Metallic Nanomaterials with Biomedical Applications

Abstract

Metallic nanomaterials have attracted extensive attention in various fields due to their photocatalytic, photosensitive, thermal conducting, electrical conducting and semiconducting properties. Among all these fields, metallic nanomaterials are of particular importance in biomedical sensing for the detection of different analytes, such as proteins, toxins, metal ions, nucleotides, anions and saccharides. However, many problems remain to be solved, such as the synthesis method and modification of target metallic nanoparticles, inadequate sensitivity and stability in biomedical sensing and the biological toxicity brought by metallic nanomaterials. Thus, this Special Issue aims to collect research or review articles focused on electrochemical biosensing, such as metallic nanomaterial-based electrochemical sensors and biosensors, metallic oxide-modified electrodes, biological sensing based on metallic nanomaterials, metallic nanomaterial-based biological sensing devices and chemometrics for metallic nanomaterial-based biological sensing. Meanwhile, studies related to the synthesis and characterization of metallic nanomaterials are also welcome, and both experimental and theoretical studies are welcome for contribution as well.

1. Introduction

In recent years, with the continuous development of nanotechnology, nanomaterials have found use in various fields. Among all these fields, nanomaterials are particularly garnering attention in biomedicine [1]. They can be applied to magnetic resonance imaging (MRI) technology [2,3], targeted technology [4], drug delivery [5], therapeutics for radiotherapy and chemotherapy [6], and biomedical sensors for the efficient detection of various indicators of the body [7,8,9]. When macroscopic objects are subdivided into nanosized particles, their optical, thermal, electrical, mechanical and chemical properties will be significantly different from those of bulk solids [10]. The properties of nanomaterials were found to be size-dependent [11]. Specifically, when the size of nanomaterials is less than or equal to the wavelength of the light wave, the de Broglie wavelength or coherent length of the superconducting state, the physical and chemical properties of nanomaterials, such as resistance, reflectance to light, and melting point, will change with changes in size [12,13,14]. In addition, nanomaterials will acquire many special properties that bulk solid materials do not have [15]. Because of the properties of the nanomaterials mentioned above, their applications in the biomedical field are being rapidly explored.

Among all the applications of nanomaterials in biomedical science, biomedical sensing plays an important role. In all categories of nanomaterials, metallic nanomaterials are usually used to enhance the performance of biosensors in biomedicine [16,17]. Metallic nanomaterials commonly used in the field of biomedical sensing include but are not limited to TiO₂, Fe₃O₄, MnO₂, ZnO, Co₃O₄, Au, Ag, Pt and Pd [18,19,20,21,22]. The common synthesis methods of metallic nanomaterials include hydrothermal, sol–gel, atomic layer deposition and vapor deposition methods, etc. For example, Purniawan et al. used a low surface roughness and highly homogenous TiO₂ layer synthesized through atomic layer deposition (ALD) to enhance the refractive index of the waveguide core and improve the sensitivity of the sensor, and the sensing mechanism was investigated by SEM and other characterization methods [23]. However, in Purniawan’s research, TiO₂ did not have the highest refractive index compared to the other nanomaterials, but to meet the bending ability, TiO₂ was selected at last. Therefore, to obtain more desirable properties of metallic nanomaterials, material modification during synthesis was investigated. Compared to using one type of metallic nanomaterial alone, the modification of metallic nanomaterials is highly focused on making them more stable on the sensing surface area during chemical processing and making the materials safe to the ecosystem. Modification methods, including the synthesis of different nanomaterials with different dimensions, were investigated to obtain special properties. Chen et al. introduced several general synthetic strategies applied to 2D metallic nanomaterials and summarized their applications [24]. Song et al. indicated that 2D metallic nanomaterials can improve sensing ability, consequently reducing the detection limits of a wide range of target analytes, including biomolecules and heavy metals HMs [25]. In addition, doping can also be used to modify the properties of metallic nanoparticles. Meng et al. synthesized gold nanoparticles combined with ferric oxide nanoparticles and carbon nanotubes to detect the tumor biomarker alpha fetoprotein (AFP) with a limit of detection (LOD) of 0.04 ng mL⁻¹, and it also demonstrated a good selectivity for AFP detection against other interferential substances [26]. Based on the studies discussed above, it is found that the metallic nanomaterials modified on the sensing area are very important to the detection performance, as they can determine the functions, such as sensitivity, stability, selectivity, LOD, etc., of sensors [27]. Thus, how to choose the modification materials of the sensor is an interesting topic worth studying. Yin et al. used gold nanoparticles to modify the surfaces of poly (styrene-acrylic acid) nanospheres, which served as a matrix to conjugate alkaline phosphatase to detect the tumor necrosis factor α [28]. Zhang et al. modified glassy carbon electrodes with silver nanoparticle–poly (trans-3-(3-pyridyl) acrylic acid) -MWNTs–COOH for the detection of DNA [29]. Most signals output from sensors in biomedical detection were electric signals, which reflected the concentration of the target substrate and the catalytic performance of the sensing materials. Stoichiometry is considered to be an effective method for sensing signal analysis. Esteban et al. indicated that stoichiometric tools can be applied to electroanalytical data obtained from sensors, and they are very helpful for multianalyte calibration and modelling in multicomponent dynamic systems [30].

The studies mentioned above are all applications of metallic nanomaterials used in biomedical sensing. However, in practice, the acquisition of sensing data in biomedical detection depends on the design of the sensor device—for example, whether the sensor is small enough to be implanted into the human body, whether the sensor is flexible enough to fit the skin or epidermis, whether the sensor substrate is stable enough to hold the sensing element, and whether the sensor is biocompatible. Meanwhile, the challenges of biological toxicity brought by metallic nanomaterials also need to be overcome [31]. Therefore, it is desirable to develop biological sensing devices with excellent performance to resolve the problems mentioned above. In addition, it is also necessary to study the specific problems in detail first and then put forward a strategy. Some directions of metallic nanomaterials applied in biomedical sensing are summarized in Figure 1, which can provide some ideas to researchers who are interested in this Special Issue.

2. Contributions

This Special Issue is dedicated to works related to metallic nanomaterials with biomedical applications. The scope includes, but is not limited to, the following topics: the synthesis and characterization of metallic nanomaterials; metallic nanomaterial-based electrochemical sensors and biosensors; metallic oxide-modified electrodes; biological sensing based on metallic nanomaterials; chemometrics for metallic nanomaterial-based biological sensing; and metallic nanomaterial-based biological sensing devices.