Biosensors

The metabolic process of the human body produces a large number of gaseous biomarkers. The tracking and monitoring of certain diseases can be achieved through the detection of these markers. Due to the superior specific surface area, large functional groups, good optical transparency, conductivity and interlayer spacing, graphene, and its derivatives are widely used in gas sensing. Herein, the development of graphene and its derivatives in gas-phase biomarker detection was reviewed in terms of the detection principle and the latest detection methods and applications in several common gases, etc. Finally, we summarized the commonly used materials, preparation methods, response mechanisms for NO, NH₃, H₂S, and volatile organic gas VOCs, and other gas detection, and proposed the challenges and prospective applications in this field. Full article

The complete blood count (CBC) is one of the most important clinical steps in clinical diagnosis. The instruments used for CBC are usually expensive and bulky and require well-trained operators. Therefore, it is difficult for medical institutions below the tertiary level to provide these instruments, especially in underprivileged countries. Several reported on-chip blood cell tests are still in their infancy and do not deviate from conventional microscopic or impedance measurement methods. In this study, we (i) combined magnetically activated cell sorting and the differential density method to develop a method to selectively isolate three types of leukocytes from blood and obtain samples with high purity and concentration for portable leukocyte classification using the lens-free shadow imaging technique (LSIT), and (ii) established several shadow parameters to identify the type of leukocytes in a complete leukocyte shadow image by shadow image analysis. The purity of the separated leukocytes was confirmed by flow cytometry. Several shadow parameters such as the “order ratio” and “minimum ratio” were developed to classify the three types of leukocytes. A shadow image library corresponding to each type of leukocyte was created from the tested samples. Compared with clinical reference data, a correlation index of 0.98 was obtained with an average error of 6% and a confidence level of 95%. This technique offers great potential for biological, pharmaceutical, environmental, and clinical applications, especially where point-of-care detection of rare cells is required. Full article

As an emerging and powerful material, aggregation-induced emission luminogens (AIEgens), which could simultaneously provide a precise diagnosis and efficient therapeutics, have exhibited significant superiorities in the field of phototheranostics. Of particular interest is phototheranostics based on AIEgens with the emission in the range of second near-infrared (NIR-II) range (1000–1700 nm), which has promoted the feasibility of their clinical applications by virtue of numerous preponderances benefiting from the extremely long wavelength. In this minireview, we summarize the latest advances in the field of phototheranostics based on NIR-II AIEgens during the past 3 years, including the strategies of constructing NIR-II AIEgens and their applications in different theranostic modalities (FLI-guided PTT, PAI-guided PTT, and multimodal imaging-guided PDT–PTT synergistic therapy); in addition, a brief conclusion of perspectives and challenges in the field of phototheranostics is given at the end. Full article

A magnetic-based immunoassay (MBI) combined with biotin-streptavidin amplification was proposed for butyl benzyl phthalate (BBP) investigation and risk assessment. The values of LOD (limit of detection, IC₁₀) and IC₅₀ were 0.57 ng/mL and 119.61 ng/mL, with a detection range of 0.57–24,977.71 ng/mL for MBI. The specificity, accuracy and precision are well demonstrated. A total of 36 environmental water samples of urban sewage from Zhenjiang, China, were collected and assessed for BBP contamination. The results show that BBP-positive levels ranged from 2.47 to 89.21 ng/mL, with a positive rate of 77.8%. The health effects of BBP in the urban sewage were within a controllable range, and the ambient severity for health (ASI) was below 1.49. The highest value of AS for ecology (ASII) was 7.43, which indicates a potential harm to ecology. The entropy value of risk quotient was below 100, the highest being 59.47, which poses a low risk to the environment and ecology, indicating that there is a need to strengthen BBP controls. The non-carcinogenic risk of BBP exposure from drinking water was higher for females than that for males, and the non-carcinogenic risk from drinking-water and bathing pathways was negligible. This study could provide an alternative method for detecting BBP and essential information for controlling BBP contamination. Full article

Rapid, selective, and cost-effective detection and determination of clinically relevant biomolecule analytes for a better understanding of biological and physiological functions are becoming increasingly prominent. In this regard, biosensors represent a powerful tool to meet these requirements. Recent decades have seen biosensors gaining popularity due to their ability to design sensor platforms that are selective to determine target analytes. Naturally generated receptor units have a high affinity for their targets, which provides the selectivity of a device. However, such receptors are subject to instability under harsh environmental conditions and have consequently low durability. By applying principles of supramolecular chemistry, molecularly imprinted polymers (MIPs) can successfully replace natural receptors to circumvent these shortcomings. This review summarizes the recent achievements and analytical applications of electrosynthesized MIPs, in particular, for the detection of protein-based biomarkers. The scope of this review also includes the background behind electrochemical readouts and the origin of the gate effect in MIP-based biosensors. Full article

Utilizing an appropriate enzyme immobilization strategy is crucial for designing enzyme-based biosensors. Plant virus-like particles represent ideal nanoscaffolds for an extremely dense and precise immobilization of enzymes, due to their regular shape, high surface-to-volume ratio and high density of surface binding sites. In the present work, tobacco mosaic virus (TMV) particles were applied for the co-immobilization of penicillinase and urease onto the gate surface of a field-effect electrolyte-insulator-semiconductor capacitor (EISCAP) with a p-Si-SiO₂-Ta₂O₅ layer structure for the sequential detection of penicillin and urea. The TMV-assisted bi-enzyme EISCAP biosensor exhibited a high urea and penicillin sensitivity of 54 and 85 mV/dec, respectively, in the concentration range of 0.1–3 mM. For comparison, the characteristics of single-enzyme EISCAP biosensors modified with TMV particles immobilized with either penicillinase or urease were also investigated. The surface morphology of the TMV-modified Ta₂O₅-gate was analyzed by scanning electron microscopy. Additionally, the bi-enzyme EISCAP was applied to mimic an XOR (Exclusive OR) enzyme logic gate. Full article

The increasing use of nanomaterials and scalable, high-yield nanofabrication process are revolutionizing the development of novel biosensors. Over the past decades, researches on nanotechnology-mediated biosensing have been on the forefront due to their potential application in healthcare, pharmaceutical, cell diagnosis, drug delivery, and water and air quality monitoring. The advancement of nanoscale science relies on a better understanding of theory, manufacturing and fabrication practices, and the application specific methods. The topology and tunable properties of nanoparticles, a part of nanoscale science, can be changed by different manufacturing processes, which separate them from their bulk counterparts. In the recent past, different nanostructures, such as nanosphere, nanorods, nanofiber, core–shell nanoparticles, nanotubes, and thin films, have been exploited to enhance the detectability of labelled or label-free biological molecules with a high accuracy. Furthermore, these engineered-materials-associated transducing devices, e.g., optical waveguides and metasurface-based scattering media, widened the horizon of biosensors over a broad wavelength range from deep-ultraviolet to far-infrared. This review provides a comprehensive overview of the major scientific achievements in nano-biosensors based on optical fiber, nanomaterials and terahertz-domain metasurface-based refractometric, labelled and label-free nano-biosensors. Full article

Although iron is an essential constituent for almost all living organisms, iron dyshomeostasis at a cellular level may trigger oxidative stress and neuronal damage. Hence, there are numerous reported carbon dots (CDs) that have been synthesized and applied to determine intracellular iron ions. However, among reported CDs focused to detect Fe³⁺ ions, only a few CDs have been designed to specifically determine Fe²⁺ ions over Fe³⁺ ions for monitoring of intracellular Fe²⁺ ions. We have developed the nitrogen-doped CDs (NCDs) for fluorescence turn-off detection of Fe²⁺ at cellular level. The as-synthesized NCDs exhibit a strong blue fluorescence and low cytotoxicity, acting as fluorescence probes to detect Fe²⁺ as low as 0.702 µM in aqueous solution within 2 min and visualize intracellular Fe²⁺ in the concentration range from 0 to 500 µM within 20 min. The as-prepared NCDs possess some advantages such as high biocompatibility, strong fluorescence properties, selectivity, and rapidity for intracellular Fe²⁺ monitoring, making NCDs an excellent nanoprobe for biosensing of intracellular ferrous ions. Full article

Measuring pH has become a major key for determining health conditions, and food safety. The traditional pH assessment approaches are costly and offer low sensitivity. Here, a novel pH sensor based on a pH-responsive hydrogel has been developed. A Fresnel lens pattern was replicated on the surface of the pH-responsive hydrogel using the replica mould method. The pH sensors were tested in a pH range of 4–7. Introducing various pH solutions to the pH sensor led to volumetric shifts as the hydrogel swelled with pH. Consequently, the dimensions of the replicated Fresnel lens changed, modifying the focal length and the focus efficiency of the optical sensor. As a result, the measured optical power at a fixed distance from the sensor changed with pH. The optical sensor showed the best performance in the acidic region when pH changed from 4.5 to 5.5, in which the recorded power increased by 13%. The sensor exhibited high sensitivity to pH changes with a short respond time in a reversible manner. The developed pH optical sensor may have applications in medical point-of-care diagnostics and wearable continuous pH detection devices. Full article

In this paper, we propose an improved electrochemical platform based on graphene for the detection of DNA hybridization. Commercial screen-printed carbon electrodes (SPCEs) were used for this purpose due to their ease of functionalization and miniaturization opportunities. SPCEs were modified with reduced graphene oxide (RGO), offering a suitable surface for further functionalization. Therefore, aryl-carboxyl groups were integrated onto RGO-modified electrodes by electrochemical reduction of the corresponding diazonium salt to provide enough reaction sites for the covalent immobilization of amino-modified DNA probes. Our final goal was to determine the optimum conditions needed to fabricate a simple, label-free RGO-based electrochemical platform to detect the hybridization between two complementary single-stranded DNA molecules. Each modification step in the fabrication process was monitored by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) using [Fe(CN)₆]^3−/4− as a redox reporter. Although, the diazonium electrografted layer displayed the expected blocking effect of the charge transfer, the next steps in the modification procedure resulted in enhanced electron transfer properties of the electrode interface. We suggest that the improvement in the charge transfer after the DNA hybridization process could be exploited as a prospective sensing feature. The morphological and structural characterization of the modified electrodes performed by scanning electron microscopy (SEM) and Raman spectroscopy, respectively, were used to validate different modification steps in the platform fabrication process. Full article

Cancer is the top cause of death globally. Developing smart nanomedicines that are capable of diagnosis and therapy (theranostics) in one–nanoparticle systems are highly desirable for improving cancer treatment outcomes. The magnetic nanoplatforms are the ideal system for cancer theranostics, because of their diverse physiochemical properties and biological effects. In particular, a biocompatible iron oxide nanoparticle based magnetic nanoplatform can exhibit multiple magnetic–responsive behaviors under an external magnetic field and realize the integration of diagnosis (magnetic resonance imaging, ultrasonic imaging, photoacoustic imaging, etc.) and therapy (magnetic hyperthermia, photothermal therapy, controlled drug delivery and release, etc.) in vivo. Furthermore, due to considerable variation among tumors and individual patients, it is a requirement to design iron oxide nanoplatforms by the coordination of diverse functionalities for efficient and individualized theranostics. In this article, we will present an up–to–date overview on iron oxide nanoplatforms, including both iron oxide nanomaterials and those that can respond to an externally applied magnetic field, with an emphasis on their applications in cancer theranostics. Full article

One of the advantages of surface plasmon resonance is its sensitivity and real-time analyses performed by this method. These characteristics allow us to further investigate the interactions of challenging proteins like Rap1-interacting factor 1 (Rif1). Rif1 is a crucial protein responsible for regulating different cellular processes including DNA replication, repair, and transcription. Mammalian Rif1 is yet to be fully characterized, partly because it is predicted to be intrinsically disordered for a large portion of its polypeptide. This protein has recently been the target of research as a potential biomarker in many cancers. Therefore, finding its most potent interacting partner is of utmost importance. Previous studies showed Rif1’s affinity towards structured DNAs and amongst them, T₆G₂₄ was superior. Recent studies have shown mouse Rif1 (muRif1) C-terminal domain’s (CTD) role in binding to G-quadruplexes (G4). There were many concerns in investigating the Rif1 and G4 interaction, which can be minimized using SPR. Therefore, for the first time, we have assessed its binding with G4 at nano-molar concentrations with SPR which seems to be crucial for its binding analyses. Our results indicate that muRif1-CTD has a high affinity for this G4 sequence as it shows a very low K_D (6 ± 1 nM). Full article

Detection of microbial contamination in water is imperative to ensure water quality. We have developed an electrochemical method for the detection of E. coli using bi-functional magnetic nanoparticle (MNP) conjugates. The bi-functional MNP conjugates were prepared by terminal-specific conjugation of anti-E. coli IgG antibody and the electroactive marker ferrocene. The bi-functional MNP conjugate possesses both E. coli-specific binding and electroactive properties, which were studied in detail. The conjugation efficiency of ferrocene and IgG antibodies with amine-functionalized MNPs was investigated. Square-wave voltammetry enabled the detection of E. coli concentrations ranging from 10¹–10⁷ cells/mL in a dose-dependent manner, as ferrocene-specific current signals were inversely dependent on E. coli concentrations, completely suppressed at concentrations higher than 10⁷ cells/mL. The developed electrochemical method is highly sensitive (10 cells/mL) and, coupled to magnetic separation, provides specific signals within 1h. Overall, the bi-functional conjugates serve as ideal candidates for electrochemical detection of waterborne bacteria. This approach can be applied for the detection of other bacteria and viruses. Full article

As one of the pivotal signal molecules, hydrogen peroxide (H₂O₂) has been demonstrated to play important roles in many physiological processes of plants. Continuous monitoring of H₂O₂ in vivo could help understand its regulation mechanism more clearly. In this study, a disposable electrochemical microsensor for H₂O₂ was developed. This microsensor consists of three parts: low-cost stainless-steel wire with a diameter of 0.1 mm modified by gold nanoparticles (disposable working electrode), an untreated platinum wire with a diameter of 0.1 mm (counter electrode), and an Ag/AgCl wire with a diameter of 0.1 mm (reference electrode), respectively. The microsensor could detect H₂O₂ in levels from 10 to 1000 µM and exhibited excellent selectivity. On this basis, the dynamic change in H₂O₂ in the vein of tomato leaf under high salinity was continuously monitored in vivo. The results showed that the production of H₂O₂ could be induced by high salinity within two hours. This study suggests that the disposable electrochemical microsensor not only suits continuously detecting H₂O₂ in microscopic plant tissue in vivo but also reduces the damage to plants. Overall, our strategy will help to pave the foundation for further investigation of the generation, transportation, and elimination mechanism of H₂O₂ in plants. Full article

Biological water contamination detection-based assays are essential to test water quality; however, these assays are prone to false-positive results and inaccuracies, are time-consuming, and use complicated procedures to test large water samples. Herein, we show a simple detection and counting method for E. coli in the water samples involving a combination of DNAzyme sensor, microfluidics, and computer vision strategies. We first isolated E. coli into individual droplets containing a DNAzyme mixture using droplet microfluidics. Upon bacterial cell lysis by heating, the DNAzyme mixture reacted with a particular substrate present in the crude intracellular material (CIM) of E. coli. This event triggers the dissociation of the fluorophore-quencher pair present in the DNAzyme mixture leading to a fluorescence signal, indicating the presence of E. coli in the droplets. We developed an algorithm using computer vision to analyze the fluorescent droplets containing E. coli in the presence of non-fluorescent droplets. The algorithm can detect and count fluorescent droplets representing the number of E. coli present in the sample. Finally, we show that the developed method is highly specific to detect and count E. coli in the presence of other bacteria present in the water sample. Full article

A stress group should be subdivided into eustress (low-stress) and distress (high-stress) groups to better evaluate personal cognitive abilities and mental/physical health. However, it is challenging because of the inconsistent pattern in brain activation. We aimed to ascertain the necessity of subdividing the stress groups. The stress group was screened by salivary alpha-amylase (sAA) and then, the brain’s hemodynamic reactions were measured by functional near-infrared spectroscopy (fNIRS) based on the near-infrared biosensor. We compared the two stress subgroups categorized by sAA using a newly designed emotional stimulus-response paradigm with an international affective picture system (IAPS) to enhance hemodynamic signals induced by the target effect. We calculated the laterality index for stress (LIS) from the measured signals to identify the dominantly activated cortex in both the subgroups. Both the stress groups exhibited brain activity in the right frontal cortex. Specifically, the eustress group exhibited the largest brain activity, whereas the distress group exhibited recessive brain activity, regardless of positive or negative stimuli. LIS values were larger in the order of the eustress, control, and distress groups; this indicates that the stress group can be divided into eustress and distress groups. We built a foundation for subdividing stress groups into eustress and distress groups using fNIRS. Full article

Surface-enhanced Raman spectroscopy (SERS) is a promising tool that can be used in the detection of molecular changes triggered by disease development. Cardiovascular diseases (CVDs) are caused by multiple pathologies originating at the cellular level. The identification of these deteriorations can provide a better understanding of CVD mechanisms, and the monitoring of the identified molecular changes can be employed in the development of novel biosensor tools for early diagnostics. We applied plasmonic SERS nanosensors to assess changes in the properties of erythrocytes under normotensive and hypertensive conditions in the animal model. We found that spontaneous hypertension in rats leads (i) to a decrease in the erythrocyte plasma membrane fluidity and (ii) to a decrease in the mobility of the heme of the membrane-bound hemoglobin. We identified SERS parameters that can be used to detect pathological changes in the plasma membrane and submembrane region of erythrocytes. Full article

C-reactive protein (CRP) is a non-specific biomarker of inflammation and may be associated with cardiovascular disease. In recent studies, systemic inflammatory responses have also been observed in cases of coronavirus disease 2019 (COVID-19). Molecularly imprinted polymers (MIPs) have been developed to replace natural antibodies with polymeric materials that have low cost and high stability and could thus be suitable for use in a home-care system. In this work, a MIP-based electrochemical sensing system for measuring CRP was developed. Such a system can be integrated with microfluidics and electronics for lab-on-a-chip technology. MIP composition was optimized using various imprinting template (CRP peptide) concentrations. Tungsten disulfide (WS₂) was doped into the MIPs. Doping not only enhances the electrochemical response accompanying the recognition of the template molecules but also raises the top of the sensing range from 1.0 pg/mL to 1.0 ng/mL of the imprinted peptide. The calibration curve of the WS₂-doped peptide-imprinted polymer-coated electrodes in the extended-gate field-effect transistor platform was obtained and used for the measurement of CRP concentration in real human serum. Full article

Bacteriophages, abbreviated as “phages”, have been developed as emerging nanoprobes for the detection of a wide variety of biological species, such as biomarker molecules and pathogens. Nanosized phages can display a certain length of exogenous peptides of arbitrary sequence or single-chain variable fragments (scFv) of antibodies that specifically bind to the targets of interest, such as animal cells, bacteria, viruses, and protein molecules. Metal nanoparticles generally have unique plasmon resonance effects. Metal nanoparticles such as gold, silver, and magnetism are widely used in the field of visual detection. A phage can be assembled with metal nanoparticles to form an organic–inorganic hybrid probe due to its nanometer-scale size and excellent modifiability. Due to the unique plasmon resonance effect of this composite probe, this technology can be used to visually detect objects of interest under a dark-field microscope. In summary, this review summarizes the recent advances in the development of phage-based probes for ultra-sensitive detection of various bio-species, outlining the advantages and limitations of detection technology of phage-based assays, and highlighting the commonly used editing technologies of phage genomes such as homologous recombination and clustered regularly interspaced palindromic repeats/CRISPR-associated proteins system (CRISPR-Cas). Finally, we discuss the possible scenarios for clinical application of phage-probe-based detection methods. Full article