Photoelectrochemical Enzyme Biosensor Based on TiO2 Nanorod/TiO2 Quantum Dot/Polydopamine/Glucose Oxidase Composites with Strong Visible-Light Response

Vertical graphene nanoarray decorated with Ag nanoparticles exhibits enhanced antibacterial effects

Bacterial infection of biomedical implants is an important clinical challenge, driving the development of novel antimicrobial materials. The antibacterial effect of vertically aligned graphene as a nanoarray coating has been reported. In this study, vertically aligned graphene nanosheets decorated with silver nanoparticles were fabricated to enhance antibacterial effectiveness. Vertical graphene (VG) nanoflakes were synthesized by plasma-enhanced chemical vapor deposition (PECVD). Ag nanoparticles were attached to the surface of VG through using polydopamine and achieving a sustained release of Ag+. VG loaded with Ag nanoparticles (VGP/Ag) not only prevented bacterial adhesion for a long time, but also exhibited good biocompatibility. This work provides a new venue for designing antibacterial surfaces based on combination of graphene nanoarrays with other nanomaterials, and the results indicate that this approach could be very successful in preventing implant associated infections.

Enhancement in Sensitivity and Selectivity of Electrochemical Technique with CuO/g-C3N4 Nanocomposite Combined with Molecularly Imprinted Polymer for Melamine Detection

This study focused on enhancing the sensitivity and selectivity to detect melamine by utilizing a photoelectrochemical method. This was achieved by combining a melamine-imprinted polymer with a CuO/g-C3N4 nanocomposite, which was synthesized through chemical precipitation and calcination. The resulting nanocomposite exhibits improved carrier mobility and photoelectrochemical properties. A molecularly imprinted receptor for selective detection was created through bulk polymerization with methacrylic acid and a melamine template. The characterization of the nanocomposite was performed using X-ray photoelectron spectroscopy for the chemical oxidation state, X-ray diffraction patterns for the crystalline structure, and ultraviolet/visible/near-infrared spectroscopy for optical properties. The CuO/g-C3N4 nanocomposite exhibits photoactivity under visible light. The modified electrode, incorporating the CuO/g-C3N4 nanocomposite and melamine-imprinted polymer, demonstrates a linear detection range of 2.5 to 50 nM, a sensitivity of 4.172 nA/nM for melamine, and a low detection limit of 0.42 nM. It shows good reproducibility and high selectivity to melamine, proving effective against interferences and real samples, showcasing the benefits of the molecularly imprinted polymer.

Bi2WO6/TiO2-based visible light-driven photoelectrochemical enzyme biosensor for glucose measurement

Nowadays, the frequent occurrence of food adulteration makes glucose detection particularly important in food safety and quality management. The quality and taste of honey are closely related to the glucose content. However, due to the drawbacks of expensive equipment, complex operating procedures, and time-consuming processes, the application scope of traditional glucose detection methods is limited. Hence, this study developed a photoelectric chemical (PEC) sensor, which is composed of a photoactive material of bismuth tungstate (Bi2WO6) with titanium dioxide (TiO2) and glucose oxidase (GOD), for simple and rapid detection of glucose. Notably, the composites' absorption prominently increased in the visible light region, and the photo-generated electron-hole pairs were efficiently separated by virtue of the unique nanostructure system, thus playing a crucial role in facilitating PEC activity. In the presence of dissolved oxygen, the photocurrent intensity was enhanced by H2O2 generated from glucose under electro-oxidation specifically catalyzed by GOD fixed on the modified electrode. When the working potential was 0.3 V, the changes of photocurrent response indicated that the PEC enzyme biosensor provides a low detection limit (3.8 µM), and a wide linear range (0.008-8 mM). This method has better selectivity in honey samples and broad application prospects in clinical diagnosis for future.

CdSe/TiO2NTs Heterojunction-Based Nonenzymatic Photoelectrochemical Sensor for Glucose Detection

Compared with a single semiconductor, the heterojunction formed by two different semiconductors usually has higher light utilization and better photoelectric performance. By using stable TiO2 nanotubes as the main subject, CdSe/TiO2NTs heterojunctions were synthesized by a hydrothermal method. XRD, TEM, SEM, PL, UV-vis, and EIS were used to characterize the fabricated CdSe/TiO2NTs. Under visible light irradiation, CdSe/TiO2NTs heterojunctions exhibited a higher absorption intensity and lower degree of photogenerated carrier recombination than TiO2. The electrons and holes were proven to be effectively separated in this heterojunction via theoretical calculation. Under CdSe/TiO2NTs' optimal conditions, the glucose concentrations (10-90 μM) had a linear relationship with the photocurrent value, and the detection limit was 3.1 μM. Moreover, the CdSe/TiO2NTs sensor exhibited good selectivity and stability. Based on the experimental data and theoretical calculations, its PEC sensing mechanism was also illuminated.

Antibacterial Activity of PVA Hydrogels Embedding Oxide Nanostructures Sensitized by Noble Metals and Ruthenium Dye

Nanostructured oxides (SiO2, TiO2) were synthesized using the sol-gel method and modified with noble metal nanoparticles (Pt, Au) and ruthenium dye to enhance light harvesting and promote the photogeneration of reactive oxygen species, namely singlet oxygen (1O2) and hydroxyl radical (•OH). The resulting nanostructures were embedded in a transparent polyvinyl alcohol (PVA) hydrogel. Morphological and structural characterization of the bare and modified oxides was performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), UV-Vis spectroscopy, and X-ray photoelectron spectroscopy (XPS). Additionally, electrokinetic potential measurements were conducted. Crystallinity data and elemental analysis of the investigated systems were obtained through X-ray diffraction and X-ray fluorescence analyses, while the chemical state of the elements was determined using XPS. The engineered materials, both as simple powders and embedded in the hydrogel, were evaluated for their ability to generate reactive oxygen species (ROS) under visible and simulated solar light irradiation to establish a correlation with their antibacterial activity against Staphylococcus aureus. The generation of singlet oxygen (1O2) by the samples under visible light exposure can be of significant importance for their potential use in biomedical applications.

High-performance Vo-ZnO/ZnS benefiting nanoarchitectonics from the synergism between defect engineering and surface engineering for photoelectrochemical glucose sensors

In this study, a ZnO/ZnS nanocluster heterojunction photoelectrode rich in surface oxygen defects (Vo-ZnO/ZnS) was prepared by applying a simple in situ anion substitution and nitrogen atmosphere annealing method. The synergism between defect and surface engineering significantly improved the photocatalysts. Given this synergism, Vo-ZnO/ZnS was endowed with a long carrier lifetime, narrow band gap, high carrier density, and high performance toward electron transfer under light conditions. Thus, Vo-ZnO/ZnS had three times the photocurrent density of ZnO under light illumination. To further evaluate its advantages in the field of photoelectric bioassay, Vo-ZnO/ZnS was applied as the photocathode of photoelectric sensor system for glucose detection. Vo-ZnO/ZnS showed excellent performance in glucose detection in various aspects, including a low detection limit, high detection sensitivity, and a wide detection range.

Semiconductor quantum dots in photoelectrochemical sensors from fabrication to biosensing applications

Semiconductor quantum dots (QDs) are a promising class of nanomaterials for developing new photoelectrodes and photoelectrochemistry systems for energy storage, transfer, and biosensing applications. These materials have unique electronic and photophysical properties and can be used as optical nanoprobes in displays, biosensors, imaging, optoelectronics, energy storage and energy harvesting. Researchers have recently been exploring the use of QDs in photoelectrochemical (PEC) sensors, which involve exciting a QD-interfaced photoactive material with a flashlight source and generating a photoelectrical current as an output signal. The simple surface properties of QDs also make them suitable for addressing issues related to sensitivity, miniaturization, and cost-effectiveness. This technology has the potential to replace current laboratory practices and equipment, such as spectrophotometers, used for testing sample absorption and emission. Semiconductor QD-based PEC sensors offer simple, fast, and easily miniaturized sensors for analyzing a variety of analytes. This review summarizes the various strategies for interfacing QD nanoarchitectures for PEC sensing, as well as their signal amplification. PEC sensing devices, particularly those used for the detection of disease biomarkers, biomolecules (glucose, dopamine), drugs, and various pathogens, have the potential to revolutionize the biomedical field. This review discusses the advantages of semiconductor QD-based PEC biosensors and their fabrication methods, with a focus on disease diagnostics and the detection of various biomolecules. Finally, the review provides prospects and considerations for QD-based photoelectrochemical sensor systems in terms of their sensitivity, speed, and portability for biomedical applications.

Colorimetric Sensors for Chemical and Biological Sensing Applications

Colorimetric sensors have been widely used to detect numerous analytes due to their cost-effectiveness, high sensitivity and specificity, and clear visibility, even with the naked eye. In recent years, the emergence of advanced nanomaterials has greatly improved the development of colorimetric sensors. This review focuses on the recent (from the years 2015 to 2022) advances in the design, fabrication, and applications of colorimetric sensors. First, the classification and sensing mechanisms of colorimetric sensors are briefly described, and the design of colorimetric sensors based on several typical nanomaterials, including graphene and its derivatives, metal and metal oxide nanoparticles, DNA nanomaterials, quantum dots, and some other materials are discussed. Then the applications, especially for the detection of metallic and non-metallic ions, proteins, small molecules, gas, virus and bacteria, and DNA/RNA are summarized. Finally, the remaining challenges and future trends in the development of colorimetric sensors are also discussed.

On the Use of Polymer-Based Composites for the Creation of Optical Sensors: A Review

Polymers are widely used in many areas, but often their individual properties are not sufficient for use in certain applications. One of the solutions is the creation of polymer-based composites and nanocomposites. In such materials, in order to improve their properties, nanoscale particles (at least in one dimension) are dispersed in the polymer matrix. These properties include increased mechanical strength and durability, the ability to create a developed inner surface, adjustable thermal and electrical conductivity, and many others. The materials created can have a wide range of applications, such as biomimetic materials and technologies, smart materials, renewable energy sources, packaging, etc. This article reviews the usage of composites as a matrix for the optical sensors and biosensors. It highlights several methods that have been used to enhance performance and properties by optimizing the filler. It shows the main methods of combining indicator dyes with the material of the sensor matrix. Furthermore, the role of co-fillers or a hybrid filler in a polymer composite system is discussed, revealing the great potential and prospect of such matrixes in the field of fine properties tuning for advanced applications.

Engineering exposed vertical nano-TiO2 (001) facets/BiOI nanosheet heterojunction film for constructing a satisfactory PEC glucose oxidase biosensor

In the field of photoelectrochemical (PEC) enzyme biosensors, constructing efficient photoelectrodes, in which the recombination of photogenerated carriers is an important factor affecting the performance, is of great significance. Herein, to enhance the separation efficiency of photogenerated carriers, titanium dioxide (TiO₂) nanosheet (NS)/bismuth oxyiodide (BiOI) NS/glucose oxidase (GOx) composites were prepared via hydrothermal and solvothermal methods. Single-crystal anatase TiO₂ NSs with a high percentage of (001) facets lead to better photocarrier separation due to heterojunctions between facets. After coupling with BiOI NSs, the photoelectrochemical performance of the electrode was greatly improved. The photogenerated electrons from TiO₂ and BiOI gathered at TiO₂ (101) and were exported through the fluorine-doped tin oxide (FTO) substrate to generate electrical signals. Photogenerated holes were transferred to TiO₂ (001) and BiOI to participate in the enzymatic reaction, showing the outstanding separation of electrons and holes. The prepared TiO₂ NS/BiOI NS/GOx glucose biosensor achieved satisfactory results, with sensitivity of 14.25 μA mM⁻¹ cm⁻², a linear measurement range of 0–1 mM, and a limit of detection (3S/N) of 0.01 mM in phosphate buffered saline (PBS) at a pH of 7.4. The mechanism for the efficient separation of photogenerated carriers based on the facet heterojunctions introduced in this paper also provides new insights into other optoelectronic biosensors.

Demonstration of the mechanism based on the synergistic effect of TiO₂ facet heterojunctions and TiO₂/BiOI heterojunctions to promote efficient separation of photogenerated carriers.

Nano-Scaled Materials and Polymer Integration in Biosensing Tools

The evolution of biosensors and diagnostic devices has been thriving in its ability to provide reliable tools with simplified operation steps. These evolutions have paved the way for further advances in sensing materials, strategies, and device structures. Polymeric composite materials can be formed into nanostructures and networks of different types, including hydrogels, vesicles, dendrimers, molecularly imprinted polymers (MIP), etc. Due to their biocompatibility, flexibility, and low prices, they are promising tools for future lab-on-chip devices as both manufacturing materials and immobilization surfaces. Polymers can also allow the construction of scaffold materials and 3D structures that further elevate the sensing capabilities of traditional 2D biosensors. This review discusses the latest developments in nano-scaled materials and synthesis techniques for polymer structures and their integration into sensing applications by highlighting their various structural advantages in producing highly sensitive tools that rival bench-top instruments. The developments in material design open a new door for decentralized medicine and public protection that allows effective onsite and point-of-care diagnostics.