Enhanced photoelectrochemical property of ZnO nanorods array synthesized on reduced graphene oxide for self-powered biosensing application

Red and near-infrared light-activated photoelectrochemical nanobiosensors for biomedical target detection

Photoelectrochemical (PEC) nanobiosensors integrate molecular (bio)recognition elements with semiconductor/plasmonic photoactive nanomaterials to produce measurable signals after light-induced reactions. Recent advancements in PEC nanobiosensors, using light-matter interactions, have significantly improved sensitivity, specificity, and signal-to-noise ratio in detecting (bio)analytes. Tunable nanomaterials activated by a wide spectral radiation window coupled to electrochemical transduction platforms have further improved detection by stabilizing and amplifying electrical signals. This work reviews PEC biosensors based on nanomaterials like metal oxides, carbon nitrides, quantum dots, and transition metal chalcogenides (TMCs), showing their superior optoelectronic properties and analytical performance for the detection of clinically relevant biomarkers. Furthermore, it highlights the innovative role of red light and NIR-activated PEC nanobiosensors in enhancing charge transfer processes, protecting them from biomolecule photodamage in vitro and in vivo applications. Overall, advances in PEC detection systems have the potential to revolutionize rapid and accurate measurements in clinical diagnostic applications. Their integration into miniaturized devices also supports the development of portable, easy-to-use diagnostic tools, facilitating point-of-care (POC) testing solutions and real-time monitoring.

Carbon-based photoelectrochemical sensors: recent developments and future prospects

Owing to the considerable potential of photoelectrochemical (PEC) sensors, they have gained significant attention in the analysis of biological, environmental, and food markers. However, the limited charge mass transfer efficiency and rapid recombination of electron hole pairs have become obstacles in the development of PEC sensors. In this case, considering the unique advantages of carbon-based materials, they can be used as photosensitizers, supporting materials and conductive substrates and coupled with semiconductors to prepare composite materials, solving the above problems. In addition, there are many types of carbon materials, which can have semiconductor properties and form heterojunctions after coupling with semiconductors, effectively promoting the separation of electron hole pairs. Herein, we aimed to provide a comprehensive analysis of reports on carbon-based PEC sensors by introducing their research and application status and discussing future development trends in this field. In particular, the types and performance improvement strategies of carbon-based electrodes and the working principles of carbon-based PEC sensors are explained. Furthermore, the applications of carbon-based photoelectric sensors in environmental monitoring, biomedicine, and food detection are highlighted. Finally, the current limitations in the research on carbon-based PEC sensors are emphasized and the need to enhance the sensitivity and selectivity through material modification, structural design, improved device performance, and other strategies are emphasized.

Lung cancer cells detection by a photoelectrochemical MoS2 biosensing chip

This research aims to explore the potential application of this approach in the production of biosensor chips. The biosensor chip is utilized for the identification and examination of early-stage lung cancer cells. The findings of the optical microscope were corroborated by the field emission scanning electron microscopy, which provided further evidence that the growth of MoS2 is uniform and that there is minimal disruption in the electrode, hence minimizing the likelihood of an open circuit creation. Furthermore, the bilayer structure of the produced MoS2 has been validated through the utilization of Raman spectroscopy. A research investigation was undertaken to measure the photoelectric current generated by three various types of clinical samples containing lung cancer cells, specifically the CL1, NCI-H460, and NCI-H520 cell lines. The findings from the empirical analysis indicate that the coefficient of determination (R-Square) for the linear regression model was approximately 98%. Furthermore, the integration of a double-layer MoS2 film resulted in a significant improvement of 38% in the photocurrent, as observed in the device's performance.

Ultra-sensitive photoelectrochemical sensor for copper ion detection based on ITO/BiVO4 photoelectrode

In this work, a photoelectrochemical sensor for Cu2+ trace detection was prepared based on the excellent semiconductor material BiVO4 modified ITO electrode. It was found that Cu2+ formed a doping effect by adsorption on the surface of ITO/BiVO4 electrode, which inhibited the photogenerated electron complex and thus caused an increase in photocurrent. In addition, due to the complexation effect of EDTA on Cu2+, the Cu2+ adsorbed on the electrode surface is desorbed and the photocurrent returns to the blank value, making it possible to reuse electrodes. Under optimal conditions, the linearity range was measured between 0.1 pM and 0.1 μM and the detection limit was 0.063 pM. The PEC sensor exhibits the advantages of high sensitivity and reusability for Cu2+ detection. This provides a novel PEC detection platform for Cu2+ monitoring in environmental water samples.

Recent Progress in Interface Engineering of Nanostructures for Photoelectrochemical Energy Harvesting Applications

With rapid and continuous consumption of nonrenewable energy, solar energy can be utilized to meet the energy requirement and mitigate environmental issues in the future. To attain a sustainable society with an energy mix predominately dependent on solar energy, photoelectrochemical (PEC) device, in which semiconductor nanostructure-based photocatalysts play important roles, is considered to be one of the most promising candidates to realize the sufficient utilization of solar energy in a low-cost, green, and environmentally friendly manner. Interface engineering of semiconductor nanostructures has been qualified in the efficient improvement of PEC performances including three basic steps, i.e., light absorption, charge transfer/separation, and surface catalytic reaction. In this review, recently developed interface engineering of semiconductor nanostructures for direct and high-efficiency conversion of sunlight into available forms (e.g., chemical fuels and electric power) are summarized in terms of their atomic constitution and morphology, electronic structure and promising potential for PEC applications. Extensive efforts toward the development of high-performance PEC applications (e.g., PEC water splitting, PEC photodetection, PEC catalysis, PEC degradation and PEC biosensors) are also presented and appraised. Last but not least, a brief summary and personal insights on the challenges and future directions in the community of next-generation PEC devices are also provided.

Disposable solar microcell array-based addressable photoelectrochemical sensor for high-throughput and multiplexed analysis of salivary metabolites

The high-throughput detection of multiple metabolites in saliva by electrochemical sensors is usually a challenge, which however is essential to the comprehensive evaluation of health status or screening of diseases. Here, a light-addressable and paper-based hydrogen peroxide (H₂O₂) photoelectrochemical (PEC) sensor for the high-throughput detection of multiple salivary metabolites is reported. This sensor has a unique solar microcell array structure with a silver nanowires/fullerene-Congo red (AgNWs/C₆₀-CR) disc working electrode (WE) and a single-walled carbon nanotubes/platinum nanowires (SWCNTs/PtNWs) ring reference/counter electrode (RE/CE) in each microcell. Enzymes of different metabolites are immobilized on different separated microcells of a cover slide over the sensor, from which enzymatically produced H₂O₂ can react with p-hydroxyphenyl boric acid (4-HPBA) on the WE of the sensor to generate hydroquinone (HQ) for photocurrent responses. Based on this strategy, a disposable PEC sensor of saliva was developed, which allows the multiplexed detection of uric acid (UA), glucose (GLU) and lactate (LA) in diluted human saliva with high sensitivity and selectivity. Moreover, the detection throughput and application field of the sensor can be easily extended by connecting a series of sensors in parallel or varying the enzymes. The present work thus establishes a cost-effective approach to the scalable construction of versatile biosensing platforms with tunable throughput and varied analytes.

Research trends in biomedical applications of two-dimensional nanomaterials over the last decade - A bibliometric analysis

Two-dimensional (2D) nanomaterials with versatile properties have been widely applied in the field of biomedicine. Despite various studies having reviewed the development of biomedical 2D nanomaterials, there is a lack of a study that objectively summarizes and analyzes the research trend of this important field. Here, we employ a series of bibliometric methods to identify the development of the 2D nanomaterial-related biomedical field during the past 10 years from a holistic point of view. First, the annual publication/citation growth, country/institute/author distribution, referenced sources, and research hotspots are identified. Thereafter, based on the objectively identified research hotspots, the contributions of 2D nanomaterials to the various biomedical subfields, including those of biosensing, imaging/therapy, antibacterial treatment, and tissue engineering are carefully explored, by considering the intrinsic properties of the nanomaterials. Finally, prospects and challenges have been discussed to shed light on the future development and clinical translation of 2D nanomaterials. This review provides a novel perspective to identify and further promote the development of 2D nanomaterials in biomedical research.

High-Efficiency Crystalline Silicon-Based Solar Cells Using Textured TiO2 Layer and Plasmonic Nanoparticles

A high-efficiency crystalline silicon-based solar cell in the visible and near-infrared regions is introduced in this paper. A textured TiO₂ layer grown on top of the active silicon layer and a back reflector with gratings are used to enhance the solar cell performance. The given structure is simulated using the finite difference time domain (FDTD) method to determine the solar cell’s performance. The simulation toolbox calculates the short circuit current density by solving Maxwell’s equation, and the open-circuit voltage will be calculated numerically according to the material parameters. Hence, each simulation process calculates the fill factor and power conversion efficiency numerically. The optimization of the crystalline silicon active layer thickness and the dimensions of the back reflector grating are given in this work. The grating period structure of the Al back reflector is covered with a graphene layer to improve the absorption of the solar cell, where the periodicity, height, and width of the gratings are optimized. Furthermore, the optimum height of the textured TiO₂ layer is simulated to produce the maximum efficiency using light absorption and short circuit current density. In addition, plasmonic nanoparticles are distributed on the textured surface to enhance the light absorption, with different radii, with radius 50, 75, 100, and 125 nm. The absorbed light energy for different nanoparticle materials, Au, Ag, Al, and Cu, are simulated and compared to determine the best performance. The obtained short circuit current density is 61.9 ma/cm², open-circuit voltage is 0.6 V, fill factor is 0.83, and the power conversion efficiency is 30.6%. The proposed crystalline silicon solar cell improves the short circuit current density by almost 89% and the power conversion efficiency by almost 34%.

Addressable Label-Free Photoelectric Sensor Array with Self-Calibration for Detection of Neuron Specific Enolase

An addressable label-free photoelectric immunosensor array was designed for detection of neuron specific enolase (NSE) based on TiO₂/CdS as substrate materials. In this work, the hydrothermal synthesized TiO₂ nanorod film is evenly grown on the surface of the fluorine-doped tin oxide (FTO), and then CdS with a narrow band gap is added for sensitization through successive ionic layer adsorption reactions. The obtained TiO₂/CdS composite materials with matched energy band structures promote the rapid electron transfer and effectively reduce the recombination of electron hole pairs, which greatly enhance the visible light absorption and increased photocurrent intensity. In order to construct a suitable sensor array, the sensitized FTO electrode is divided into multiple regions of equal size by insulating stickers, and then the addressable and continuous detection of multiple samples can be achieved. Because multiple detection regions are prepared and tested under the same conditions, the difference effectively reduces, and the sensor can realize self-calibration and obtain more accurate results. Under optimal conditions, this sensor array can detect NSE in the linear range of 0.01-100 ng mL^-1 with a detection limit of 2.49 pg mL^-1 (S/N = 3). The sensor array has good selectivity, stability, and reproducibility, making it a viable approach for real sample detection.

InSe:Ge-doped InSe van der Waals heterostructure to enhance photogenerated carrier separation for self-powered photoelectrochemical-type photodetectors

Two-dimensional (2D) van der Waals (vdW) materials with tunable heterostructures and superior optoelectronic properties have opened a new platform for various applications, e.g., field-effect transistors, ultrasensitive photodetectors and photocatalysts. In this work, an InSe/InSe(Ge) (germanium doped InSe) vdW heterostructure is designed to improve the photoresponse performance of sole InSe in a photoelectrochemical (PEC)-type photodetector. Photoelectrochemical measurements demonstrated that this heterostructure has excellent photoresponse characteristics, including a photocurrent density of 9.8 μA cm^-2, a photo-responsivity of 64 μA W^-1, and a response time/recovery time of 0.128 s/0.1 s. Moreover, the measurements also revealed the self-powering capability and long-term cycling stability of this heterostructure. The electronic properties of the prepared pure and Ge-doped single crystals unveiled a negative and temperature-independent thermoelectric power and temperature-activated resistivity. The negative character of dominating charge carriers was confirmed by Hall measurements, which corroborated by electrical resistivity revealed a carrier concentration below ∼10¹⁵ cm^-3 and an electron mobility of ∼500 cm² V^-1 s^-1 in Ge-doped crystals. Additionally, the Mott-Schottky model explored the mechanism of charge transfer and enhanced PEC performance. Band bending at the InSe/InSe(Ge)-electrolyte interface benefits the separation and transformation of photogenerated carriers from the heterostructure to electrolyte due to the tunable energy band alignment. These results indicate that the InSe/InSe(Ge) vdW heterostructure is promising for PEC-type photodetectors, which provide a novel way to utilize 2D vdW heterostructures in optoelectronics.

Light Harvesting in Silicon Nanowires Solar Cells by Using Graphene Layer and Plasmonic Nanoparticles

In this work, a silicon nanowire solar cell for efficient light harvesting in the visible and near-infrared regions is introduced. In this structure, the silicon nanowires (SiNWs) are coated with a graphene layer and plasmonic nanoparticles are distributed on the top surface of the silicon substrate layer. The proposed structure is simulated using the finite difference time domain (FDTD) method to determine the performance of the solar cell by calculating the open-circuit voltage, fill factor, short-circuit current density, and power conversion efficiency. The absorbed light energy is compared for different nanoparticle materials, namely Au, Ag, Al, and Cu, and Au NPs give the best performance. Different values of the radius of the Au NP are simulated, namely 30, 40, 50, and 60 nm, to determine the optimum radius, and the effect of excess carrier concentration on the solar cell performance is also tested. The obtained open-circuit voltage is 0.63 V, fill factor is 0.73, short-circuit current density is 41.7 mA/cm2, and power conversion efficiency is 19.0%. The proposed SiNW solar cell improves the overall efficiency by almost 60%. Furthermore, the effects of the NW length and distance between NWs are also studied in this work. Finally, the distribution of the optical power in different layers along the solar cell and for different solar cell structures is also illustrated in this paper.

High Performance Polymer Solar Cells Using Grating Nanostructure and Plasmonic Nanoparticles

This work introduces a high-efficiency organic solar cell with grating nanostructure in both hole and electron transport layers and plasmonic gold nanoparticles (Au NPs) distributed on the zinc oxide (ZnO) layer. The periods of the grating structure in both hole and electro transport layers were optimized using Lumerical finite difference time domain (FDTD) solution software. The optimum AuNP radius distributed on the ZnO layer was also simulated and analyzed before studying the effect of changing the temperature on the solar cell performance, fill factor, and power conversion efficiency. In addition, optical and electrical models were used to calculate the short circuit current density, fill factor, and overall efficiency of the produced polymer solar cell nanostructure. The maximum obtained short circuit current density and efficiency of the solar cell were 18.11 mA/cm² and 9.46%, respectively, which gives a high light absorption in the visible region. Furthermore, the effect of light polarization for incident light angles from θ = 0° to 70° with step angle 10° on the electrical and optical parameters were also studied. Finally, optical power, electric field, and magnetic field distribution inside the nanostructure are also illustrated.

Borosilicate glasses containing CdS/ZnS QDs: A heterostructured composite with enhanced degradation of IC dye under visible-light

The glass system SiO₂-B₂O₃-Na₂O₃-ZnO containing 2 wt% CdS and 1 wt% ZnS was synthesized by the conventional melt quench method. Glass transition temperature and crystallization temperature was determined from Differential thermal analysis (DTA) measurement to optimize heat-treatment. The amorphous structure of the glass was confirmed by the X-ray diffraction (XRD) measurement. Glasses were heat-treated by optimized heat-treatment schedule to grow CdS/ZnS QDs and crystalline phases of CdS and ZnS were confirmed by the XRD measurement. High-Resolution Transmission Electron Microscopy (HRTEM) was used to determine the size and shape of quantum dots (QDs) grown in the glass matrix. The optical band gap was calculated from the absorption spectra and found to decrease with increase in size of QDs. Electron-hole recombination rate was studied using a decay time and impedance analyzer. Prepared samples were tested as a photocatalyst under sunlight for the degradation of indigo carmine (IC) dye and photodegradation efficiency was found to be 73.6 % and 87.2 % for samples CZ1 and CZ4 respectively. No significant change is observed in degradation efficiency even for 4 cycles which confirms the stability of prepared glasses for dye degradation.

A photoelectrochemical sensor for glutathione based on Bi2S3-modified TiO2 nanotube arrays

A novel photoelectrochemical sensor for the determination of glutathione based on Bi2S3-modified TiO2 nanotube arrays. Under the excitation of visible light, glutathione can be oxidized by the holes created by the Bi2S3/TiO2 NTAs.

Characteristics of P-Type and N-Type Photoelectrochemical Biosensors: A Case Study for Esophageal Cancer Detection

P-type and N-type photoelectrochemical (PEC) biosensors were established in the laboratory to discuss the correlation between characteristic substances and photoactive material properties through the photogenerated charge carrier transport mechanism. Four types of human esophageal cancer cells (ECCs) were analyzed without requiring additional bias voltage. Photoelectrical characteristics were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–vis reflectance spectroscopy, and photocurrent response analyses. Results showed that smaller photocurrent was measured in cases with advanced cancer stages. Glutathione (L-glutathione reduced, GSH) and Glutathione disulfide (GSSG) in cancer cells carry out redox reactions during carrier separation, which changes the photocurrent. The sensor can identify ECC stages with a certain level of photoelectrochemical response. The detection error can be optimized by adjusting the number of cells, and the detection time of about 5 min allowed repeated measurement.

Aptamer-functionalized metal-organic frameworks (MOFs) for biosensing

As a class of crystalline porous materials, metal-organic frameworks (MOFs) have attracted increasing attention. Due to the nanoscale framework structure, adjustable pore size, large specific surface area, and good chemical stability, MOFs have been applied widely in many fields such as biosensors, biomedicine, electrocatalysis, energy storage and conversions. Especially when they are combined with aptamer functionalization, MOFs can be utilized to construct high-performance biosensors for numerous applications ranging from medical diagnostics and food safety inspection, to environmental surveillance. Herein, this article reviews recent innovations of aptamer-functionalized MOFs-based biosensors and their bio-applications. We first briefly introduce different functionalization methods of MOFs with aptamers, which provide a foundation for the construction of MOFs-based aptasensors. Then, we comprehensively summarize different types of MOFs-based aptasensors and their applications, in which MOFs serve as either signal probes or signal probe carriers for optical, electrochemical, and photoelectrochemical detection, with an emphasis on the former. Given recent substantial research interests in stimuli-responsive materials and the microfluidic lab-on-a-chip technology, we also present the stimuli-responsive aptamer-functionalized MOFs for sensing, followed by a brief overview on the integration of MOFs on microfluidic devices. Current limitations and prospective trends of MOFs-based biosensors are discussed at the end.

A one-step hydrothermal route to fabricate a ZnO nanorod/3D graphene aerogel-sensitized structure with enhanced photoelectrochemistry performance and self-powered photoelectrochemical biosensing of parathion-methyl

A facile one-pot hydrothermal method for fabricating ZnO/GAs was developed. And a novel self-powered PEC biosensor was constructed based on the ZnO/GAs with the amplification of thiocholine for the detection of parathion-methyl.

Preparation of PbS NPs/RGO/NiO nanosheet arrays heterostructure: Function-switchable self-powered photoelectrochemical biosensor for H2O2 and glucose monitoring

On the basis of synthesized PbS nanoparticles (PbS NPs)/reduced graphene oxide (RGO)/NiO nanosheet arrays (NiO NSAs) heterostructure, we constructed a function-switchable self-powered PEC sensing platform for the analysis of H2O2 and glucose. Ordered NiO NSAs have high electron mobility, modifying RGO onto the surfaces of NiO NSAs can connect the NiO NSAs with the PbS NPs and promoted the electron transfer rate between them, as well as enhance their photocurrent response. The PbS NPs/RGO/NiO NSAs heterostructure own excellent catalase-like activity can achieve H2O2 detection, only with one more step, after introducing glucose oxidase (GOD) onto the surface of PbS NPs/RGO/NiO NSAs heterostructure, we realized the detection conversion between H2O2 and glucose. Under optimal conditions, the proposed biosensor exhibited superior analytical performance toward H2O2 and glucose, a limit of detection (LOD) of 0.018 mM (S/N = 3) and 5.3 × 10-8 M (S/N = 3) were obtained, respectively. Moreover, good accuracy was obtained in the real samples analysis of H2O2 disinfectant and human serum samples.

Electron Acceptors Co-Regulated Self-Powered Photoelectrochemical Strategy and Its Application for Circulating Tumor Nucleic Acid Detection Coupled with Recombinase Polymerase Amplification

Biosensor working in a self-powered mode has been widely concerned because it produces a signal when the bias potential is 0 V. However, the self-powered mode is used only when the materials have self-powered properties. Conversion of non-self-powered to self-powered through molecular regulation can solve this problem effectively. Here, we fabricated a self-powered photoelectrochemical mode based on co-regulation of electron acceptors methylene blue (MB) and p-nitrophenol (p-NP). AuNPs@ZnSe nanosheet-modified gold electrode (AuNPs@ZnSeNSs/GE) gave a small photocurrent at 0 V. In the presence of MB and p-NP, AuNPs@ZnSeNSs/GE gave the strongest photocurrent at 0 V. Accordingly, an electron acceptor co-regulated self-powered photoelectrochemical assay was fabricated. As proof-of-concept demonstrations, this assay was applied for prostate cancer circulating tumor nucleic acid biomarker, KLK2 and PCA3, detection combined with in situ recombinase polymerase amplification strategy. This assay generated a strong photocurrent and was sensitive to the variation of KLK2 and PCA3 concentration. The limits of detection were 30 and 32 aM, respectively. We anticipate this electron acceptor co-regulated self-powered photoelectrochemical mode to pave a new way for the development of self-powered sensing.

Cu2O/PEDOT:PSS/ZnO Nanocomposite Material Biosensor for Esophageal Cancer Detection

A highly sensitive photoelectrochemical (PEC) biosensor without external bias was developed in this study. The biosensor was configured with a p-Cu₂O and n-ZnO heterostructure. Hexamethylenetetramine (HMTA) and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) was used to improve the crystal structure of Cu₂O and ZnO and reduce the defects in the Cu₂O/ZnO interface. This fabrication method provided the highly crystallized Cu₂O/ZnO structure with excellent electrical property and photoresponse in visible light. The structure was applied to a biosensor for detecting two different cancerous levels of esophageal cells, namely, OE21 and OE21-1, with a high gain in photocurrent (5.8 and 6.2 times, respectively) and a low detection limit (3000 cells in 50 μL). We believe that such a p-n heterojunction PEC biosensor could advance biosensor development and provide a promising candidate for biomedical applications.

ZnO-reduced graphene oxide composite based photoelectrochemical aptasensor for sensitive Cd(II) detection with methylene blue as sensitizer

In this paper a photoelectrochemical (PEC) aptasensor based on specific recognition with conformational changed after the target Cd(II) identification was fabricated. A ZnO and reduced graphene oxide (ZnO-rGO) nanocomposite with enhanced PEC activity was designed as photoactive material. After the further incorporation of gold nanoparticles (AuNPs) with ZnO-rGO nanocomposite, the enhanced photocurrent signal could be detected owing to the localized surface plasmon resonance and good conductivity of AuNPs. In addition, AuNPs were used as anchors for immobilization of -SH modified aptamer S1. After that aptamer S2 was paired with S1 sequence to form complementary double stranded DNA (dsDNA) on the electrode surface. Methylene blue (MB) was acted as sensitizer and assembled in dsDNA structure to amplify photocurrent response. When Cd(II) was bound to the aptamer presented on the sensing interface, S2 specifically recognized and captured Cd(II), which resulted in the unwinding of dsDNA structure and the separation of MB molecules from the electrode surface with photocurrent response decreased. The photocurrent was detected by a double-working-electrode system, which used the modified electrode as the first working electrode and glassy carbon electrode (GCE) as the second working electrode. Dopamine (DA) was added to the electrolyte and acted as the electron donor, which could be oxidized on the modified electrode and reduced on the GCE to form a cyclic reaction, leading to the enhanced photocurrent response with improved photocurrent stability. This MB sensitized PEC aptasensor exhibited a high sensitivity with a detection limit of 1.8 × 10^-12 mol/L (3σ). Thus, a highly sensitive aptasensor with double-working-electrode detection method for Cd(II) determination were established and further applied to the water samples analysis.

Platinum and Iridium Oxide Co-modified TiO2 Nanotubes Array Based Photoelectrochemical Sensors for Glutathione

Oriented TiO₂ nanotubes, which are fabricated by anodic oxidation method, are prospective in photoelectrochemical analysis and sensors. In this work, Pt and IrO₂ co-modified TiO₂ nanotubes array was prepared via a two-step deposition process involving the photoreductive deposition of Pt and chemical deposition of IrO₂ on the oriented TiO₂ nanotubes. Due to the improved separation of photo-generated electrons and holes, Pt-IrO₂ co-modified TiO₂ nanotubes presented significantly higher PEC activity than pure TiO₂ nanotubes or mono-modified TiO₂ nanotubes. The PEC sensitivity of Pt-IrO₂ co-modified TiO₂ nanotubes for glutathione was also monitored and good sensitivity was observed.

Photo-driven self-powered biosensor for ultrasensitive microRNA detection via DNA conformation-controlled co-sensitization behavior

We developed a photoelectrochemical enzymatic fuel cell-based self-powered biosensing platform for microRNA detection via DNA conformation change-controlled co-sensitization behavior.

Nanoporous gold electrode for ultrasensitive detection of neurotoxin fasciculin

Acetylcholinesterase (AChE), an efficient biocatalyst known to hydrolyze the neurotransmitter acetylcholine, could be inactivated in the presence of insecticides, nerve agents or other drug inhibitors to thus result in disrupted neurotransmission. Improvement in the peripheral cholinergic function, as well as overall cognition and neuronal functions of an exposed system could be achieved if the mechanisms of inhibitions are deactivated in a controlled fashion and with rapid response time. Herein, we proposed to develop a simple AChE biosensor capable to realize the rapid detection of neurotoxins. Our approach uses a nanoporous gold film (NPGF) and reduced graphene oxide-tin dioxide nanoparticle (RGO-SnO₂) nanocomposite to define the highly active electrode interface where the electrochemical monitoring of the interaction between AChE and its target molecule, fasciculin, could take place. Our results demonstrate that the established biosensor had the ability to monitor fasciculin concentrations at the ultra-low limit of detection of 8 pM, an inhibition rate of 8% and within only 30min of electrochemical exposure. Our study provides a convenient technology for the rapid and ultrasensitive detection of neurotoxins and has the potential for large applicability to other drugs or toxins screening.

Preparation and characterization of 0D Au NPs@3D BiOI nanoflower/2D NiO nanosheet array heterostructures and their application as a self-powered photoelectrochemical biosensing platform

In this work, we demonstrate that zero-dimensional Au nanoparticles (0D Au NPs)-decorated three-dimensional bismuth oxyiodide (BiOI) nanoflower (3D BiOI NFs)/two-dimensional nickel oxide (NiO) nanosheet array (2D NiO NSAs) hybrid nanostructures can be used as a self-powered cathodic photoelectrochemical (PEC) biosensing platform. The in situ formation of 3D BiOI NFs on 2D NiO NSAs was carried out by a chemical bath deposition method, while 0D Au NPs were coated on 3D BiOI NFs/2D NiO NSAs through a dip-coating method. Subsequently, glucose oxidase (GOD) as an enzyme model was immobilized on the surface of a Au@BiOI/NiO electrode via the adhesion of poly-(diallyldimethylammonium chloride) (PDDA). The proposed heterostructure exhibited excellent PEC properties because the unique structure of the Au NPs@BiOI NFs/NiO NSAs increased the specific surface area, light harvesting ability and the surface plasmon resonance effect of the Au NPs. The system displayed high sensitivity toward glucose in the presence of an air-saturated electrolyte. At the optimum conditions, the biosensor showed a promising application for the self-powered cathodic PEC biosensing of glucose, with a dynamic linear range of 1 × 10^-7 M to 5 × 10^-2 M and a low limit of detection of 8.71 × 10^-8 M. Moreover, the proposed self-powered PEC biosensor was evaluated for the determination of diluted glucose injections, with the results indicating the potential of the proposed biosensor for bioanalysis applications.

CdS quantum dots/Au nanoparticles/ZnO nanowire array for self-powered photoelectrochemical detection of Escherichia coli O157:H7

In this paper, the hydrothermally grown ZnO nanowire array (NWs) was modified by Au nanoparticles (NPs) and CdS quantum dots (QDs) to construct a high-performance photoelectrochemical (PEC) electrode. The aligned ZnO NWs, which decorated Au NPs and CdS QDs have the effective light absorption range from UV to visible region. This hybrid structure provided a self-powered PEC electrode with a favorable energy-band configuration for fast charge separation and transportation. Meanwhile, the Au NPs and CdS QDs also made increase of the surface area to improve the immobilization of the analytes. After assembling aptamer as recognition element, this composite nanoarray was further developed as a self-powered PEC biosensor by synergizing above multiple enhancement factors. The PEC aptasensor exhibited a rapid response in a wide linear range of 10-10⁷ CFU/mL with the detection limit as low as 1.125 CFU/mL to Escherichia coli O157:H7 (E. coli O157:H7). This approach would offer an alternative PEC transduction for fast environment monitoring and clinical diagnosis related to pathogenic bacteria.

Enhanced photoelectric conversion efficiency: A novel h-BN based self-powered photoelectrochemical aptasensor for ultrasensitive detection of diazinon

This work presents a novel hexagonal boron nitride (h-BN) based self-powered photoelectrochemical (PEC) aptasensor for ultrasensitive detection of diazinon (DZN) with excellent photoelectric conversion efficiency. It was the first time that h-BN based materials were applied to PEC aptasensor, in which the construction of Z-scheme heterojunction of h-BN and graphitic carbon nitride (CN) via doping sulfur into h-BN was innovatively proposed. Meanwhile, Au nanoparticles (AuNPs) were utilized for the surface plasmon resonance (SPR) effect and the formation of new recombination centers. The charge transfer mechanism was expounded and verified by the electron spin resonance (ESR) spin-trap technique. The proposed PEC aptasensor for determination of DZN exhibited a wide linear range from 0.01 to 10000 nM and a low detection limit of 6.8 pM with superb selectivity and remarkable stability. Moreover, the constructed PEC aptasensor performed well with excellent recoveries in three different real samples. This work illustrated that PEC aptasensor is a promising alternative to conventional analytical technologies for the detection of DZN and other organophosphorus (OP) pesticides. The designing ideas of the proposed h-BN based material can provide a foothold for the innovative construction of photoactive materials for PEC bioanalysis.

One-pot synthesis of a CdS-reduced graphene oxide-carbon nitride composite for self-powered photoelectrochemical aptasensing of PCB72

Graphitic carbon nitride (C3N4) is a carbon-based metal-free semiconductor, which has been widely explored as a photoactive material. In this work, the CdS, reduced graphene oxide (rGO) and C3N4 (CdS-rGO-C3N4) composite was synthesized by a simple one-pot hydrothermal method and utilized to construct a photoelectrochemical (PEC) sensor. Compared with CdS, C3N4 and CdS-C3N4, the CdS-rGO-C3N4 composite exhibited enhanced photoelectrochemical (PEC) performance, due to the expanded absorption of C3N4 in the visible region by CdS and promoted the charge carrier separation of a photoelectrode by rGO. Based on a glassy carbon electrode (GCE) modified with CdS-rGO-C3N4 and a PCB72-binding aptamer (ap/CdS-rGO-C3N4/GCE), a PEC aptasensor for the detection of 2,3',5,5'-tetrachlorobiphenyl (PCB72) was developed. When H2O2 was added into the electrolyte, the PEC sensor exhibited an amplified response toward PCB72, and could be operated in a self-powered mode at a potential of 0 V. Under optimum conditions, the constructed PEC aptasensor exhibited a wide linear range of 10 to 1000 ng mL-1 for PCB72 detection, with a low detection limit (S/N = 3) of 1.0 ng mL-1. Moreover, this aptasensor exhibited high selectivity, good reproducibility and high stability. The applicability of the developed PEC strategy was demonstrated by determining PCB72 in environmental water.

Recent Advances in Biosensors Based Nanostructure for Pharmaceutical Analysis

Background:

The development of novel nanostructures for pharmaceutical analysis has received great attention. Biosensors are a class of analytical techniques competent in the rapid quantification of drugs. Recently, the nanostructures have been applied for modification of biosensors.

Objective:

The goal of the present study is to review novel nanostructures for pharmaceutical analysis by biosensors.

Method:

In this review, the application of different biosensors was extensively discussed.

Results:

Biosensors based nanostructures are a powerful alternative to conventional analytical techniques, enabling highly sensitive, real-time, and high-frequency monitoring of drugs without extensive sample preparation. Several examples of their application have been reported.

Conclusion:

The present paper reviews the recent advances on the pharmaceutical analysis of biosensor based nanostructures.

Electrophoretically Deposited MoSe2/WSe2 Heterojunction from Ultrasonically Exfoliated Nanocrystals for Enhanced Electrochemical Photoresponse

The solar response ability and low-cost fabrication of the photoanode are important factors for the effective output of the photoelectrochemical system. Modification of the photoanode by which its ability to absorb irradiation can be manipulated has gained tremendous attention. Here, we demonstrated the MoSe₂, WSe₂, and MoSe₂/WSe₂ nanocrystal thin films prepared by the liquid-phase exfoliated and electrophoresis methods. Atomic force microscopy and high-resolution transmission electron microscopy show that the liquid exfoliated nanocrystals have a few layered dimensions with good crystallinity. Scanning electron microscopy demonstrated uniform distribution and randomly oriented nanocrystals, having a homogeneous shape and size. X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectra confirm the equal contribution of MoSe₂ and WSe₂ nanocrystals in the formation of the MoSe₂/WSe₂ heterojunction. Because of superior absorption of MoSe₂/WSe₂ heterojunction in the visible region and type-II heterojunction band alignment, in situ measurement of heterojunction electrode shows almost 1.5 times incident photo-to-current conversion efficiency and photoresponsivity in comparison to individual material electrodes. Our result clearly indicates the influence of heterojunction formation between liquid exfoliated nanocrystals on effective separation of photogenerated exciton and enhances charge carrier transfer, which leads to the improvement in photoelectrochemical performance. Liquid exfoliated nanosheet-based heterojunction is attractive as efficient photoanodes for the photoelectrochemical systems.

Photostable 3D heterojunction photoanode made of ZnO nanosheets coated onto TiO2 nanowire arrays for photoelectrochemical solar hydrogen generation

Applications of single-phase TiO₂ and ZnO in the field of photoelectrochemical (PEC) solar hydrogen generation are limited by their high recombination rate of photogenerated charge carriers.

SERS-Active 3D Interconnected Nanocarbon Web toward Nonplasmonic in Vitro Sensing of HeLa Cells and Fibroblasts

A noninvasive intracellular component analysis technique is important in cancer treatment and the initial identification of cancer. Carbon nanomaterials/nanostructures, such as carbon nanotubes and graphene, have little to no surface enhanced Raman scattering (SERS) ability. Because of these structures' low Raman responses, they are conjugated with gold or silver to attain the SERS-active ability to detect normal fibroblasts and HeLa cancer cells. To the best of our knowledge, the effectiveness of the individual use of carbon nanomaterials as a nonplasmonic SERS-active platform for in vitro cancer/normal cell detection has not been investigated to date. Here, for the first time, we introduce a unique nonplasmonic SERS-based biosensing platform that uses a biocompatible self-assembled three-dimensional interconnected nanocarbon web (INW) for in vitro detection and differentiation of HeLa cells and fibroblasts. The sub-10-nm morphology of the INW facilitates the endocytic uptake of INW clusters to the cells, and its SERS functionality introduces live cell Raman sensing. The INW platform has achieved an enhancement factor (EF) of 3.66 × 10⁴ and 9.10 × 10³ with crystal violet and Rhodamine 6G dyes, respectively, significant in comparison to the EF of graphene surfaces (2-17). The results of the time-based Raman spectroscopy of live HeLa cells and fibroblasts revealed chemical fingerprints of intracellular components, such as DNA/RNA, proteins, and lipids. The components' spectroscopic differences facilitate and elucidate the specification of each cell. The highest Raman enhancement achieved was fourfold for fibroblasts (protein) and sixfold for HeLa cells (DNA). Furthermore, the SERS spectra along with scanning electron microscopy and fluorescence microscopy analysis of the immobilized cells after 24 and 48 h shed light on the health of fibroblasts and HeLa cells. A photon energy-induced ionization achieved with a femtosecond laser fabricated a biocompatible INW platform with the designated unique attributes. This simple, label-free, in vitro diagnosis approach for HeLa cells and fibroblasts has strong potential for cancer research.

Co3O4/carbon composite nanofibrous membrane enabled high-efficiency electromagnetic wave absorption

Electromagnetic (EM) wave absorbing materials have been fabricated from diverse materials such as conductive polymers, carbon based nanostructures and magnetic metal oxides. Nevertheless, it has remained a great challenge to develop lightweight and high-efficiency EM wave absorbing materials with a broad frequency range. Herein, we report a scalable strategy to create Co₃O₄/carbon composite nanofibrous membrane by electrospinning technique followed by stabilization and carbonization processes. An optimal reflection loss (R_L) value of 36.27 dB is reached at 13.76 GHz for a layer of 2 mm thickness. RL exceeding −20 dB can be realized in any interval within the 4.5–14.4 GHz range by selecting a proper thickness of the absorbing layer between 1 and 5 mm. The Co₃O₄/carbon composite nanofibrous membrane could be well served as promising and attractive candidates for lightweight and enhanced EM wave absorbing materials. This presented research provides an innovative and effective approach to design the novel EM wave absorbing material in a broad frequency range for practical applications.

RuO2/graphene nanoribbon composite supported on screen printed electrode with enhanced electrocatalytic performances toward ethanol and NADH biosensing

In this work, we aimed to propose a newly synthesized composite material with enhanced electrocatalytic properties as a novel screen-printed sensor for the quantification of NADH. Additionally, the surface was modified with alcohol dehydrogenase for the preparation of an amperometric biosensor for analysis of ethanol. Synthesized material was characterized using several microstructural (FE-SEM, HR-TEM, XRD) and electrochemical (CV, EIS) techniques. The electrochemical response of the tested analytes was investigated as a function of important parameters. Under optimal conditions, the working linear range and limit of detection for ethanol sensing was 1-1800 µM and 0.19 µM, respectively. For NADH, the linear range was from 1 to 1300 µM with limit of detection of 0.52 µM. Moreover, effects of some possible interfering compounds were investigated and the developed procedure was applied to commercial alcoholic beverages. The results obtained showed satisfactory precision and accuracy of the developed method and confirm the proposed approach could be a possible replacement for the currently used techniques for ethanol and NADH quantification.

Highly sensitive glucose sensor based on monodisperse palladium nickel/activated carbon nanocomposites

Glucose enzyme biosensors have been used for a variety of applications such as medical diagnosis, bioprocess engineering, beverage industry and environmental scanning etc. and there is still a growing interest in glucose sensors. For this purpose, addressed herein, as a novel glucose sensor, highly sensitive activated carbon (AC) decorated monodisperse nickel and palladium alloy nanocomposites modified glassy carbon electrode (Ni-Pd@AC/GCE NCs) have been synthesized by in-situ reduction technique. Raman Spectroscopy (RS), X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), cyclic voltammetry (CV) and chronoamperometry (CA) were used for the characterization of the prepared non-enzymatic glucose sensor. The characteristic sensor properties of the Ni-Pd@AC/GCE electrode were compared with Ni-Pd NCs/GCE, Ni@AC/GCE and Pd@AC/GCE and the results demonstrate that the AC is very effective in the enhancement of the electrocatalytic properties of sensor. In addition, the Ni-Pd@AC/GCE nanocomposites showed a very low detection limit of 0.014 μM, a wide linear range of 0.01 mM-1 mM and a very high sensitivity of 90 mA mM^-1 cm^-2. Furthermore, the recommended sensor offer the various advantageous such as facile preparation, fast response time, high selectivity and sensitivity. Lastly, monodisperse Ni-Pd@AC/GCE was utilized to detect glucose in real sample species.

Structural modulation of CdS/ZnO nanoheterojunction arrays for full solar water splitting and their related degradation mechanisms

Higher PEC performance for full water splitting was realized for a CoPi–CdS/ZnO NHA via structural modulation, and degradation in the performance was elucidated.

3D graphene foam/ZnO nanorods array mixed-dimensional heterostructure for photoelectrochemical biosensing

We combined a 3D graphene foam network with a ZnO NRs array and further introduced this mixed-dimensional heterostructure into a PEC biosensing system.

Reduced graphene oxide/BiFeO3 nanohybrids-based signal-on photoelectrochemical sensing system for prostate-specific antigen detection coupling with magnetic microfluidic device

A novel magnetic controlled photoelectrochemical (PEC) sensing system was designed for sensitive detection of prostate-specific antigen (PSA) using reduced graphene oxide-functionalized BiFeO₃ (rGO-BiFeO₃) as the photoactive material and target-triggered hybridization chain reaction (HCR) for signal amplification. Remarkably enhanced PEC performance could be obtained by using rGO-BiFeO₃ as the photoelectrode material due to its accelerated charge transfer and improved the visible light absorption. Additionally, efficient and simple operation could be achieved by introducing magnetic controlled flow-through device. The assay mainly involved in anchor DNA-conjugated magnetic bead (MB-aDNA), PSA aptamer/trigger DNA (Apt-tDNA) and two glucose oxidase-labeled hairpins (H1-GOx and H2-GOx). Upon addition of target PSA, the analyte initially reacted with the aptamer to release the trigger DNA, which partially hybridized with the anchor DNA on the MB. Thereafter, the unpaired trigger DNA on the MB opened the hairpin DNA structures in sequence and propagated a chain reaction of hybridization events between two alternating hairpins to form a long nicked double-helix with numerous GOx enzymes on it. Subsequently, the enzymatic product (H₂O₂) generated and consumed the photo-excited electrons from rGO-BiFeO₃ under visible light irradiation to enhance the photocurrent. Under optimal conditions, the magnetic controlled PEC sensing system exhibited good photocurrent responses toward target PSA within the linear range of 0.001 - 100ng/mL with a detection limit of 0.31pg/mL. Moreover, favorable selectivity, good stability and satisfactory accuracy were obtained. The excellent analytical performance suggested that the rGO-BiFeO₃-based PEC sensing platform could be a promising tool for sensitive, efficient and low cost detection of PSA in disease diagnostics.