M. Target-directed functionalized ferrous phosphate-carbon dots fluorescent nanostructures as peroxidase mimetics for cancer cell detection and ROS-mediated therapy. Sens. Actuators B Chem. 2019, 297, 126739. [Google Scholar] [CrossRef]
  23. Jiang, B.P.; Zhou, B.; Lin, Z.; Liang, H.; Shen, X.C. Recent Advances in Carbon Nanomaterials for Cancer Phototherapy. Chem. A Eur. J. 2019, 25, 3993–4004. [Google Scholar] [CrossRef]
  24. Wang, H.; Bi, J.; Zhu, B.-W.; Tan, M. Multicolorful Carbon Dots for Tumor Theranostics. Curr. Med. Chem. 2017, 25, 2894–2909. [Google Scholar] [CrossRef]
  25. Mohajeri, M.; Behnam, B.; Sahebkar, A. Biomedical applications of carbon nanomaterials: Drug and gene delivery potentials. J. Cell. Physiol. 2018, 234, 298–319. [Google Scholar] [CrossRef][Green Version]
  26. Jović, D.; Jaćević, V.; Kuča, K.; Borišev, I.; Mrdjanovic, J.; Petrovic, D.; Seke, M.; Djordjevic, A. The puzzling potential of carbon nanomaterials: General properties, application, and toxicity. Nanomaterials 2020, 10, 1508. [Google Scholar] [CrossRef]
  27. Goodarzi, S.; Da Ros, T.; Conde, J.; Sefat, F.; Mozafari, M. Fullerene: Biomedical engineers get to revisit an old friend. Mater. Today 2017, 20, 460–480. [Google Scholar] [CrossRef][Green Version]
  28. Rehman, A.; Houshyar, S.; Wang, X. Nanodiamond in composite: Biomedical application. J. Biomed. Mater. Res. Part A 2020, 108, 906–922. [Google Scholar] [CrossRef]
  29. Ahlawat, J.; Masoudi Asil, S.; Guillama Barroso, G.; Nurunnabi, M.; Narayan, M. Application of carbon nano onions in the biomedical field: Recent advances and challenges. Biomater. Sci. 2021. [Google Scholar] [CrossRef]
  30. Kushwaha, S.K.S.; Ghoshal, S.; Rai, A.K.; Singh, S. Carbon nanotubes as a novel drug delivery system for anticancer therapy: A review. Braz. J. Pharm. Sci. 2013, 49, 629–643. [Google Scholar] [CrossRef][Green Version]
  31. Ferrari, M. BioMEMS and biomedical nanotechnology. In BioMEMS and Biomedical Nanotechnology; Springer: Berlin/Heidelberg, Germany, 2007; pp. 2–17. ISBN 0387255664. [Google Scholar]
  32. Tsang, S.C.; Chen, Y.K.; Harris, P.J.F.; Green, M.L.H. A simple chemical method of opening and filling carbon nanotubes. Nature 1994, 372, 159–162. [Google Scholar] [CrossRef]
  33. Ajayan, P.M.; Ebbesen, T.W.; Ichihashi, T.; Iijima, S.; Tanigaki, K.; Hiura, H. Opening carbon nanotubes with oxygen and implications for filling. Nature 1993, 362, 522–525. [Google Scholar] [CrossRef]
  34. Ebbesen, T.W. Wetting, filling and decorating carbon nanotubes. J. Phys. Chem. Solids 1996, 57, 951–955. [Google Scholar] [CrossRef]
  35. Gao, H.; Kong, Y.; Cui, D.; Ozkan, C.S. Spontaneous insertion of DNA oligonucleotides into carbon nanotubes. Nano Lett. 2003, 3, 471–473. [Google Scholar] [CrossRef]
  36. Fu, Q.; Weinberg, G.; Su, D.S. Selective filling of carbon nanotubes with metals by selective washing. Xinxing Tan Cailiao New Carbon Mater. 2008, 23, 17–20. [Google Scholar] [CrossRef][Green Version]
  37. De Jonge, N.; Doytcheva, M.; Allioux, M.; Kaiser, M.; Mentink, S.A.M.; Teo, K.B.K.; Lacerda, R.G.; Milne, W.I. Cap closing of thin carbon nanotubes. Adv. Mater. 2005, 17, 451–455. [Google Scholar] [CrossRef]
  38. Monthioux, M. Filling single-wall carbon nanotubes. Carbon N. Y. 2002, 40, 1809–1823. [Google Scholar] [CrossRef]
  39. Van den Broeck, L.; Piluso, S.; Soultan, A.H.; De Volder, M.; Patterson, J. Cytocompatible carbon nanotube reinforced polyethylene glycol composite hydrogels for tissue engineering. Mater. Sci. Eng. C 2019, 98, 1133–1144. [Google Scholar] [CrossRef]
  40. Zhang, P.; Yi, W.; Hou, J.; Yoo, S.; Jin, W.; Yang, Q. A carbon nanotube-gemcitabine-lentinan three-component composite for chemo-photothermal synergistic therapy of cancer. Int. J. Nanomed. 2018, 13, 3069–3080. [Google Scholar] [CrossRef] [PubMed][Green Version]
  41. Komane, P.P.; Kumar, P.; Marimuthu, T.; du Toit, L.C.; Kondiah, P.P.D.; Choonara, Y.E.; Pillay, V. Dexamethasone-loaded, pegylated, vertically aligned, multiwalled carbon nanotubes for potential ischemic stroke intervention. Molecules 2018, 23, 1406. [Google Scholar] [CrossRef] [PubMed][Green Version]
  42. Suo, N.; Wang, M.; Jin, Y.; Ding, J.; Gao, X.; Sun, X.; Zhang, H.; Cui, M.; Zheng, J.; Li, N.; et al. Magnetic multiwalled carbon nanotubes with controlled release of epirubicin: An intravesical instillation system for bladder cancer. Int. J. Nanomed. 2019, 2019, 1241–1254. [Google Scholar] [CrossRef] [PubMed][Green Version]
  43. Akhtari, J.; Faridnia, R.; Kalani, H.; Bastani, R.; Fakhar, M.; Rezvan, H.; Beydokhti, A.K. Potent in vitro antileishmanial activity of a nanoformulation of cisplatin with carbon nanotubes against Leishmania major. J. Glob. Antimicrob. Resist. 2019, 16, 11–16. [Google Scholar] [CrossRef]
  44. Chegeni, M.; Rozbahani, Z.S.; Ghasemian, M.; Mehri, M. Synthesis and application of the calcium alginate/SWCNT-Gl as a bio-nanocomposite for the curcumin delivery. Int. J. Biol. Macromol. 2020, 156, 504–513. [Google Scholar] [CrossRef]
  45. Maleki, R.; Afrouzi, H.H.; Hosseini, M.; Toghraie, D.; Rostami, S. Molecular dynamics simulation of Doxorubicin loading with N-isopropyl acrylamide carbon nanotube in a drug delivery system. Comput. Methods Programs Biomed. 2020, 184, 1–10. [Google Scholar] [CrossRef] [PubMed]
  46. Kavosi, A.; Hosseini Ghale Noei, S.; Madani, S.; Khalighfard, S.; Khodayari, S.; Khodayari, H.; Mirzaei, M.; Kalhori, M.R.; Yavarian, M.; Alizadeh, A.M.; et al. The toxicity and therapeutic effects of single-and multi-wall carbon nanotubes on mice breast cancer. Sci. Rep. 2018, 8, 8375. [Google Scholar] [CrossRef] [PubMed][Green Version]
  47. Kwak, S.Y.; Lew, T.T.S.; Sweeney, C.J.; Koman, V.B.; Wong, M.H.; Bohmert-Tatarev, K.; Snell, K.D.; Seo, J.S.; Chua, N.H.; Strano, M.S. Chloroplast-selective gene delivery and expression in planta using chitosan-complexed single-walled carbon nanotube carriers. Nat. Nanotechnol. 2019, 14, 447–455. [Google Scholar] [CrossRef]
  48. Ohta, T.; Hashida, Y.; Yamashita, F.; Hashida, M. Development of Novel Drug and Gene Delivery Carriers Composed of Single-Walled Carbon Nanotubes and Designed Peptides With PEGylation. J. Pharm. Sci. 2016, 105, 2815–2824. [Google Scholar] [CrossRef] [PubMed][Green Version]
  49. Kumar, S.; Rani, R.; Dilbaghi, N.; Tankeshwar, K.; Kim, K.H. Carbon nanotubes: A novel material for multifaceted applications in human healthcare. Chem. Soc. Rev. 2017, 158–196. [Google Scholar] [CrossRef] [PubMed]
  50. Herlem, G.; Picaud, F.; Girardet, C.; Micheau, O. Carbon Nanotubes: Synthesis, Characterization, and Applications in Drug-Delivery Systems. In Nanocarriers for Drug Delivery; Elsevier: Amsterdam, The Netherlands, 2019; pp. 469–529. ISBN 9780128140338. [Google Scholar]
  51. Kumar, N.; Kumbhat, S. Essentials in Nanoscience and Nanotechnology. In Essentials in Nanoscience and Nanotechnology; Wiley: Hoboken, NJ, USA, 2016; pp. 29–76. ISBN 9781119096122. [Google Scholar]
  52. Elhissi, A.M.A.; Ahmed, W.; Hassan, I.U.; Dhanak, V.R.; D’Emanuele, A. Carbon Nanotubes in Cancer Therapy and Drug Delivery. J. Drug Deliv. 2012, 2012, 10. [Google Scholar] [CrossRef]
  53. Tasis, D.; Tagmatarchis, N.; Bianco, A.; Prato, M. Chemistry of carbon nanotubes. Chem. Rev. 2006, 106, 1105–1136. [Google Scholar] [CrossRef] [PubMed]
  54. Dai, H. Carbon nanotubes: Synthesis, integration, and properties. Acc. Chem. Res. 2002, 35, 1035–1044. [Google Scholar] [CrossRef]
  55. Dinesh, B.; Bianco, A.; Ménard-Moyon, C. Designing multimodal carbon nanotubes by covalent multi-functionalization. Nanoscale 2016, 8, 18596–18611. [Google Scholar] [CrossRef] [PubMed]
  56. Ravi Kiran, A.V.V.V.; Kusuma Kumari, G.; Krishnamurthy, P.T. Carbon nanotubes in drug delivery: Focus on anticancer therapies. J. Drug Deliv. Sci. Technol. 2020, 59, 1–12. [Google Scholar] [CrossRef]
  57. Vaisman, L.; Wagner, H.D.; Marom, G. The role of surfactants in dispersion of carbon nanotubes. Adv. Colloid Interface Sci. 2006, 128–130, 37–46. [Google Scholar] [CrossRef]
  58. Sinani, V.A.; Gheith, M.K.; Yaroslavov, A.A.; Rakhnyanskaya, A.A.; Sun, K.; Mamedov, A.A.; Wicksted, J.P.; Kotov, N.A. Aqueous dispersions of single-wall and multiwall carbon nanotubes with designed amphiphilic polycations. J. Am. Chem. Soc. 2005, 127, 3463–3472. [Google Scholar] [CrossRef]
  59. Iijima, S. Carbon nanotubes: Past, present, and future. Phys. B Condens. Matter 2002, 323, 1–5. [Google Scholar] [CrossRef]
  60. Hiraoka, T.; Bandow, S.; Shinohara, H.; Iijima, S. Control on the diameter of single-walled carbon nanotubes by changing the pressure in floating catalyst CVD. Carbon N. Y. 2006, 44, 1853–1859. [Google Scholar] [CrossRef]
  61. Xue, Y. Carbon Nanotubes for Biomedical Applications. In Industrial Applications of Carbon Nanotubes; William Andrew: Norwich, NY, USA, 2017; pp. 323–346. ISBN 9780323415316. [Google Scholar]
  62. Hwang, Y.; Park, S.H.; Lee, J.W. Applications of functionalized carbon nanotubes for the therapy and diagnosis of cancer. Polymers 2017, 9, 13. [Google Scholar] [CrossRef] [PubMed][Green Version]
  63. Shanbhag, V.K.L.; Prasad, K.S. Graphene based sensors in the detection of glucose in saliva-a promising emerging modality to diagnose diabetes mellitus. Anal. Methods 2016, 8, 6255–6259. [Google Scholar] [CrossRef]
  64. Kim, P.; Odom, T.W.; Huang, J.L.; Lieber, C.M. Electronic density of states of atomically resolved single-walled carbon nanotubes: Van hove singularities and end states. Phys. Rev. Lett. 1999, 82, 1225–1228. [Google Scholar] [CrossRef][Green Version]
  65. Charlier, J.; Lambin, P. Electronic structure of carbon nanotubes with chiral symmetry. Phys. Rev. B Condens. Matter Mater. Phys. 1998, 57, R15 037–R15 039. [Google Scholar] [CrossRef]
  66. Upadhyayula, V.K.K.; Gadhamshetty, V. Appreciating the role of carbon nanotube composites in preventing biofouling and promoting biofilms on material surfaces in environmental engineering: A review. Biotechnol. Adv. 2010, 28, 802–816. [Google Scholar] [CrossRef] [PubMed]
  67. Schipper, M.L.; Nakayama-Ratchford, N.; Davis, C.R.; Kam, N.W.S.; Chu, P.; Liu, Z.; Sun, X.; Dai, H.; Gambhir, S.S. A pilot toxicology study of single-walled carbon nanotubes in a small sample of mice. Nat. Nanotechnol. 2008, 3, 216–221. [Google Scholar] [CrossRef] [PubMed]
  68. Yang, S.T.; Guo, W.; Lin, Y.; Deng, X.Y.; Wang, H.F.; Sun, H.F.; Liu, Y.F.; Wang, X.; Wang, W.; Chen, M.; et al. Biodistribution of pristine single-walled carbon nanotubes in vivo. J. Phys. Chem. C 2007, 111, 17761–17764. [Google Scholar] [CrossRef]
  69. Saikia, N. Functionalized Carbon Nanomaterials in Drug Delivery: Emergent Perspectives from Application. In Novel Nanomaterials—Synthesis and Applications; IntechOpen: London, UK, 2018; pp. 231–255. ISBN 978-1-83881-460-1. [Google Scholar]
  70. Saikia, N.; Deka, R.C. A comparison of the effect of nanotube chirality and electronic properties on the π-π Interaction of single-wall carbon nanotubes with pyrazinamide antitubercular drug. Int. J. Quantum Chem. 2013, 113, 1272–1284. [Google Scholar] [CrossRef]
  71. Kang, J.H.; Kim, H.S.; Shin, U.S. Thermo conductive carbon nanotube-framed membranes for skin heat signal-responsive transdermal drug delivery. Polym. Chem. 2017, 8, 3154–3163. [Google Scholar] [CrossRef]
  72. Asghar, W.; Shafiee, H.; Velasco, V.; Sah, V.R.; Guo, S.; El Assal, R.; Inci, F.; Rajagopalan, A.; Jahangir, M.; Anchan, R.M.; et al. Toxicology Study of Single-walled Carbon Nanotubes and Reduced Graphene Oxide in Human Sperm. Sci. Rep. 2016, 6, 30270. [Google Scholar] [CrossRef] [PubMed]
  73. Paul, S.J.; Gupta, B.K.; Chandra, P. Probing the electrical and dielectric properties of polyaniline multi-walled carbon nanotubes nanocomposites doped in different protonic acids. Polym. Bull. 2020, 1–17. [Google Scholar] [CrossRef]
  74. Shi, X.; Zheng, Y.; Wang, C.; Yue, L.; Qiao, K.; Wang, G.; Wang, L.; Quan, H. Dual stimulus responsive drug release under the interaction of pH value and pulsatile electric field for a bacterial cellulose/sodium alginate/multi-walled carbon nanotube hybrid hydrogel. RSC Adv. 2015, 5, 41820–41829. [Google Scholar] [CrossRef]
  75. Seyfoori, A.; Sarfarazijami, S.; Seyyed Ebrahimi, S.A. pH-responsive carbon nanotube-based hybrid nanogels as the smart anticancer drug carrier. Artif. Cells Nanomed. Biotechnol. 2019, 47, 1437–1443. [Google Scholar] [CrossRef][Green Version]
  76. Mehrjouei, E.; Akbarzadeh, H.; Shamkhali, A.N.; Abbaspour, M.; Salemi, S.; Abdi, P. Delivery of Cisplatin Anti-Cancer Drug from Carbon, Boron Nitride, and Silicon Carbide Nanotubes Forced by Ag-Nanowire: A Comprehensive Molecular Dynamics Study. Mol. Pharm. 2017, 14, 2273–2284. [Google Scholar] [CrossRef]
  77. Gutiérrez-Hernández, J.M.; Escobar-García, D.M.; Escalante, A.; Flores, H.; González, F.J.; Gatenholm, P.; Toriz, G. In vitro evaluation of osteoblastic cells on bacterial cellulose modified with multi-walled carbon nanotubes as scaffold for bone regeneration. Mater. Sci. Eng. C 2017, 75, 445–453. [Google Scholar] [CrossRef] [PubMed]
  78. Karimi, A.; Erfan, M.; Mortazavi, S.A.; Ghorbani-Bidkorbeh, F.; Kobarfard, F.; Shirazi, F.H. Functionalisation of carbon nanotubes by methotrexate and study of synchronous photothermal effect of carbon nanotube and anticancer drug on cancer cell death. IET Nanobiotechnol. 2019, 13, 52–57. [Google Scholar] [CrossRef]
  79. Sheikh, A.H.; Khalid, A.; Khan, F.; Begum, A. Fluorescent Gadolinium(III)-Oligopeptide Complexes and Carbon Nanotube Composite as Dual Modality Anticancer Agents. ChemistrySelect 2019, 4, 228–235. [Google Scholar] [CrossRef]
  80. Kabanov, A.V. Polymer genomics: An insight into pharmacology and toxicology of nanomedicines. Adv. Drug Deliv. Rev. 2006, 30, 1597–1621. [Google Scholar] [CrossRef] [PubMed][Green Version]
  81. Lanone, S.; Boczkowski, J. Biomedical Applications and Potential Health Risks of Nanomaterials: Molecular Mechanisms. Curr. Mol. Med. 2006, 6, 651–661. [Google Scholar] [CrossRef] [PubMed]
  82. Maeda, H. The enhanced permeability and retention (EPR) effect in tumor vasculature: The key role of tumor-selective macromolecular drug targeting. Adv. Enzym. Regul. 2001, 41, 189–201. [Google Scholar] [CrossRef]
  83. Chu, Y.; Tang, D.; Ke, Z.; Ma, J.; Li, R. Polyethylenimine-functionalized multiwalled carbon nanotube for the adsorption of hydrogen sulfide. J. Appl. Polym. Sci. 2017, 2017, 1–9. [Google Scholar] [CrossRef]
  84. Singh, N.; Sachdev, A.; Gopinath, P. Polysaccharide Functionalized Single Walled Carbon Nanotubes as Nanocarriers for Delivery of Curcumin in Lung Cancer Cells. J. Nanosci. Nanotechnol. 2017, 18, 1534–1541. [Google Scholar] [CrossRef]
  85. Jogi, H.; Maheshwari, R.; Raval, N.; Kuche, K.; Tambe, V.; Mak, K.K.; Pichika, M.R.; Tekade, R.K. Carbon nanotubes in the delivery of anticancer herbal drugs. Nanomedicine 2018, 13, 1187–1220. [Google Scholar] [CrossRef] [PubMed]
  86. Rathod, V.; Tripathi, R.; Joshi, P.; Jha, P.K.; Bahadur, P.; Tiwari, S. Paclitaxel Encapsulation into Dual-Functionalized Multi-Walled Carbon Nanotubes. AAPS PharmSciTech 2019, 20, 1–13. [Google Scholar] [CrossRef]
  87. Hossein Panahi, F.; Peighambardoust, S.J.; Davaran, S.; Salehi, R. Development and characterization of PLA-mPEG copolymer containing iron nanoparticle-coated carbon nanotubes for controlled delivery of Docetaxel. Polymer 2017, 117, 117–131. [Google Scholar] [CrossRef]
  88. Li, Z.; Tozer, T.; Alisaraie, L. Molecular Dynamics Studies for Optimization of Noncovalent Loading of Vinblastine on Single-Walled Carbon Nanotube. J. Phys. Chem. C 2016, 120, 4061–4070. [Google Scholar] [CrossRef]
  89. Wu, W.; Li, R.; Bian, X.; Zhu, Z.; Ding, D.; Li, X.; Jia, Z.; Jiang, X.; Hu, Y. Covalently combining carbon nanotubes with anticancer agent: Preparation and antitumor activity. ACS Nano 2009, 22, 2740–2750. [Google Scholar] [CrossRef]
  90. Dintchevaa, T.; Carrocciod, S.; Arrigoab, R.; Bellaviaa, S.; Cristian Gambarottic, N. Carbon nanotubes-based nanohybrids for multifunctional nanocomposites. J. King Saud Univ. Sci. 2017, 29, 502–509. [Google Scholar] [CrossRef]
  91. Wang, C.; Li, W. Preparation, Characterization, and in Vitro and Vivo Antitumor Activity of Oridonin-Conjugated Multiwalled Carbon Nanotubes Functionalized with Carboxylic Group. J. Nanomater. 2016, 2016, 1–8. [Google Scholar] [CrossRef]
  92. Zhao, Q.; Wang, X.; Yang, M.; Li, X.; Mao, Y.; Guan, X.; Di, D.; Wang, S. Multi-stimuli responsive mesoporous carbon nano-platform gated by human serum albumin for cancer thermo-chemotherapy. Colloids Surfaces B Biointerfaces 2019, 184, 1–11. [Google Scholar] [CrossRef] [PubMed]
  93. Mehra, N.K.; Jain, N.K. One platform comparison of estrone and folic acid anchored surface engineered MWCNTs for doxorubicin delivery. Mol. Pharm. 2015, 12, 630–643. [Google Scholar] [CrossRef]
  94. Douradinha, B.; Doolan, D.L. Harnessing immune responses against Plasmodium for rational vaccine design. Trends Parasitol. 2011, 6, 274–283. [Google Scholar] [CrossRef]
  95. Mogensen, T.H. Pathogen recognition and inflammatory signaling in innate immune defenses. Clin. Microbiol. Rev. 2009, 22, 240–273. [Google Scholar] [CrossRef] [PubMed][Green Version]
  96. Konduru, N.V.; Tyurina, Y.Y.; Feng, W.; Basova, L.V.; Belikova, N.A.; Bayir, H.; Clark, K.; Rubin, M.; Stolz, D.; Vallhov, H.; et al. Phosphatidylserine targets single-walled carbon nanotubes to professional phagocytes in vitro and in vivo. PLoS ONE 2009, 4, e4398. [Google Scholar] [CrossRef]
  97. Pescatori, M.; Bedognetti, D.; Venturelli, E.; Ménard-Moyon, C.; Bernardini, C.; Muresu, E.; Piana, A.; Maida, G.; Manetti, R.; Sgarrella, F.; et al. Functionalized carbon nanotubes as immunomodulator systems. Biomaterials 2013, 34, 4395–4403. [Google Scholar] [CrossRef][Green Version]
  98. Orecchioni, M.; Bedognetti, D.; Sgarrella, F.; Marincola, F.M.; Bianco, A.; Delogu, L.G. Impact of carbon nanotubes and graphene on immune cells. J. Transl. Med. 2014, 12, 1–11. [Google Scholar] [CrossRef] [PubMed][Green Version]
  99. Yang, W.; Thordarson, P.; Gooding, J.J.; Ringer, S.P.; Braet, F. Carbon nanotubes for biological and biomedical applications. Nanotechnology 2007, 18, 1–12. [Google Scholar] [CrossRef]
  100. Atkinson, H.; Chalmers, R. Delivering the goods: Viral and non-viral gene therapy systems and the inherent limits on cargo DNA and internal sequences. Genetica 2010, 138, 485–498. [Google Scholar] [CrossRef]
  101. Md Saquib Hasnain, A.K.N. Carbon Nanotubes in Gene Delivery. In Springer Briefs in Applied Sciences and Technology; Springer: Hoboken, NJ, USA, 2019; pp. 75–87. ISBN 978-981-15-0909-4. [Google Scholar]
  102. Varkouhi, A.K.; Foillard, S.; Lammers, T.; Schiffelers, R.M.; Doris, E.; Hennink, W.E.; Storm, G. SiRNA delivery with functionalized carbon nanotubes. Int. J. Pharm. 2011, 416, 419–425. [Google Scholar] [CrossRef] [PubMed]
  103. Li, J.; Li, M.; Tian, L.; Qiu, Y.; Yu, Q.; Wang, X.; Guo, R.; He, Q. Facile strategy by hyaluronic acid functional carbon dot-doxorubicin nanoparticles for CD44 targeted drug delivery and enhanced breast cancer therapy. Int. J. Pharm. 2020, 578, 119122. [Google Scholar] [CrossRef] [PubMed]
  104. Li, Y.; Niu, Y.; Zhu, J.; Gao, C.; Xu, Q.; He, Z.; Chen, D.; Xu, M.; Liu, Y. Tailor-made legumain/pH dual-responsive doxorubicin prodrug-embedded nanoparticles for efficient anticancer drug delivery and: In situ monitoring of drug release. Nanoscale 2020, 12, 2673–2685. [Google Scholar] [CrossRef]
  105. Shahabi, M.; Raissi, H. Payload delivery of anticancer drug Tegafur with the assistance of graphene oxide nanosheet during biomembrane penetration: Molecular dynamics simulation survey. Appl. Surf. Sci. 2020, 517, 146186. [Google Scholar] [CrossRef]
  106. Yang, J.; Su, H.; Sun, W.; Cai, J.; Liu, S.; Chai, Y.; Zhang, C. Dual chemodrug-loaded single-walled carbon nanohorns for multimodal imaging-guided chemo-photothermal therapy of tumors and lung metastases. Theranostics 2018, 8, 1966–1984. [Google Scholar] [CrossRef]
  107. Oskoueian, A.; Amin Matori, K.; Bayat, S.; Oskoueian, E.; Ostovan, F.; Toozandehjani, M. Fabrication, Characterization, and Functionalization of Single-Walled Carbon Nanotube Conjugated with Tamoxifen and Its Anticancer Potential against Human Breast Cancer Cells. J. Nanomater. 2018, 2018. [Google Scholar] [CrossRef][Green Version]
  108. Sobhani, Z.; Behnam, M.A.; Emami, F.; Dehghanian, A.; Jamhiri, I. Photothermal therapy of melanoma tumor using multiwalled carbon nanotubes. Int. J. Nanomed. 2017, 12, 4509–4517. [Google Scholar] [CrossRef] [PubMed][Green Version]
  109. Fiorica, C.; Mauro, N.; Pitarresi, G.; Scialabba, C.; Palumbo, F.S.; Giammona, G. Double-Network-Structured Graphene Oxide-Containing Nanogels as Photothermal Agents for the Treatment of Colorectal Cancer. Biomacromolecules 2017, 18, 1010–1018. [Google Scholar] [CrossRef]
  110. Ko, N.R.; Nafiujjaman, M.; Lee, J.S.; Lim, H.N.; Lee, Y.K.; Kwon, I.K. Graphene quantum dot-based theranostic agents for active targeting of breast cancer. RSC Adv. 2017, 7, 11420–11427. [Google Scholar] [CrossRef][Green Version]
  111. Fan, Z.; Zhou, S.; Garcia, C.; Fan, L.; Zhou, J. PH-Responsive fluorescent graphene quantum dots for fluorescence-guided cancer surgery and diagnosis. Nanoscale 2017, 9, 4928–4933. [Google Scholar] [CrossRef] [PubMed][Green Version]
  112. Eldridge, B.N.; Bernish, B.W.; Fahrenholtz, C.D.; Singh, R. Photothermal Therapy of Glioblastoma Multiforme Using Multiwalled Carbon Nanotubes Optimized for Diffusion in Extracellular Space. ACS Biomater. Sci. Eng. 2016, 2, 963–976. [Google Scholar] [CrossRef] [PubMed][Green Version]
  113. Raza, K.; Kumar, D.; Kiran, C.; Kumar, M.; Guru, S.K.; Kumar, P.; Arora, S.; Sharma, G.; Bhushan, S.; Katare, O.P. Conjugation of docetaxel with multiwalled carbon nanotubes and codelivery with piperine: Implications on pharmacokinetic profile and anticancer activity. Mol. Pharm. 2016, 13, 2423–2432. [Google Scholar] [CrossRef] [PubMed]
  114. Pal, S.K. Versatile photoluminescence from graphene and its derivatives. Carbon N. Y. 2015, 88, 86–112. [Google Scholar] [CrossRef]
  115. Pattnaik, S.; Swain, K.; Lin, Z. Graphene and graphene-based nanocomposites: Biomedical applications and biosafety. J. Mater. Chem. B 2016, 4, 7813–7831. [Google Scholar] [CrossRef] [PubMed]
  116. Nurunnabi, M.; Khatun, Z.; Nafiujjaman, M.; Lee, D.G.; Lee, Y.K. Surface coating of graphene quantum dots using mussel-inspired polydopamine for biomedical optical imaging. ACS Appl. Mater. Interfaces 2013, 5, 8246–8253. [Google Scholar] [CrossRef]
  117. Zamani, M.; Rostami, M.; Aghajanzadeh, M.; Kheiri Manjili, H.; Rostamizadeh, K.; Danafar, H. Mesoporous titanium [email protected] zinc oxide–graphene oxide nanocarriers for colon-specific drug delivery. J. Mater. Sci. 2018, 53, 1634–1645. [Google Scholar] [CrossRef]
  118. Lu, Y.J.; Lan, Y.H.; Chuang, C.C.; Lu, W.T.; Chan, L.Y.; Hsu, P.W.; Chen, J.P. Injectable thermo-sensitive chitosan hydrogel containing CPT-11-loaded EGFR-targeted graphene oxide and SLP2 shRNA for localized drug/gene delivery in glioblastoma therapy. Int. J. Mol. Sci. 2020, 21, 7111. [Google Scholar] [CrossRef]
  119. Ren, T.; Wang, Y.; Yu, Q.; Li, M. Synthesis of antimicrobial peptide-grafted graphene oxide nanosheets with high antimicrobial efficacy. Mater. Lett. 2019, 235, 42–45. [Google Scholar] [CrossRef]
  120. Khalili, R.; Zarrintaj, P.; Jafari, S.H.; Vahabi, H.; Saeb, M.R. Electroactive poly (p-phenylene sulfide)/r-graphene oxide/chitosan as a novel potential candidate for tissue engineering. Int. J. Biol. Macromol. 2020, 154, 18–24. [Google Scholar] [CrossRef]
  121. Hummers, W.S.; Offeman, R.E. Preparation of Graphitic Oxide. J. Am. Chem. Soc. 1958, 80, 1339. [Google Scholar] [CrossRef]
  122. Cui, X.; Xu, S.; Wang, X.; Chen, C. The nano-bio interaction and biomedical applications of carbon nanomaterials. Carbon N. Y. 2018, 138, 436–450. [Google Scholar] [CrossRef]
  123. Rowley-Neale, S.J.; Randviir, E.P.; Abo Dena, A.S.; Banks, C.E. An overview of recent applications of reduced graphene oxide as a basis of electroanalytical sensing platforms. Appl. Mater. Today 2018, 10, 218–226. [Google Scholar] [CrossRef]
  124. Badami, D.V. X-Ray studies of graphite formed by decomposing silicon carbide. Carbon N. Y. 1965, 3, 53–54. [Google Scholar] [CrossRef]
  125. Yang, K.; Wan, J.; Zhang, S.; Zhang, Y.; Lee, S.T.; Liu, Z. In vivo pharmacokinetics, long-term biodistribution, and toxicology of PEGylated graphene in mice. ACS Nano 2011, 5, 516–522. [Google Scholar] [CrossRef] [PubMed]
  126. Zhang, S.; Yang, K.; Feng, L.; Liu, Z. In vitro and in vivo behaviors of dextran functionalized graphene. Carbon2 2011, 49, 4040–4049. [Google Scholar] [CrossRef]
  127. Layek, R.K.; Uddin, M.E.; Kim, N.H.; Tak Lau, A.K.; Lee, J.H. Noncovalent functionalization of reduced graphene oxide with pluronic F127 and its nanocomposites with gum arabic. Compos. Part B Eng. 2017, 128, 155–163. [Google Scholar] [CrossRef]
  128. Fang, M.; Long, J.; Zhao, W.; Wang, L.; Chen, G. pH-responsive chitosan-mediated graphene dispersions. Langmuir 2010, 26, 16771–16774. [Google Scholar] [CrossRef]
  129. Feng, L.; Zhang, S.; Liu, Z. Graphene based gene transfection. Nanoscale 2011, 3, 1252–1257. [Google Scholar] [CrossRef] [PubMed]
  130. Prabhakar, N.; Näreoja, T.; Von Haartman, E.; Şen Karaman, D.; Burikov, S.A.; Dolenko, T.A.; Deguchi, T.; Mamaeva, V.; Hänninen, P.E.; Vlasov, I.I.; et al. Functionalization of graphene oxide nanostructures improves photoluminescence and facilitates their use as optical probes in preclinical imaging. Nanoscale 2015, 7, 10410–10420. [Google Scholar] [CrossRef]
  131. Sun, X.; Liu, Z.; Welsher, K.; Robinson, J.T.; Goodwin, A.; Zaric, S.; Dai, H. Nano-graphene oxide for cellular imaging and drug delivery. Nano Res. 2008, 1, 203–212. [Google Scholar] [CrossRef] [PubMed][Green Version]
  132. Kwon, Y.; Lee, B.S.; Park, S.; Yu, W.R. A facile route to mechanically robust graphene oxide fibers. RSC Adv. 2019, 9, 20248–20255. [Google Scholar] [CrossRef][Green Version]
  133. Boran, G.; Tavakoli, S.; Dierking, I.; Kamali, A.R.; Ege, D. Synergistic effect of graphene oxide and zoledronic acid for osteoporosis and cancer treatment. Sci. Rep. 2020, 10, 7827. [Google Scholar] [CrossRef] [PubMed]
  134. Islami, M.; Zarrabi, A.; Tada, S.; Kawamoto, M.; Isoshima, T.; Ito, Y. Controlled quercetin release from high-capacity-loading hyperbranched polyglycerol-functionalized graphene oxide. Int. J. Nanomed. 2018, 13, 6059–6071. [Google Scholar] [CrossRef][Green Version]
  135. Yu, X.; Gao, D.; Gao, L.; Lai, J.; Zhang, C.; Zhao, Y.; Zhong, L.; Jia, B.; Wang, F.; Chen, X.; et al. Inhibiting Metastasis and Preventing Tumor Relapse by Triggering Host Immunity with Tumor-Targeted Photodynamic Therapy Using Photosensitizer-Loaded Functional Nanographenes. ACS Nano 2017, 11, 10147–10158. [Google Scholar] [CrossRef] [PubMed]
  136. Cheon, Y.A.; Bae, J.H.; Chung, B.G. Reduced Graphene Oxide Nanosheet for Chemo-photothermal Therapy. Langmuir 2016, 32, 2731–2736. [Google Scholar] [CrossRef] [PubMed]
  137. Fong, Y.T.; Chen, C.H.; Chen, J.P. Intratumoral delivery of doxorubicin on folate-conjugated graphene oxide by in-situ forming thermo-sensitive hydrogel for breast cancer therapy. Nanomaterials 2017, 7, 388. [Google Scholar] [CrossRef] [PubMed][Green Version]
  138. Shao, L.; Zhang, R.; Lu, J.; Zhao, C.; Deng, X.; Wu, Y. Mesoporous silica coated polydopamine functionalized reduced graphene oxide for synergistic targeted chemo-photothermal therapy. ACS Appl. Mater. Interfaces 2017, 9, 1226–1236. [Google Scholar] [CrossRef] [PubMed]
  139. Paul, A.; Hasan, A.; Al Kindi, H.; Gaharwar, A.K.; Rao, V.T.S.; Nikkhah, M.; Shin, S.R.; Krafft, D.; Dokmeci, M.R.; Shum-Tim, D.; et al. Injectable graphene oxide/hydrogel-based angiogenic gene delivery system for vasculogenesis and cardiac repair. ACS Nano 2014, 8, 8050–8062. [Google Scholar] [CrossRef] [PubMed][Green Version]
  140. Wang, X.; Sun, X.; Lao, J.; He, H.; Cheng, T.; Wang, M.; Wang, S.; Huang, F. Multifunctional graphene quantum dots for simultaneous targeted cellular imaging and drug delivery. Colloids Surfaces B Biointerfaces 2014, 122, 638–644. [Google Scholar] [CrossRef]
  141. Abdelhamid, H.N.; Dowaidar, M.; Hällbrink, M.; Langel, Ü. Gene delivery using cell penetrating peptides-zeolitic imidazolate frameworks. Microporous Mesoporous Mater. 2020, 300, 110173. [Google Scholar] [CrossRef]
  142. Tian, B.; Wang, C.; Zhang, S.; Feng, L.; Liu, Z. Photothermally enhanced photodynamic therapy delivered by nano-graphene oxide. ACS Nano 2011, 5, 7000–7009. [Google Scholar] [CrossRef] [PubMed]
  143. Cao, X.; Zheng, S.; Zhang, S.; Wang, Y.; Yang, X.; Duan, H.; Huang, Y.; Chen, Y. Functionalized graphene oxide with hepatocyte targeting as anti-tumor drug and gene intracellular transporters. J. Nanosci. Nanotechnol. 2015, 15, 2052–2059. [Google Scholar] [CrossRef] [PubMed]
  144. Liu, X.; Ma, D.; Tang, H.; Tan, L.; Xie, Q.; Zhang, Y.; Ma, M.; Yao, S. Polyamidoamine dendrimer and oleic acid-functionalized graphene as biocompatible and efficient gene delivery vectors. ACS Appl. Mater. Interfaces 2014, 6, 8173–8183. [Google Scholar] [CrossRef] [PubMed]
  145. Mahdavi, M.; Rahmani, F.; Nouranian, S. Molecular simulation of pH-dependent diffusion, loading, and release of doxorubicin in graphene and graphene oxide drug delivery systems. J. Mater. Chem. B 2016, 4, 7441–7451. [Google Scholar] [CrossRef] [PubMed]
  146. Zhao, X.; Yang, L.; Li, X.; Jia, X.; Liu, L.; Zeng, J.; Guo, J.; Liu, P. Functionalized graphene oxide nanoparticles for cancer cell-specific delivery of antitumor drug. Bioconjug. Chem. 2015, 26, 128–136. [Google Scholar] [CrossRef]
  147. Farazi, R.; Vaezi, M.R.; Molaei, M.J.; Saeidifar, M.; Behnam-Ghader, A.A. Effect of pH and temperature on doxorubicin hydrochloride release from magnetite/graphene oxide nanocomposites. Mater. Today Proc. 2018, 5, 15726–15732. [Google Scholar] [CrossRef]
  148. Afzal, H.; Ikram, M.; Ali, S.; Shahzadi, A.; Aqeel, M.; Haider, A.; Imran, M.; Ali, S. Enhanced drug efficiency of doped ZnO-GO (graphene oxide) nanocomposites, a new gateway in drug delivery systems (DDSs). Mater. Res. Express 2019, 7, 1–9. [Google Scholar] [CrossRef]
  149. Katuwavila, N.P.; Amarasekara, Y.; Jayaweera, V.; Rajaphaksha, C.; Gunasekara, C.; Perera, I.C.; Amaratunga, G.A.J.; Weerasinghe, L. Graphene Oxide–Based Nanocomposite for Sustained Release of Cephalexin. J. Pharm. Sci. 2020, 109, 1130–1135. [Google Scholar] [CrossRef]
  150. Tiwari, H.; Karki, N.; Pal, M.; Basak, S.; Verma, R.K.; Bal, R.; Kandpal, N.D.; Bisht, G.; Sahoo, N.G. Functionalized graphene oxide as a nanocarrier for dual drug delivery applications: The synergistic effect of quercetin and gefitinib against ovarian cancer cells. Colloids Surfaces B Biointerfaces 2019, 178, 452–459. [Google Scholar] [CrossRef]
  151. Pulingam, T.; Thong, K.L.; Appaturi, J.N.; Nordin, N.I.; Dinshaw, I.J.; Lai, C.W.; Leo, B.F. Synergistic antibacterial actions of graphene oxide and antibiotics towards bacteria and the toxicological effects of graphene oxide on human epidermal keratinocytes. Eur. J. Pharm. Sci. 2020, 142, 105087. [Google Scholar] [CrossRef] [PubMed]
  152. Mahdavi, M.; Fattahi, A.; Tajkhorshid, E.; Nouranian, S. Molecular Insights into the Loading and Dynamics of Doxorubicin on PEGylated Graphene Oxide Nanocarriers. ACS Appl. Bio Mater. 2020, 3, 1354–1363. [Google Scholar] [CrossRef]
  153. Kumawat, M.K.; Thakur, M.; Gurung, R.B.; Srivastava, R. Graphene Quantum Dots for Cell Proliferation, Nucleus Imaging, and Photoluminescent Sensing Applications. Sci. Rep. 2017, 7, 15858. [Google Scholar] [CrossRef] [PubMed]
  154. Li, S.; Zhou, S.; Li, Y.; Li, X.; Zhu, J.; Fan, L.; Yang, S. Exceptionally High Payload of the IR780 Iodide on Folic Acid-Functionalized Graphene Quantum Dots for Targeted Photothermal Therapy. ACS Appl. Mater. Interfaces 2017, 9, 22332–22341. [Google Scholar] [CrossRef] [PubMed]
  155. Chen, F.; Gao, W.; Qiu, X.; Zhang, H.; Liu, L.; Liao, P.; Fu, W.; Luo, Y. Graphene quantum dots in biomedical applications: Recent advances and future challenges. Front. Lab. Med. 2017, 1, 192–199. [Google Scholar] [CrossRef]
  156. Pistone, A.; Iannazzo, D.; Ansari, S.; Milone, C.; Salamò, M.; Galvagno, S.; Cirmi, S.; Navarra, M. Tunable doxorubicin release from polymer-gated multiwalled carbon nanotubes. Int. J. Pharm. 2016, 515, 30–36. [Google Scholar] [CrossRef]
  157. Tian, Z.; Yao, X.; Ma, K.; Niu, X.; Grothe, J.; Xu, Q.; Liu, L.; Kaskel, S.; Zhu, Y. Metal-Organic Framework/Graphene Quantum Dot Nanoparticles Used for Synergistic Chemo- and Photothermal Therapy. ACS Omega 2017, 2, 1249–1258. [Google Scholar] [CrossRef][Green Version]
  158. Zheng, F.F.; Zhang, P.H.; Xi, Y.; Chen, J.J.; Li, L.L.; Zhu, J.J. Aptamer/Graphene Quantum Dots Nanocomposite Capped Fluorescent Mesoporous Silica Nanoparticles for Intracellular Drug Delivery and Real-Time Monitoring of Drug Release. Anal. Chem. 2015, 87, 11739–11745. [Google Scholar] [CrossRef]
  159. Ding, H.; Zhang, F.; Zhao, C.; Lv, Y.; Ma, G.; Wei, W.; Tian, Z. Beyond a Carrier: Graphene Quantum Dots as a Probe for Programmatically Monitoring Anti-Cancer Drug Delivery, Release, and Response. ACS Appl. Mater. Interfaces 2017, 9, 27396–27401. [Google Scholar] [CrossRef]
  160. Liu, W.; Speranza, G. Functionalization of Carbon Nanomaterials for Biomedical Applications. C J. Carbon Res. 2019, 5, 72. [Google Scholar] [CrossRef][Green Version]
  161. Nakamura, E.; Isobe, H. Functionalized Fullerenes in Water. The First 10 Years of Their Chemistry, Biology, and Nanoscience. Acc. Chem. Res. 2003, 36, 807–815. [Google Scholar] [CrossRef]
  162. Diederich, F.; Gómez-López, M. Supramolecular fullerene chemistry. Chem. Soc. Rev. 1999, 28, 263–277. [Google Scholar] [CrossRef]
  163. Xie, Q.; Pérez-Cordero, E.; Echegoyen, L. Electrochemical Detection of C606- and C706-: Enhanced Stability of Fullerides in Solution. J. Am. Chem. Soc. 1992, 114, 3978–3980. [Google Scholar] [CrossRef]
  164. Yan, W.; Seifermann, S.M.; Pierrat, P.; Bräse, S. Synthesis of highly functionalized C60 fullerene derivatives and their applications in material and life sciences. Org. Biomol. Chem. 2015, 13, 25–54. [Google Scholar] [CrossRef][Green Version]
  165. Rajagopalan, M.; Oh, I.K. Fullerenol-based electroactive artificial muscles utilizing biocompatible polyetherimide. ACS Nano 2011, 5, 2248–2256. [Google Scholar] [CrossRef] [PubMed]
  166. Zhao, L.; Li, H.; Tan, L. A novel fullerene-based drug delivery system delivering doxorubicin for potential lung cancer therapy. J. Nanosci. Nanotechnol. 2017, 17, 5147–5154. [Google Scholar] [CrossRef]
  167. Hazrati, M.K.; Bagheri, Z.; Bodaghi, A. Application of C30B15N15 heterofullerene in the isoniazid drug delivery: DFT studies. Phys. E Low Dimens. Syst. Nanostruct. 2017, 89, 72–76. [Google Scholar] [CrossRef]
  168. Tan, L.; Wu, T.; Tang, Z.W.; Xiao, J.Y.; Zhuo, R.X.; Shi, B.; Liu, C.J. Water-soluble photoluminescent fullerene capped mesoporous silica for pH-responsive drug delivery and bioimaging. Nanotechnology 2016, 27, 315104. [Google Scholar] [CrossRef]
  169. Ryan, J.J.; Bateman, H.R.; Stover, A.; Gomez, G.; Norton, S.K.; Zhao, W.; Schwartz, L.B.; Lenk, R.; Kepley, C.L. Fullerene Nanomaterials Inhibit the Allergic Response. J. Immunol. 2007, 179, 659–672. [Google Scholar] [CrossRef][Green Version]
  170. Dellinger, A.; Zhou, Z.; Connor, J.; Madhankumar, A.; Pamujula, S.; Sayes, C.M.; Kepley, C.L. Application of fullerenes in nanomedicine: An update. Nanomedicine 2013, 8, 1191–1208. [Google Scholar] [CrossRef] [PubMed][Green Version]
  171. Ashcroft, J.M.; Tsyboulski, D.A.; Hartman, K.B.; Zakharian, T.Y.; Marks, J.W.; Weisman, R.B.; Rosenblum, M.G.; Wilson, L.J. Fullerene (C60) immunoconjugates: Interaction of water-soluble C60 derivatives with the murine anti-gp240 melanoma antibody. Chem. Commun. 2006, 2006, 3004–3006. [Google Scholar] [CrossRef]
  172. Kim, J.; Lee, H.; Lee, J.Y.; Park, K.H.; Kim, W.; Lee, J.H.; Kang, H.J.; Hong, S.W.; Park, H.J.; Lee, S.; et al. Photosensitized Production of Singlet Oxygen via C60 Fullerene Covalently Attached to Functionalized Silica-coated Stainless-Steel Mesh: Remote Bacterial and Viral Inactivation. Appl. Catal. B Environ. 2020, 270, 118862. [Google Scholar] [CrossRef]
  173. Mochalin, V.N.; Shenderova, O.; Ho, D.; Gogotsi, Y. The properties and applications of nanodiamonds. Nat. Nanotechnol. 2012, 7, 11–23. [Google Scholar] [CrossRef]
  174. Angus, J.C. Diamond synthesis by chemical vapor deposition: The early years. Diam. Relat. Mater. 2014, 49, 77–86. [Google Scholar] [CrossRef]
  175. Liu, Y.Y.; Chang, B.M.; Chang, H.C. Nanodiamond-enabled biomedical imaging. Nanomedicine 2020, 15, 1599–1616. [Google Scholar] [CrossRef]
  176. Nunn, N.; Prabhakar, N.; Reineck, P.; Magidson, V.; Kamiya, E.; Heinz, W.F.; Torelli, M.D.; Rosenholm, J.; Zaitsev, A.; Shenderova, O. Brilliant blue, green, yellow, and red fluorescent diamond particles: Synthesis, characterization, and multiplex imaging demonstrations. Nanoscale 2019, 11, 11584–11595. [Google Scholar] [CrossRef]
  177. Prabhakar, N.; Rosenholm, J.M. Nanodiamonds for advanced optical bioimaging and beyond. Curr. Opin. Colloid Interface Sci. 2019, 39, 220–231. [Google Scholar] [CrossRef]
  178. Reineck, P.; Trindade, L.F.; Havlik, J.; Stursa, J.; Heffernan, A.; Elbourne, A.; Orth, A.; Capelli, M.; Cigler, P.; Simpson, D.A.; et al. Not All Fluorescent Nanodiamonds Are Created Equal: A Comparative Study. Part. Part. Syst. Charact. 2019, 36, 1900009. [Google Scholar] [CrossRef]
  179. Kaur, R.; Badea, I. Nanodiamonds as novel nanomaterials for biomedical applications: Drug delivery and imaging systems. Int. J. Nanomed. 2013, 8, 203–220. [Google Scholar] [CrossRef]
  180. Wilson, E.R.; Parker, L.M.; Orth, A.; Nunn, N.; Torelli, M.; Shenderova, O.; Gibson, B.C.; Reineck, P. The effect of particle size on nanodiamond fluorescence and colloidal properties in biological media. Nanotechnology 2019, 30, 385704. [Google Scholar] [CrossRef] [PubMed]
  181. Mengesha, A.E.; Youan, B.B.C. Nanodiamonds for drug delivery systems. In Diamond-Based Materials for Biomedical Applications; Elsevier: Amsterdam, The Netherlands, 2013; pp. 186–205. ISBN 9780857093400. [Google Scholar]
  182. Rehor, I.; Slegerova, J.; Kucka, J.; Proks, V.; Petrakova, V.; Adam, M.-P.; Treussart, F.; Turner, S.; Bals, S.; Sacha, P.; et al. Fluorescent Nanodiamonds Embedded in Biocompatible Translucent Shells. Small 2014, 10, 1106–1115. [Google Scholar] [CrossRef] [PubMed][Green Version]
  183. Von Haartman, E.; Jiang, H.; Khomich, A.A.; Zhang, J.; Burikov, S.A.; Dolenko, T.A.; Ruokolainen, J.; Gu, H.; Shenderova, O.A.; Vlasov, I.I.; et al. Core-shell designs of photoluminescent nanodiamonds with porous silica coatings for bioimaging and drug delivery I: Fabrication. J. Mater. Chem. B 2013, 1, 2358–2366. [Google Scholar] [CrossRef]
  184. Rosenholm, J.M.; Vlasov, I.I.; Burikov, S.A.; Dolenko, T.A.; Shenderova, O.A. Nanodiamond-based composite structures for biomedical imaging and drug delivery. J. Nanosci. Nanotechnol. 2015, 15, 959–971. [Google Scholar] [CrossRef]
  185. Roy, U.; Drozd, V.; Durygin, A.; Rodriguez, J.; Barber, P.; Atluri, V.; Liu, X.; Voss, T.G.; Saxena, S.; Nair, M. Characterization of Nanodiamond-based anti-HIV drug Delivery to the Brain. Sci. Rep. 2018, 8, 1603. [Google Scholar] [CrossRef] [PubMed][Green Version]
  186. Taylor, A.C.; González, C.H.; Miller, B.S.; Edgington, R.J.; Ferretti, P.; Jackman, R.B. Surface functionalisation of nanodiamonds for human neural stem cell adhesion and proliferation. Sci. Rep. 2017, 7, 7307. [Google Scholar] [CrossRef] [PubMed]
  187. Edgington, R.; Jackman, R.B. Neuron growth on nanodiamond. In Nanodiamond; Royal Society of Chemistry: London, UK, 2014; pp. 195–220. ISBN 9781849736398. [Google Scholar]
  188. Bartolome, J.P.; Fragoso, A. Preparation and characterization of carbon nano-onions by nanodiamond annealing and functionalization by radio-frequency Ar/O2 plasma. Fuller. Nanotub. Carbon Nanostruct. 2017, 25, 327–334. [Google Scholar] [CrossRef]
  189. Palkar, A.; Melin, F.; Cardona, C.M.; Elliott, B.; Naskar, A.K.; Edie, D.D.; Kumbhar, A.; Echegoyen, L. Reactivity differences between Carbon Nano Onions (CNOs) prepared by different methods. Chem. Asian J. 2007, 2, 625–633. [Google Scholar] [CrossRef]
  190. Ugarte, D. Curling and closure of graphitic networks under electron-beam irradiation. Nature 1992, 359, 707–709. [Google Scholar] [CrossRef]
  191. Sano, N.; Wang, H.; Alexandrou, I.; Chhowalla, M.; Teo, K.B.K.; Amaratunga, G.A.J.; Iimura, K. Properties of carbon onions produced by an arc discharge in water. J. Appl. Phys. 2002, 92, 2783–2788. [Google Scholar] [CrossRef][Green Version]
  192. Kuznetsov, V.L.; Chuvilin, A.L.; Butenko, Y.V.; Mal’kov, I.Y.; Titov, V.M. Onion-like carbon from ultra-disperse diamond. Chem. Phys. Lett. 1994, 222, 343–348. [Google Scholar] [CrossRef]
  193. Mykhailiv, O.; Lapinski, A.; Molina-Ontoria, A.; Regulska, E.; Echegoyen, L.; Dubis, A.T.; Plonska-Brzezinska, M.E. Influence of the Synthetic Conditions on the Structural and Electrochemical Properties of Carbon Nano-Onions. ChemPhysChem 2015, 16, 2182–2191. [Google Scholar] [CrossRef]
  194. Bystrzejewski, M.; Rummeli, M.H.; Gemming, T.; Lange, H.; Huczko, A. Catalyst-free synthesis of onion-like carbon nanoparticles. Xinxing Tan Cailiao/New Carbon Mater. 2010, 25, 1–8. [Google Scholar] [CrossRef]
  195. Camisasca, A.; Giordani, S. Carbon nano-onions in biomedical applications: Promising theranostic agents. Inorg. Chim. Acta 2017, 468, 67–76. [Google Scholar] [CrossRef]
  196. Bartelmess, J.; Giordani, S. Carbon nano-onions (multi-layer fullerenes): Chemistry and applications. Beilstein J. Nanotechnol. 2014, 5, 1980–1998. [Google Scholar] [CrossRef] [PubMed]
  197. Mamidi, N.; González-Ortiz, A.; Romo, I.L.; Barrera, E.V. Development of functionalized carbon nano-onions reinforced zein protein hydrogel interfaces for controlled drug release. Pharmaceutics 2019, 11, 621. [Google Scholar] [CrossRef][Green Version]
  198. D’Amora, M.; Camisasca, A.; Boarino, A.; Giordani, S.; Arpicco, S. Supramolecular functionalization of carbon nano-onions with hyaluronic acid-phospholipid conjugates for selective targeting of cancer cells. Colloids Surfaces B Biointerfaces 2020, 188, 110779. [Google Scholar] [CrossRef] [PubMed]
  199. Bobrowska, D.M.; Czyrko, J.; Brzezinski, K.; Echegoyen, L.; Plonska-Brzezinska, M.E. Carbon nano-onion composites: Physicochemical characteristics and biological activity. Fuller. Nanotub. Carbon Nanostruct. 2017, 25, 185–192. [Google Scholar] [CrossRef]
  200. Babar, D.G.; Pakhira, B.; Sarkar, S. DNA–carbon nano onion aggregate: Triangle, hexagon, six-petal flower to dead-end network. Appl. Nanosci. 2017, 7, 291–297. [Google Scholar] [CrossRef][Green Version]
  201. Tripathi, K.M.; Bhati, A.; Singh, A.; Gupta, N.R.; Verma, S.; Sarkar, S.; Sonkar, S.K. From the traditional way of pyrolysis to tunable photoluminescent water soluble carbon nano-onions for cell imaging and selective sensing of glucose. RSC Adv. 2016, 6, 37319–37329. [Google Scholar] [CrossRef]
  202. Pakhira, B.; Ghosh, M.; Allam, A.; Sarkar, S. Carbon nano onions cross the blood brain barrier†. RSC Adv. 2016, 6, 29779–29782. [Google Scholar] [CrossRef]
  203. Mamidi, N.; Zuníga, A.E.; Villela-Castrejón, J. Engineering and evaluation of forcespun functionalized carbon nano-onions reinforced poly (ε-caprolactone) composite nanofibers for pH-responsive drug release. Mater. Sci. Eng. C 2020, 112, 110928. [Google Scholar] [CrossRef] [PubMed]
  204. Mamidi, N.; Villela Castrejón, J.; González-Ortiz, A. Rational design and engineering of carbon nano-onions reinforced natural protein nanocomposite hydrogels for biomedical applications. J. Mech. Behav. Biomed. Mater. 2020, 104, 103696. [Google Scholar] [CrossRef]
  205. Tovar, C.D.G.; Castro, J.I.; Valencia, C.H.; Porras, D.P.N.; Hernandez, J.H.M.; Valencia, M.E.; Velásquez, J.D.; Chaur, M.N. Preparation of chitosan/poly(Vinyl alcohol) nanocomposite films incorporated with oxidized carbon nano-onions (multi-layer fullerenes) for tissue-engineering applications. Biomolecules 2019, 9, 684. [Google Scholar] [CrossRef] [PubMed][Green Version]
  206. Lettieri, S.; Camisasca, A.; D’Amora, M.; Diaspro, A.; Uchida, T.; Nakajima, Y.; Yanagisawa, K.; Maekawa, T.; Giordani, S. Far-red fluorescent carbon nano-onions as a biocompatible platform for cellular imaging. RSC Adv. 2017, 7, 45676–45681. [Google Scholar] [CrossRef][Green Version]
  207. Sok, V.; Fragoso, A. Preparation and characterization of alkaline phosphatase, horseradish peroxidase, and glucose oxidase conjugates with carboxylated carbon nano-onions. Prep. Biochem. Biotechnol. 2018, 48, 136–143. [Google Scholar] [CrossRef]
  208. Kostarelos, K.; Bianco, A.; Prato, M. Promises, facts and challenges for carbon nanotubes in imaging and therapeutics. Nat. Nanotechnol. 2009, 4, 627–633. [Google Scholar] [CrossRef] [PubMed]
  209. Jastrzębska, A.M.; Kurtycz, P.; Olszyna, A.R. Recent advances in graphene family materials toxicity investigations. J. Nanoparticle Res. 2012, 14, 1320. [Google Scholar] [CrossRef][Green Version]
  210. Yuan, X.; Zhang, X.; Sun, L.; Wei, Y.; Wei, X. Cellular Toxicity and Immunological Effects of Carbon-based Nanomaterials. Part. Fibre Toxicol. 2019, 16, 18. [Google Scholar] [CrossRef] [PubMed]
  211. Allegri, M.; Perivoliotis, D.K.; Bianchi, M.G.; Chiu, M.; Pagliaro, A.; Koklioti, M.A.; Trompeta, A.F.A.; Bergamaschi, E.; Bussolati, O.; Charitidis, C.A. Toxicity determinants of multi-walled carbon nanotubes: The relationship between functionalization and agglomeration. Toxicol. Rep. 2016, 3, 230–243. [Google Scholar] [CrossRef][Green Version]
  212. Kobayashi, N.; Izumi, H.; Morimoto, Y. Review of toxicity studies of carbon nanotubes. J. Occup. Health 2017, 59, 394–407. [Google Scholar] [CrossRef][Green Version]
  213. Seabra, A.B.; Paula, A.J.; de Lima, R.; Alves, O.L.; Durán, N. Nanotoxicity of graphene and graphene Oxide. Chem. Res. Toxicol. 2014, 27, 159–168. [Google Scholar] [CrossRef] [PubMed]
  214. Alshehri, R.; Ilyas, A.M.; Hasan, A.; Arnaout, A.; Ahmed, F.; Memic, A. Carbon nanotubes in biomedical applications: Factors, mechanisms, and remedies of toxicity. J. Med. Chem. 2016, 59, 8149–8167. [Google Scholar] [CrossRef] [PubMed]
  215. Hobson, D.W.; Guy, R.C. Nanotoxicology. Encycl. Toxicol. Third Ed. 2014, 61, 727–738. [Google Scholar] [CrossRef]
  216. Wang, J.; Cao, S.; Ding, Y.; Ma, F.; Lu, W.; Sun, M. Theoretical investigations of optical origins of fluorescent graphene quantum dots. Sci. Rep. 2016, 6, 24850. [Google Scholar] [CrossRef]
  217. Nam, C.W.; Kang, S.J.; Kang, Y.K.; Kwak, M.K. Cell growth inhibition and apoptosis by SDS-solubilized single-walled carbon nanotubes in normal rat kidney epithelial cells. Arch. Pharmacal Res. 2011, 34, 661–669. [Google Scholar] [CrossRef] [PubMed]
  218. Kim, S.W.; Kim, T.; Kim, Y.S.; Choi, H.S.; Lim, H.J.; Yang, S.J.; Park, C.R. Surface modifications for the effective dispersion of carbon nanotubes in solvents and polymers. Carbon N. Y. 2012, 50, 3–33. [Google Scholar] [CrossRef]
  219. Praena, D.G.; Pichardo, S.; Sánchez, E.; Grilo, A.; Cameán, A.M.; Jos, A. Influence of carboxylic acid functionalization on the cytotoxic effects induced by single wall carbon nanotubes on human endothelial cells (HUVEC). Toxicol. In Vitro 2011, 25, 1883–1888. [Google Scholar] [CrossRef] [PubMed]
  220. Koyama, S.; Kim, Y.A.; Hayashi, T.; Takeuchi, K.; Fujii, C.; Kuroiwa, N.; Koyama, H.; Tsukahara, T.; Endo, M. In vivo immunological toxicity in mice of carbon nanotubes with impurities. Carbon N. Y. 2009, 47, 1365–1372. [Google Scholar] [CrossRef][Green Version]
  221. Aldieri, E.; Fenoglio, I.; Cesano, F.; Gazzano, E.; Gulino, G.; Scarano, D.; Attanasio, A.; Mazzucco, G.; Ghigo, D.; Fubini, B. The role of iron impurities in the toxic effects exerted by short multiwalled carbon nanotubes (MWCNT) in murine alveolar macrophages. J. Toxicol. Environ. Heal. Part A Curr. Issues 2013, 76, 1056–1071. [Google Scholar] [CrossRef] [PubMed]
  222. Chong, Y.; Ge, C.; Yang, Z.; Garate, J.A.; Gu, Z.; Weber, J.K.; Liu, J.; Zhou, R. Reduced cytotoxicity of graphene nanosheets mediated by blood-protein coating. ACS Nano 2015, 9, 5713–5724. [Google Scholar] [CrossRef]
  223. Tian, X.; Xiao, B.B.; Wu, A.; Yu, L.; Zhou, J.; Wang, Y.; Wang, N.; Guan, H.; Shang, Z.F. Hydroxylated-graphene quantum dots induce cells senescence in both p53-dependent and -independent manner. Toxicol. Res. 2016, 5, 1639–1648. [Google Scholar] [CrossRef][Green Version]
  224. Nurunnabi, M.; Khatun, Z.; Huh, K.M.; Park, S.Y.; Lee, D.Y.; Cho, K.J.; Lee, Y.K. In Vivo biodistribution and toxicology of carboxylated graphene quantum dots. ACS Nano 2013, 7, 6858–6867. [Google Scholar] [CrossRef] [PubMed]
  225. Garriga, R.; Herrero-Continente, T.; Palos, M.; Cebolla, V.L.; Osada, J.; Muñoz, E.; Rodríguez-Yoldi, M.J. Toxicity of carbon nanomaterials and their potential application as drug delivery systems: In vitro studies in caco-2 and mcf-7 cell lines. Nanomaterials 2020, 10, 1617. [Google Scholar] [CrossRef]
  226. Dasari Shareena, T.P.; McShan, D.; Dasmahapatra, A.K.; Tchounwou, P.B. A Review on Graphene-Based Nanomaterials in Biomedical Applications and Risks in Environment and Health. Nano Micro Lett. 2018, 10, 53. [Google Scholar] [CrossRef]
  227. Chauhan, S.; Jain, N.; Nagaich, U. Nanodiamonds with powerful ability for drug delivery and biomedical applications: Recent updates on in vivo study and patents. J. Pharm. Anal. 2020, 10, 1–12. [Google Scholar] [CrossRef] [PubMed]
  228. Zhang, Q.; Mochalin, V.N.; Neitzel, I.; Knoke, I.Y.; Han, J.; Klug, C.A.; Zhou, J.G.; Lelkes, P.I.; Gogotsi, Y. Fluorescent PLLA–nanodiamond composites for bone tissue engineering. Biomaterials 2011, 32, 87–94. [Google Scholar] [CrossRef]
  229. Schrand, A.M. Safety of Nanoparticles: From Manufacturing to Medical Applications; Springer: Berlin/Heidelberg, Germany, 2009; ISBN 978-0-387-78608-7. [Google Scholar]
  230. Yuan, Y.; Wang, X.; Jia, G.; Liu, J.H.; Wang, T.; Gu, Y.; Yang, S.T.; Zhen, S.; Wang, H.; Liu, Y. Pulmonary toxicity and translocation of nanodiamonds in mice. Diam. Relat. Mater. 2010, 19, 291–299. [Google Scholar] [CrossRef]
  231. Mohan, N.; Chen, C.S.; Hsieh, H.H.; Wu, Y.C.; Chang, H.C. In vivo imaging and toxicity assessments of fluorescent nanodiamonds in Caenorhabditis elegans. Nano Lett. 2010, 10, 3692–3699. [Google Scholar] [CrossRef]
  232. Chow, E.K.; Zhang, X.Q.; Chen, M.; Lam, R.; Robinson, E.; Huang, H.; Schaffer, D.; Osawa, E.; Goga, A.; Ho, D. Nanodiamond therapeutic delivery agents mediate enhanced chemoresistant tumor treatment. Sci. Transl. Med. 2011, 3, 73ra21. [Google Scholar] [CrossRef]
  233. Lacerda, L.; Bianco, A.; Prato, M.; Kostarelos, K. Carbon nanotubes as nanomedicines: From toxicology to pharmacology. Adv. Drug Deliv. Rev. 2006, 58, 1460–1470. [Google Scholar] [CrossRef]
  234. Donaldson, K.; Aitken, R.; Tran, L.; Stone, V.; Duffin, R.; Forrest, G.; Alexander, A. Carbon nanotubes: A review of their properties in relation to pulmonary toxicology and workplace safety. Toxicol. Sci. 2006, 92, 5–22. [Google Scholar] [CrossRef][Green Version]
  235. Ali-Boucetta, H.; Nunes, A.; Sainz, R.; Herrero, M.A.; Tian, B.; Prato, M.; Bianco, A.; Kostarelos, K. Asbestos-like pathogenicity of long carbon nanotubes alleviated by chemical functionalization. Angew. Chem. Int. Ed. 2013. [Google Scholar] [CrossRef]
  236. Rungrotmongkol, T.; Arsawang, U.; Iamsamai, C.; Vongachariya, A.; Dubas, S.T.; Ruktanonchai, U.; Soottitantawat, A.; Hannongbua, S. Increased dispersion and solubility of carbon nanotubes noncovalently modified by the polysaccharide biopolymer, chitosan: MD simulations. Chem. Phys. Lett. 2011, 507, 134–137. [Google Scholar] [CrossRef]
  237. Kam, N.W.S.; Liu, Z.; Dai, H. Functionalization of carbon nanotubes via cleavable disulfide bonds for efficient intracellular delivery of siRNA and potent gene silencing. J. Am. Chem. Soc. 2005, 127, 12492–12493. [Google Scholar] [CrossRef]
  238. Russier, J.; León, V.; Orecchioni, M.; Hirata, E.; Virdis, P.; Fozza, C.; Sgarrella, F.; Cuniberti, G.; Prato, M.; Vázquez, E.; et al. Few-Layer Graphene Kills Selectively Tumor Cells from Myelomonocytic Leukemia Patients. Angew. Chem. Int. Ed. 2017, 56, 3014–3019. [Google Scholar] [CrossRef] [PubMed]
  239. Lammers, T.; Ferrari, M. The success of nanomedicine. Nano Today 2020, 31, 100853. [Google Scholar] [CrossRef]
Figure 1. Carbon nanomaterials and their applications in the vast biomedical arena.
Figure 1. Carbon nanomaterials and their applications in the vast biomedical arena.
Carbon 07 00019 g001
Figure 2. Various allotropes of carbon [11].
Figure 2. Various allotropes of carbon [11].
Carbon 07 00019 g002
Figure 3. Single-walled and multiple-walled carbon nanotubes (CNT) [12].
Figure 3. Single-walled and multiple-walled carbon nanotubes (CNT) [12].
Carbon 07 00019 g003
Figure 4. Preparation method of end-capped single single-walled carbon nanotubes (SWCNTs) [30].
Figure 4. Preparation method of end-capped single single-walled carbon nanotubes (SWCNTs) [30].
Carbon 07 00019 g004
Figure 5. Fabrication methods of carbon nanotubes. Adapted from [49].
Figure 5. Fabrication methods of carbon nanotubes. Adapted from [49].
Carbon 07 00019 g005
Figure 6. Various applications of graphene oxide in the biomedical arena. Adapted from [123].
Figure 6. Various applications of graphene oxide in the biomedical arena. Adapted from [123].
Carbon 07 00019 g006
Figure 7. Applications and advantages of nanodiamonds. Adapted from [28].
Figure 7. Applications and advantages of nanodiamonds. Adapted from [28].
Carbon 07 00019 g007
Figure 8. High-resolution TEM image of (A): Carbon onion; (B): Structure of carbon onion. Reproduced with permission from reference [195].
Figure 8. High-resolution TEM image of (A): Carbon onion; (B): Structure of carbon onion. Reproduced with permission from reference [195].
Carbon 07 00019 g008
Figure 9. Graphic illustration of carbon nano-onions (CNOs) functionalization and applications. Adapted from [29].
Figure 9. Graphic illustration of carbon nano-onions (CNOs) functionalization and applications. Adapted from [29].
Carbon 07 00019 g009
Figure 10. SEM photomicrographs of DNA composites (a): DNA-water-soluble carbon nano-onion (wsCNO) at 1 h; (b): Growth at 4 h; (c): Aggregation at 4 h; (d): Triangle formation at 16 h; (e): Hexagon formation; (f): Flower formation; (g): Assorted flower formation; (h): Selected six-petal flower [200].
Figure 10. SEM photomicrographs of DNA composites (a): DNA-water-soluble carbon nano-onion (wsCNO) at 1 h; (b): Growth at 4 h; (c): Aggregation at 4 h; (d): Triangle formation at 16 h; (e): Hexagon formation; (f): Flower formation; (g): Assorted flower formation; (h): Selected six-petal flower [200].
Carbon 07 00019 g010
Figure 11. An insight on the factors causing toxicity, their risk assessment, and deleterious effects on humans as well as the environment by the carbon-based nanomaterials (CNMs).
Figure 11. An insight on the factors causing toxicity, their risk assessment, and deleterious effects on humans as well as the environment by the carbon-based nanomaterials (CNMs).
Carbon 07 00019 g011
Table 1. A brief overview of carbon nano-onions (CNMs) with their advantages and limitations [25,26,27,28,29].
Table 1. A brief overview of carbon nano-onions (CNMs) with their advantages and limitations [25,26,27,28,29].
S. No.Carbon-Based NanomaterialsAdvantagesLimitations in Biomedical Applications
1.Carbon nanotubesHas good mechanical strength, aspect ratio, conductivity, and chemical stability. Offers tunable physical properties (e.g., diameter, length, single-walled vs. multi-walled, surface functionalization, and chirality), biocompatibility, and high surface area.Lack of solubility in aqueous media, non-homogenous in size (diameter and length), and possibilities of metallic impurities. Pristine CNTs being a lightweight powder may enter into the respiratory tract.
2.Graphene/graphene oxide/graphene quantum dotsOffers excellent electrical, optical, and thermal properties. The two-dimensional atomic sheet structure of graphene enables more diverse electronic characteristics than CNTs.Colloidal instability, lack of reproducibility, limited synthetic control, poor chemical stability in the biological environment, susceptibility to the oxidative environment.
3.FullerenesPeculiar photoelectrochemical properties, the possibility of surface modification, and superconductivity.Low aqueous solubility, accumulation in cell membranes, susceptible to degradation in the presence of light and oxygen, susceptible to deactivation process such as quenching.
4.NanodiamondsFluorescence and photoluminescence, biocompatible, smaller size compared to other CNMs, hard, corrosion-resistant, chemical inertness, high electrical resistance, and optical transparency.Difficult to manufacture via covalent manner, tedious to remove toxic organic solvents while fabrication, abrupt drug release, and tendency to aggregate.
5.Carbon nano-onionsUnique electronic and structural properties, including the ability to accept electrons reversibly, a high surface-area to volume ratio, and broad absorption bands.Hydrophobic, low biocompatibility, aggregation, prone to oxidation, low surface chemical reactivity.
Table 2. Recent advancement in carbon nanotube-based delivery.
Table 2. Recent advancement in carbon nanotube-based delivery.
S. No.IndicationDrug/Vaccines/GenesCNT FunctionalizationResultsReferences
1.Cell proliferationTissue engineeringHydrogels of PEG-CNTsPristine CNTs and PEG-CNT hydrogels enhanced the cytocompatibility, viability, and proliferation of L29 fibroblasts.[39]
2.CancerGemcitabine–LentinanMWCNTs/Gemcitabine (Ge)/Lentinan-LeMWCNTs-Ge-Le showed augmented chemo and near IR-photothermal synergistic antitumor activity.[40]
3.Ischemic brain tissueDexamethasonePEGylated vertically aligned MWCNTsLow cytotoxicity was observed on the PC-12 cell line by the MWCNTs.[41]
4.Bladder cancerEpirubicin (Epi)Magnetic MWCNTs-EpiExternally magnetic guided MWCNTs showed enhanced sustained release, prolonged retention behavior, and better antitumor activity than the free epirubicin both in vitro and in vivo.[42]
5.AntileishmanialCisplatin (Ci)Ci-SWCNTs, Ci-MWCNTsCi-MWCNTs showed potent in vitro antileishmanial activity at low concentrations on Leishmania. major.[43]
6.Antibacterial activityCurcuminGlucose-modified calcium alginate single-walled carbon nanotubes (CA/SWCNT-Gl)CA/SWCNT-Gl nanocomposite showed better antibacterial activity against Bacillus cereus and Escherichia coli.[44]
7.Cancer therapyDoxorubicin (DOX)N-isopropyl acrylamide carbon nanotubes loaded with DOXSmaller polymer chain length resulted in more hydrogen bonding with the drug, five mer N-isopropyl acrylamide augmented DOX loading.[45]
8.Cancer therapyDoxorubicinA pH-sensitive conjugate of DOX-loaded SWCNTs and MWCNTsBonds between DOX and MWCNTs were stronger, which resulted in controlled drug release in cancer tissues in comparison to SWCNTs.[46]
9.Genetic engineeringPlastid genomeChitosan complexed SWCNTs utilizing the lipid exchange envelope penetration mechanismChitosan–SWCNTs selectively delivered plasmid DNA to the chloroplast in Eruca sativa, Nasturtum officinale, Nicotiana tabacum, and Soiacia oleracea, and isolated Arabidopsos thaliana mesophyll protoplasts.[47]
10.Peptide deliveryGS-proteinThe casing of SWNTs with polycationic and amphiphilic peptides [H-(-Lys-Trp-Lys-Gly-)7-OH]Seven times more uptake in comparison with the SWCNT–peptide composite without PEGylation.[48]
Table 3. Various carbon nanovectors used in the treatment of tumors.
Table 3. Various carbon nanovectors used in the treatment of tumors.
S. No.Carbon-Based NanovectorsIn VitroIndicationReference
1.Hyaluronic acid-modified carbon dots4T1 cellsIn vivo anti-tumor activity[103]
2.Poly(ethylene glycol)-block-poly(β-benzyl-L-aspartate) (PEG-b-PBLA) polymers, octadecyl amine-p(Asp-API)10 (OAPI) polymers, and legumain-cleavable linker containing doxorubicin (DOX)-carbon quantum dots conjugations (CDs-C9-AANL-DOX)Tumor cellsIn vivo anti-tumor activity[104]
3.Tegafur loaded graphene oxide nanosheetMolecular dynamics simulation survey for drug release across the cell membraneAntitumor activity[105]
4.Epirubicin loaded multi-walled CNTST24 and 5637 cellsBladder cancer[42]
5.Single-walled CNTs4T1 cellsChemo-photothermal therapy[106]
6.Single-walled CNTsHuman breast cancer cell (MCF-7)-[107]
7.Single-walled CNTsA549 and NIH 3T3 cells-[84]
8.Multi-walled CNTsHeLa cellsPhotothermal therapy[108]
9.Double network structured GOHCT116 cellsChemo-photothermal[109]
10.Graphene QDsBT-474, MCF-7 cells-[110]
11.Graphene QDsPANC-1, A-549, HepG2-[111]
12.PEG functionalized multi-walled CNTSU87, U373MG, NHABrain tumor therapy[112]
13.Multi-walled CNTsMCF-7 and MDA-MB-231 human breast cancer cells/rats-[113]
Table 4. Application of graphene derivatives for drug delivery.
Table 4. Application of graphene derivatives for drug delivery.
S. No.Graphene DerivativeTherapeutic AgentsApplication and OutcomesReferences
1.GOZoledronic acidBone marrow-derived mesenchymal stem cells (BM-MSC), and Michigan Cancer Foundation-7 (MCF-7) breast cancer cells[133]
2.Pristine graphene and graphene oxideDoxorubicinIn vitro: pH simulation[145]
3.Graphene oxideDoxorubicinIn vitro: drug release[146]
4.GO-FA-AuNPsDoxorubicinSignificant in vivo tumor reversion in solid tumor model in Balb/c mice[147]
5.GO nanosheets doped into ZnO NPsDoxorubicinGO-doped ZnO NPs displayed higher drug loading efficiency of 89% in comparison to 82% of ZnO. The developed system enhanced the dissolution of the drug.[148]
6.PEG-functionalized GOCephalexinIn vitro, CEF release exhibited burst release followed by sustained release over the 96-h period with a cumulative release of 80%. MIC values stated dose and time-dependent antibacterial activity for GO-PEG-CEF against both Gram positive and Gram negative bacteria.[149]
7.GO-PVPQuercetin and gefitinibDual drug loaded GO-PVP nano-vehicles showed higher drug loading, and cancer cell cytotoxicity was more in contrast to an individual GO-PVP system in PA-1 ovarian cancer cells and compared to their effects on IOSE-364 ovarian epithelial cells.[150]
chloramphenicol and tetracycline
GO potential as an antibacterial along with antibiotic drugs displayed synergistic effects against S. aureus, E. coli, E. faecalis, and P. aeruginosa and the toxicological effects of GO toward human epidermal keratinocytes (HaCaT).[151]
9.PEGylated GODoxorubicinPEGylation of the GO efficiently augmented the average water density around the nanocarrier, which acts as a barricade, leading to the DOX migration to the solvated PEG-free part of the GO surface. The computational results exhibited the fact that increasing the PEG chain length aids DOX loading on the nanocarrier.[152]
Table 5. Recent progress of CNOs in biomedical applications.
Table 5. Recent progress of CNOs in biomedical applications.
S. No.Delivery SystemApplicationResultsReference
1.Polycaprolactone/f-CNO nanocomposite fiberAnticancer drug deliveryDOX release from PCL/f-CNO nanocomposite fiber was pH-dependent. F-CNOs augmented the mechanical strength, hydrophobicity, and biocompatibility of the PCL nanofibers.[203]
2.f-CNO-reinforced zein hydrogelsAnticancer drug deliveryf-CNOs improved the mechanical strength of zein hydrogels. The delivery system exhibited good cytocompatibility against the osteoblast cell line. A pH-responsive sustained drug release over 15 days was observed.[197]
3.f-CNO/gelatin composite hydrogelsAnticancer drug delivery5-FU/f-CNO/Gelatin hydrogels exhibited augmented tensile strength in comparison to pristine gelatin hydrogels. A sustained release of 5-FU for over 15 days was observed, which indicated possible prospects in cartilage tissue engineering and drug delivery.[204]
4.Ox-CNO-loaded chitosan polyvinyl alcohol (CS/PVA/oc-CNO) nanocomposite filmTissue engineering applicationOx-CNO enhanced the stability of the CS/PVA/ox-CNO scaffold. The nanocomposite film displayed no allergic response or pus formation in Wistar rats after subdermal implantation of the scaffold. The CS/PVA/oc-CNO scaffold exhibited tissue regeneration capability.[205]
5.Pristine CNOs (p-CNOs), ox-CNOs, far-red fluorescent-CNOsCellular imaging applicationOx-CNOS and Fluo-CNOs exhibited excellent cytocompatibility against MCF-7 and HeLa cells. Far-red fluorescent images indicated the internalization of fluo-CNOs by the MCF-7 cells, conforming that fluo-CNOs can be utilized as a high-resolution cellular imaging agent as an alternative for organic dyes.[206]
6.DNA sensor composed of glassy carbon electrode (GCE)/pristine-CNOSensing biomolecular interactionThe GCE/CNO nanocomposite DNA sensor sensed the human papillomavirus oncogene DNA sequence via amperometric detection. Modification via electrochemical grafting of the GCE/CNO surface with two different diazonium salts (4-aminophenylacetic acid) PAA and (4-aminophenylmaleimide) PM yielded GCE/CNO/PAA and GCE/CNO/PM nanocomposite. Both surfaces supported the attachment of thiolated or biotinylated short recognition DNA sequences (DNA probes). The large surface area and the enhanced electron transfer properties of this analytical sensor helped in the sensing of biomolecular interactions.[188]
7.CNO-based catalytic biosensorNanobiocatalyst for biosensing applicationCNO-based catalytic biosensor (CNO/enzyme) conjugate retained optimum pH and temperature, displayed stability over a longer duration at 37 °C. The CNO catalytic biosensor efficiently detected the immobilization of various enzymes such as alkaline phosphatase, horseradish peroxidase (HRP), and glucose oxidase (≈0.5 mg of enzyme per mg of CNOs).[207]
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Mahor, A.; Singh, P.P.; Bharadwaj, P.; Sharma, N.; Yadav, S.; Rosenholm, J.M.; Bansal, K.K. Carbon-Based Nanomaterials for Delivery of Biologicals and Therapeutics: A Cutting-Edge Technology. C 2021, 7, 19.

AMA Style

Mahor A, Singh PP, Bharadwaj P, Sharma N, Yadav S, Rosenholm JM, Bansal KK. Carbon-Based Nanomaterials for Delivery of Biologicals and Therapeutics: A Cutting-Edge Technology. C. 2021; 7(1):19.

Chicago/Turabian Style

Mahor, Alok, Prem Prakash Singh, Peeyush Bharadwaj, Neeraj Sharma, Surabhi Yadav, Jessica M. Rosenholm, and Kuldeep K. Bansal. 2021. "Carbon-Based Nanomaterials for Delivery of Biologicals and Therapeutics: A Cutting-Edge Technology" C 7, no. 1: 19.

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop