Self-powered photoelectrochemical aptasensor for fumonisin B1 detection based on a Z-scheme ZnIn2S4/WO3 photoanode

The incidence of esophageal cancer is positively associated with fumonisin contamination. It is necessary to develop methods for the rapid detection of fumonisins. In this work, a self-powered photoelectrochemical aptamer sensor based on ZnIn2S4/WO3 photoanode and Au@W-Co3O4 photocathode is proposed for the sensitive detection of fumonisin B1 (FB1). Among them, under visible light irradiation, the Z-type heterostructure of ZnIn2S4/WO3 acts as a photoanode to improve the electron transfer rate, which contributes to the enhancement of the photocathode signal and lays the foundation for a wider detection range. The Au@W-Co3O4 photocathode as a sensing interface reduces the probability of false positives (comparison of anode sensing platforms). The PEC sensor has a good working performance in the detection range (10 pg/mL-1000 ng/mL) with a detection limit of 2.7 pg/mL (S/N = 3). In addition, the sensor offers good selectivity, stability and excellent recoveries in real sample analysis. This work is expected to play a role in the field of analyzing environmental toxins.

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.

β-Ga2O3nanotube arrays for high-performance self-powered ultraviolet photoelectrochemical photodetectors

Self-powered ultraviolet (UV) photodetectors (PDs) are critical for future energy-efficient optoelectronic systems due to their low energy consumption and high sensitivity. In this paper, the vertically alignedβ-Ga2O3nanotube arrays (NTs) have been prepared on GaN/sapphire substrate by the thermal oxidation process combined with the dry etching technology, and applied in the UV photoelectrochemical photodetectors (PEC-PDs) for the first time. Based on the large specific surface area ofβ-Ga2O3NTs on GaN/sapphire substrates and the solid/liquid heterojunction, the PEC-PDs exhibit excellent self-powered characteristics under 255 nm (UVA) and 365 nm (UVC) light illumination. Under 255 nm (365 nm) light illumination, the maximum responsivity of 49.9 mA W-1(32.04 mA W-1) and a high detectivity of 1.58 × 1011Jones (1.01 × 1011Jones) were achieved for theβ-Ga2O3NTs photodetectors at 0 V bias. In addition, the device shows a fast rise/decay time of 8/4 ms (4/2 ms), which is superior to the level of the previously reported self-powered UV PEC-PDs. This high-performance PEC-PD has potential applications in next-generation low-energy UV detection systems.

Recent Progress in Photoelectrochemical Sensing of Pesticides in Food and Environmental Samples: Photoactive Materials and Signaling Mechanisms

Pesticides have become an integral part of modern agricultural practices, but their widespread use poses a significant threat to human health. As such, there is a pressing need to develop effective methods for detecting pesticides in food and environmental samples. Traditional chromatography methods and common rapid detection methods cannot satisfy accuracy, portability, long storage time, and solution stability at the same time. In recent years, photoelectrochemical (PEC) sensing technology has gained attention as a promising approach for detecting various pesticides due to its salient advantages, including high sensitivity, low cost, simple operation, fast response, and easy miniaturization, thus becoming a competitive candidate for real-time and on-site monitoring of pesticide levels. This review provides an overview of the recent advancements in PEC methods for pesticide detection and their applications in ensuring food and environmental safety, with a focus on the categories of photoactive materials, from single semiconductor to semiconductor-semiconductor heterojunction, and signaling mechanisms of PEC sensing platforms, including oxidation of pesticides, steric hindrance, generation/decrease in sacrificial agents, and introduction/release of photoactive materials. Additionally, this review will offer insights into future prospects and confrontations, thereby contributing novel perspectives to this evolving domain.

Photoelectrochemical Sensor with a Z-Scheme Fe2O3/CdS Heterostructure for Sensitive Detection of Mercury Ions

Mercury (Hg2+) is a highly toxic element and can seriously affect human health. This work proposed a photoelectrochemical (PEC) sensor with a Z-scheme Fe2O3/CdS heterostructure and two thymine-rich DNA strands (DNA-1 and Au@DNA-2) for sensitive detection of Hg2+. The light excitation of the Fe2O3/CdS composite accelerated the electron transfer among Fe2O3, CdS, and the electrode to produce a stable photocurrent response. Upon the recognition of Hg2+ to thymine bases (T) in two DNA strands to form a stable T-Hg2+-T biomimetic structure, the photocurrent response increased with the increasing concentration of Hg2+ due to the opening of electronic transmission channels from Au nanoparticles to Fe2O3/CdS nanocomposite. Under the optimal conditions screened by the Box-Behnken experiments, the proposed PEC sensor showed excellent analytical performance for Hg2+ detection with high sensitivity, a detection limit of 0.20 pM at a signal-to-noise ratio of 3, high selectivity, a detectable concentration range of 1 pM-100 nM, and acceptable stability. The good recovery and low relative standard deviation for the analysis of Hg2+ in lake and tap water samples demonstrated the potential application of the designed Z-scheme Fe2O3/CdS heterostructure in the PEC detection of heavy metal ions.

Nanozyme-assisted ratiometric photoelectrochemical aptasensor over Cu2O nanocubes mediated photocurrent-polarity-switching based on S-scheme FeCdS@FeIn2S4 heterostructure

The controllable modulation of the response mode is highly attractive for the construction of photoelectrochemical (PEC) sensors with improved sensitivity and anti-interference ability in complex real samples matrix. Here, we present a charming proof-of-concept ratiometric PEC aptasensor of enrofloxacin (ENR) analysis via the controllable signal transduction. Different with the traditional sensing mechanism, this ratiometric PEC aptasensor integrates the anodic PEC signal induced by PtCuCo nanozyme-catalyzed precipitation reaction and the polarity-switching cathodic PEC response mediated by Cu2O nanocubes on S-scheme FeCdS@FeIn2S4 heterostructure. Taking advantages of the photocurrent-polarity-switching signal response model and the superior performance of the photoactive substrate material, the proposed ratiometric PEC aptasensor displays a good detection linear range for ENR analysis from 0.01 pg mL-1 to 10 ng mL-1, with a detection limit of 3.3 fg mL-1. This study provides a general platform for detecting interested trace analytes in real samples and expands the diversity of sensing strategy design.

Light-driven uranyl-organic frameworks used as signal-enhanced photoelectrochemical sensors for monitoring anthrax

The semiconductor-like characteristics and light absorption ability of metal-organic frameworks (MOFs) make it have the potential for photoelectrochemical sensing. Compared with composite and modified materials, the specific recognition of harmful substances directly using MOFs with suitable structures can undoubtedly simplify the fabrication of sensors. Herein, two photosensitive uranyl-organic frameworks (UOFs) named HNU-70 and HNU-71 were synthesized and explored as the novel "turn-on" photoelectrochemical sensors, which can be directly applied to monitor the biomarker of anthrax (dipicolinic acid). Both sensors have good selectivity and stability towards dipicolinic acid with the low detection limits of 1.062 and 1.035 nM, respectively, which are far lower than the human infection concentration. Moreover, they exhibit good applicability in the real physiological environment of human serum, demonstrating a good application prospect. Spectroscopic and electrochemical studies show that the mechanism of photocurrent enhancement results from the interaction between dipicolinic acid and UOFs, which facilitates the photogenerated electron transport.

A novel signal amplification strategy for label-free electrochemical DNA sensor based on the interaction between α-cyclodextrin and ferrocenyl indicator

The synthesized ferrocene appended naphthalimide derivative (FND) exhibited great binding ability toward dsDNA, while its usage as the electrochemical hybridization indicator was restricted by the poor water solubility. Herein, a simple and effective signal amplification strategy for FND based label-free DNA biosensors was developed based on the interaction between FND and cyclodextrin. α-Cyclodextrin (α-CD), β-cyclodextrin (β-CD) and γ-cyclodextrin (γ-CD) were helpful to amplify the signal of the DNA biosensor, while the signal amplification effect of α-CD was better than that of β-CD and γ-CD. Under the optimum conditions, there was a 3-fold increase in the sensitivity of the DNA biosensor after the addition of α-CD. The interaction between FND and α-/β-/γ-CD was investigated by differential pulse voltammetry and fluorescence experiment. Experimental results showed that α-CD not only minimized the impact on the electrochemical activity of FND but also improved the dispersity of FND in aqueous solution. That was why the proposed biosensor showed higher sensitivity in the presence of α-CD. This strategy was universal for other ferrocenyl indicators with similar structures as used in this work.

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.

2D carbon materials based photoelectrochemical biosensors for detection of cancer antigens

Cancer is a leading cause of death globally and early diagnosis is of paramount importance for identifying appropriate treatment pathways to improve cancer patient survival. However, conventional methods for cancer detection such as biopsy, CT scan, magnetic resonance imaging, endoscopy, X-ray and ultrasound are limited and not efficient for early cancer detection. Advancements in molecular technology have enabled the identification of various cancer biomarkers for diagnosis and prognosis of the deadly disease. The detection of these biomarkers can be done by biosensors. Biosensors are less time consuming compared to conventional methods and has the potential to detect cancer at an earlier stage. Compared to conventional biosensors, photoelectrochemical (PEC) biosensors have improved selectivity and sensitivity and is a suitable tool for detecting cancer agents. Recently, 2D carbon materials have gained interest as a PEC sensing platform due to their high surface area and ease of surface modifications for improved electrical transfer and attachment of biorecognition elements. This review will focus on the development of 2D carbon nanomaterials as electrode platform in PEC biosensors for the detection of cancer biomarkers. The working principles, biorecognition strategies and key parameters that influence the performance of the biosensors will be critically discussed. In addition, the potential application of PEC biosensor in clinical settings will also be explored, providing insights into the future perspective and challenges of exploiting PEC biosensors for cancer diagnosis.

Photoelectrochemical Immunosensor Based on a 1D Fe2O3/3D Cd-ZnIn2.2Sy Heterostructure as a Sensing Platform for Ultrasensitive Detection of Neuron-Specific Enolase

Lung cancer is a high-mortality cancer related to the concentration of neuron-specific enolase (NSE). In this work, a sandwich-type photoelectrochemical (PEC) immunosensor was constructed for ultrasensitive detection of NSE, which is based on iron trioxide/indium zinc cadmium sulfide (Fe₂O₃/Cd-ZnIn_2.2S_y) as a sensing platform and Ag-modified polyaniline (Ag@PANI) as a signal amplification label. The 1D Fe₂O₃ porous nanorods with a large specific surface area were synthesized by calcination of Fe-MIL-88A and etching of NaOH. To improve the photocurrent response, the 3D architecture Cd-ZnIn_2.2S_y was combined with the 1D Fe₂O₃ porous nanorods to form a 1D Fe₂O₃/3D Cd-ZnIn_2.2S_y heterostructure. Specifically, the Fe₂O₃/Cd-ZnIn_2.2S_y heterostructure with a good energy level matching (the two can form a stepped energy level matching, which accelerates the transfer rate of electrons) can improve the separation efficiency of electron-hole pairs (e^-/h⁺) under visible light irradiation, which enhances the photocurrent response. Ag@PANI has a strong electron transport capability and can be used as a secondary antibody marker for the signal amplification of the immunosensor. The sensor exhibits a good linear detection range of 100 fg/mL to 100 ng/mL with a low detection limit of 33.5 fg/mL. Moreover, the constructed sandwich-type PEC immunosensor shows good performance and possesses excellent specificity, selectivity, and stability over a period of 4 weeks for NSE detection. With these excellent properties, the immunosensor can be extended to analyze and diagnose other disease biomarkers.

Nanozyme-based sensors for detection of food biomarkers: a review

Nanozymes have piqued the curiosity of scientists in recent years because of their ability to demonstrate enzyme-like activity combined with advantages such as high stability, inexpensive availability, robust activity, and tunable properties. These attributes have allowed the successful application of nanozymes in sensing to detect various chemical and biological target analytes, overcoming the shortcomings of conventional detection techniques. In this review, we discuss recent developments of nanozyme-based sensors to detect biomarkers associated with food quality and safety. First, we present a brief introduction to this topic, followed by discussing the different types of sensors used in food biomarker detection. We then highlight recent studies on nanozyme-based sensors to detect food markers such as toxins, pathogens, antibiotics, growth hormones, metal ions, additives, small molecules, and drug residues. In the subsequent section, we discuss the challenges and possible solutions towards the development of nanozyme-based sensors for application in the food industry. Finally, we conclude the review by discussing future perspectives of this field towards successful detection and monitoring of food analytes.

Homogeneous photoelectrochemical biosensor for sensitive detection of omethoate via ALP-mediated pesticide assay and Bi2S3@Bi2Sn2O7 heterojunction as photoactive material

A simple homogeneous photoelectrochemical (PEC) sensing platform based on an alkaline phosphatase (ALP)-mediated pesticide assay was established for the sensitive detection of omethoate (OM). The Bi₂S₃@Bi₂Sn₂O₇ heterojunction was used as a photoactive material to provide stable background photocurrent signals. The inhibition of OM on ALP and PEC determination was carried out in the homogeneous system. In the absence of OM, dephosphorylation of L-ascorbic acid 2-phosphate trisodium salt (AAP) was catalyzed by ALP to produce the enzyme-catalyzed product (L-ascorbic acid, AA). AA, as an electron donor, could capture photogenerated holes on the Bi₂S₃@Bi₂Sn₂O₇ heterojunction, thus inhibiting the recombination of electron holes to achieve an increase of the photocurrent signal. When the OM was introduced, the enzyme activity of ALP was reduced due to the organophosphorus pesticides (OPs)-based enzyme inhibition, and the AA produced by catalytic hydrolysis was also reduced, thus reducing the photocurrent signal. Compared with the traditional PEC sensor for OPs, this homogeneous PEC sensor avoided immobilization procedures, covalent labeling, separation, and the steric hindrance effect caused by immobilized biomolecules, which achieved high recognition efficiency and caused a reduction in analysis time. Additionally, an ALP-mediated pesticide assay for the determination of OPs with a simplified experimental process further improved the stability and reproducibility of the PEC sensor. The PEC sensor showed high sensitivity to the target OM within a dynamic range of 0.05 ~ 500 ng mL^-1, and the detection limit was 0.0146 ng mL^-1. Additionally, the PEC biosensing system showed good selectivity and anti-interference ability, and exhibited a satisfactory result in spinach and mustard samples. A homogeneous PEC biosensor based on ALP inhibition strategy was constructed for OM detection in vegetable samples via Bi₂S₃@Bi₂Sn₂O₇ heterojunction as the photoactive substrate material.

Enhanced Ultrasensitive Photoelectrochemical Probe for Phosphate Detection in Water Based on a Zirconium-Porphyrin Framework

Excessive phosphate poses a serious ecological and human health risk, and thereby, monitoring its trace concentration is of great significance to environmental protection and human health. In this work, a zirconium-porphyrin framework (PCN-222) with excellent stability and unique luminescence properties was designed to modify the surface of the indium tin oxide electrode, which was first used as a photoelectrochemical (PEC) probe for phosphate detection. The PCN-222-modified PEC probe demonstrated an excellent selectivity and stability and indicated a linear response to phosphate in the range of 0-10⁶ nM with a limit of detection (LOD) as low as 1.964 nM. To the best of our knowledge, this is the phosphate probe with the lowest LOD, and this is also the first signal-on PEC probe toward phosphate based on PCN-222. More importantly, the PEC probe can be validated for the good applicability of trace phosphate detection in real water samples, indicating a good application prospect. Finally, a series of electrochemical and spectroscopic studies have proved that phosphate can bind to the indium tin oxide (ITO)/PCN-222 electrode, which shortens the distance of the space charge region while reducing the bandwidth and thus facilitates the transfer of photogenerated electrons across the energy band barrier to reduce O₂ in the electrolyte, producing an enhanced cathodic photocurrent signal. The proposed strategy of the highly sensitive PEC probe provides a promising platform for more effective label-free phosphate monitoring in the environment and organisms.

Surface Plasmon-Enhanced Photoelectrochemical Sensor Based on Au Modified TiO2 Nanotubes

Based on the enhanced charge separation efficiency of the one-dimensional structure and strong surface plasmon resonance (SPR) of gold, a gold modified TiO₂ nanotube (Au/TiO₂NTs) glucose photoelectrochemical (PEC) sensor was prepared. It could be activated by visible red light (625 nm). Under optimal conditions, the Au/TiO₂NTs sensor exhibited a good sensitivity of 170.37 μA·mM⁻¹·cm⁻² in the range of 1–90 μM (R² = 0.9993), and a detection limit of 1.3 μM (S/N = 3). Due to its high selectivity, good anti-interference ability, and long-term stability, the fabricated Au/TiO₂NTs sensor provides practical detection of glucose. It is expected to be used in the construction of non-invasive PEC biosensors.

Dual-Engine Powered Paper Photoelectrochemical Platform Based on 3D DNA Nanomachine-Mediated CRISPR/Cas12a for Detection of Multiple miRNAs

This work proposed a novel double-engine powered paper photoelectrochemical (PEC) biosensor based on an anode-cathode cooperative amplification strategy and various signal enhancement mechanisms, which realized the monitoring of multiple miRNAs (such as miRNA-141 and miRNA-21). Specifically, C₃N₄ quantum dots (QDs) sensitized ZnO nanostars and BiOI nanospheres simultaneously to construct a composite photoelectric layer that amplified the original photocurrent of the photoanode and photocathode, respectively. Through the independent design and partition of a flexible paper chip to functionalize injection holes and electrode areas, the bipolar combination completed the secondary upgrade of signals, which also provided biological reaction sites for multitarget detection. With the synergistic participation of a three-dimensional (3D) DNA nanomachine and programmable CRISPR/Cas12a shearing tool, C₃N₄ QDs lost their attachment away from the electrode surface to quench the signal. Moreover, electrode zoning significantly reduced the spatial cross talk of related substances for multitarget detection, while the universal trans-cleavage capability of CRISPR/Cas12a simplified the operation. The designed PEC biosensor revealed excellent linear ranges for detection of miRNA-141 and miRNA-21, for which the detection limits were 5.5 and 3.4 fM, respectively. With prominent selectivity and sensitivity, the platform established an effective approach for trace multitarget monitoring in clinical applications, and its numerous pioneering attempts owned favorable reference values.

Detection of NSE by a photoelectrochemical self-powered immunosensor integrating RGO photocathode and WO3/Mn:CdS nanomaterial photoanode

Generally, the photoanodic photoelectrochemical (PEC) immunoassay method has an outstanding photocurrent and low detection limit, but its poor anti-interference ability in the detection of real samples restricts its performance. The photocathode immunoassay method has an excellent ability to see interference in actual sample detection, but it has its own defect in that the photocurrent is not obvious. Here, a promising new cathodic PEC immunosensing platform is reported, which integrates a photocathode and photoanode. The photoanode and photocathode are WO₃/Mn:CdS composite modified and reduced graphene oxide (RGO) modified indium tin oxide (ITO) electrodes, respectively. In addition to an excellent PEC response, the immunosensor constructed by the integrating the photoanode and photocathode also has good anti-interference ability in actual sample analysis. The constructed immunosensor achieves accurate detection of NSE with a range from 5.0 pg/mL to 20 ng/mL, and the limit of detection (LOD) is 1.2 pg/mL. The proposed immunoassay method has good stability, selectivity and reproducibility. Moreover, it introduces new ideas for the construction of PEC immunosensors.

Organic β-cyclodextrin Nanoparticle: An Efficient Building Block Between Functionalized Poly(pyrrole) Electrodes and Enzymes

Glyconanoparticles (GNPs) made by self-assembly of carbohydrate-based polystyrene-block-β-cyclodextrin copolymer are used as a building block for the design of nanostructured biomaterials of electrode. The firm immobilization of GNPs is carried out on electrochemically generated polymer, poly(pyrrole-adamantane), and copolymer, poly(pyrrole-adamantane)/poly(pyrrole-lactobionamide) via host-guest interactions between adamantane and β-cyclodextrin. The ability of GNPs for the specific anchoring of biological macromolecules is investigated using glucose oxidase enzyme modified by adamantane groups as a protein model (GOx-Ad). The immobilization of GOx-Ad is carried out by incubation of an aqueous enzyme solution on a coating of GNPs adsorbed on a platinum electrode. The presence of immobilized GOx-Ad is evaluated in aqueous glucose solution by potentiostating the underlying platinum electrode at 0.7 V/SCE for the electro-oxidation of H₂ O₂ generated by the enzyme. The analytical performance of the bioelectrodes for the detection of glucose is compared to control electrodes prepared without GNPs or without electropolymerized films. The better permeability of copolymer compared to polymer and the possibility to elaborate two alternating layers of GNPs and GOx-Ad are clearly observed. The best amperometric response is recorded with a multilayered bioelectrode displaying a wide linear range linear range of the calibration curve: 68 µmol L^-1 to 0.1 mol L^-1 .

Recent advances in electron manipulation of nanomaterials for photoelectrochemical biosensors

This feature article discusses the recent advances and strategies of building photoelectrochemical (PEC) biosensors from the perspective of regulating the electron transfer of nanomaterials.

High-sensitivity and versatile plasmonic biosensor based on grain boundaries in polycrystalline 1L WS2 films

Structural defects play an important role in exploitation of two-dimensional layered materials (2DLMs) for advanced biosensors with the increasingly high sensitivity and low detection limit. Grain boundaries (GBs), as an important type of structural defect in polycrystalline 2DLM films, potentially provide sufficient active defect sites for the immobilization of bioreceptor units via chemical functionalization. In this work, we report the selective functionalization of high-density GBs with complementary DNA receptors, via gold nanoparticle (AuNP) linkers, in wafer-scale polycrystalline monolayer (1L) W(Mo)S₂ films as versatile plasmonic biosensing platforms. The large surface area and GB-rich nature of the polycrystalline 1L WS₂ film enabled the immobilization of bioreceptors in high surface density with spatial uniformity, while the AuNPs perform not only as bioreceptor linkers, but also promote detection sensitivity through surface plasmon resonance enhancement effect. Therefore, the presented biosensor demonstrated highly sensitive and selective sub-femto-molar detection of representative RNA sequences from the novel coronavirus (RdRp, ORF1ad and E). This work demonstrates the immense potential of AuNP-decorated GB-rich 2DLMs in the design of ultra-sensitive biosensing platforms for the detection of biological targets beyond RNA, bringing new opportunities for novel healthcare technologies.

Electrochemistry/Photoelectrochemistry-Based Immunosensing and Aptasensing of Carcinoembryonic Antigen

Recently, electrochemistry- and photoelectrochemistry-based biosensors have been regarded as powerful tools for trace monitoring of carcinoembryonic antigen (CEA) due to the fact of their intrinsic advantages (e.g., high sensitivity, excellent selectivity, small background, and low cost), which play an important role in early cancer screening and diagnosis and benefit people's increasing demands for medical and health services. Thus, this mini-review will introduce the current trends in electrochemical and photoelectrochemical biosensors for CEA assay and classify them into two main categories according to the interactions between target and biorecognition elements: immunosensors and aptasensors. Some recent illustrative examples are summarized for interested readers, accompanied by simple descriptions of the related signaling strategies, advanced materials, and detection modes. Finally, the development prospects and challenges of future electrochemical and photoelectrochemical biosensors are considered.

MOF@COF Heterostructure Hybrid for Dual-Mode Photoelectrochemical-Electrochemical HIV-1 DNA Sensing

We developed a novel metal-organic framework (MOF)@covalent-organic framework (COF) hybrid with a hierarchical nanostructure and excellent photoactivity, which further acted as the bifunctional platform of a dual-mode photoelectrochemical (PEC) and electrochemical (EC) biosensor for detecting HIV-1 DNA via immobilizing the HIV-1 DNA probe. First, the presynthesized Cu-MOF nanoellipsoids were used as the template for the in situ growth of the COF network, which was synthesized using copper-phthalocyanine tetra-amine (CoPc-TA) and 2,9-bis[p-(formyl)phenyl]-1,10-phenanthroline as building blocks through the Schiff base condensation. In view of the large specific surface area, abundant reserved amino group, excellent electrochemical activity, and high photoactivity, the obtained Cu-MOF@CuPc-TA-COF heterostructure not only can serve as the sensitive platform for anchoring the HIV-1 DNA probe strands but also can be utilized as the signal transducers for PEC and EC biosensors. Thereby, the constructed biosensor shows the sensitive and selective analysis ability toward the HIV-1 target DNA via the complementary hybridization between probe and target DNA strands. The dual-mode PEC and EC measurements revealed that the Cu-MOF@CuPc-TA-COF-based biosensor displayed a wide linear detection range from 1 fM to 1 nM and an extremely low limit of detection (LOD) of 0.07 and 0.18 fM, respectively. In addition, the dual-mode PEC-EC biosensor also demonstrated remarkable selectivity, high stability, good reproducibility, and preferable regeneration ability, as well as acceptable applicability, for which the detected HIV-1 DNA in human serum showed good consistency with real concentrations. Thereby, the present work can open a new dual-mode PEC-EC platform for detecting HIV-1 DNA based on the porous-organic framework heterostructure.

Recent applications of quantum dots in optical and electrochemical aptasensing detection of Lysozyme

Lysozyme (Lyz) is a naturally occurring enzyme that operates against Gram-positive bacteria and leads to cell death. This antimicrobial enzyme forms the part of the innate defense system of nearly all animals and exists in their somatic discharges such as milk, tears, saliva and urine. Increased Lyz level in serum is an important indication of several severe diseases and so, precise diagnosis of Lyz is an urgent need in biosensing assays. Up to know, various traditional and modern techniques have been introduced for Lyz determination. Although the traditional methods suffer from some significant limitations such as time-consuming, arduous, biochemical screening, bacterial colony isolation, selective enrichment and requiring sophisticated instrumentation or isotope labeling, some new modern approaches like aptamer-based biosensors (aptasensors) and quantum dot (QD) nanomaterials are the main goal in Lyz detection. Electrochemical and optical sensors have been highlighted because of their adaptability and capability to decrease the drawbacks of common methods. Using an aptamer-based biosensor, sensor selectivity is enhanced due to the specific recognition of the analyte. Thereby, in this review article, the recent advances and achievements in electrochemical and optical aptasensing detection of Lyz based on different QD nanomaterials and detection methods have been discussed in detail.

Nanostructure-based photoelectrochemical sensing platforms for biomedical applications

As a newly developed and powerful analytical method, the use of photoelectrochemical (PEC) biosensors opens up new opportunities to provide wide applications in the early diagnosis of diseases, environmental monitoring and food safety detection. The properties of diverse photoactive materials are one of the essential factors, which can greatly impact the PEC performance. The continuous development of nanotechnology has injected new vitality into the field of PEC biosensors. In many studies, much effort on PEC sensing with semiconductor materials is highlighted. Thus, we propose a systematic introduction to the recent progress in nanostructure-based PEC biosensors to exploit more promising materials and advanced PEC technologies. This review briefly evaluates the several advanced photoactive nanomaterials in the PEC field with an emphasis on the charge separation and transfer mechanism over the past few years. In addition, we introduce the application and research progress of PEC sensors from the perspective of basic principles, and give a brief overview of the main advances in the versatile sensing pattern of nanostructure-based PEC platforms. This last section covers the aspects of future prospects and challenges in the nanostructure-based PEC analysis field.

Visible light-activated self-powered photoelectrochemical aptasensor for ultrasensitive chloramphenicol detection based on DFT-proved Z-scheme Ag2CrO4/g-C3N4/graphene oxide

A visible light self-powered photoelectrochemical (PEC) aptasensor based on silver chromate particles, graphitic carbon nitride nanosheets and graphene oxide sheets (Ag₂CrO₄/g-C₃N₄/GO) for the ultrasensitive detection of chloramphenicol (CAP) was reported in this work. g-C₃N₄ was considered to be the fundamental photoelectric material because of its great oxidation ability of photogenerated hole as well as excellent biocompatibility and low toxicity. However, the narrow light absorption range and rapid carrier recombination rate limit the application of pure g-C₃N₄. Herein, Ag₂CrO₄ and GO as photosensitizer were introduced to improve the photoelectric properties of g-C₃N₄. The photocurrent of the developed ternary composite was about 3 times higher than that of pristine g-C₃N₄, which proves it can be used as a suitable photoelectric active material. Moreover, the mechanism of Z-scheme electron transfer path was proved by density functional theory (DFT) calculation. The fabricated PEC aptasensor exhibited high sensitivity toward CAP with a wide liner response of 0.5 pM to 50 nM and a detection limit of 0.29 pM. The specific recognition mechanism and excellent sensing performance indicated this aptasensor could serve as a useful tool for selective and ultrasensitive CAP detection in practical analysis.

A novel site-induced biomolecule anchoring strategy based on solid superacid ZrO2/SO42- for fabricating label-free IgG electrochemical immunosensors

In this work, a unique zirconium dioxide solid superacid (ZrO₂/SO₄²⁻) was utilized for the fabrication of an IgG electrochemical immunosensor.

Functional polymers in photoelectrochemical biosensing

Photoelectrochemical (PEC) analysis is a detection technique that has gained a wide attention in sensing applications. PEC presents the advantages of high sensitivity, low background signal, simple equipment and easy miniaturization. In PEC detection, light is used as an excitation source while current or voltage is measured as the output detection signal. The ability to couple the PEC process with specific bioreceptors gives PEC biosensing a unique advantage of being both selective and sensitive. The growing interest in PEC bioanalysis has resulted in essential progress in its analytical performance and biodetection applications. Functional polymers have different applications in the development of novel PEC biosensing platforms. Recently, the interest in polymer-based photoactive materials has emerged as they are efficient and less toxic alternatives to certain kinds of inorganic semiconductors and sensitizers. Moreover, molecularly imprinted polymers are a class of synthetic bioreceptors that are increasingly used in PEC bioanalytics. In this review, we will provide an overview on functional polymer-based PEC biosensing approaches. Novel classes of polymers as photoactive materials are reviewed and selected applications are described. Furthermore, molecularly imprinted polymers in the development of smart and sensitive PEC bioanalytical strategies are discussed.

Signal-on cathodic photoelectrochemical aptasensing of insulin: Plasmonic Au activated amorphous MoSx photocathode coupled with target-induced sensitization effect

Cathodic photoelectrochemical (PEC) bioassay is more resistant to reductive interferents, and development of high-performance photocathode is imperatively required in precise monitoring target in complex matrices. In this work, a plasmonic Au activated amorphous MoS_x photocathode (a-MoS_x/Au) was fabricated by sequential electrodeposition. Coupled with a sensitization amplification strategy induced by target-aptamer recognition, an ultrasensitive and high-affinitive signal-on cathodic PEC aptasensor for insulin detection was developed. Under optimum conditions, the sensor exhibits a wide linear range (0.1 pg/mL~100 ng/mL) and an ultralow detection limit (28 fg/mL) even lower than most sensors reported so far. Plasmonic Au activation and target-induced sensitization effect are responsible for high-performance PEC aptasensing of insulin at a-MoS_x photocathode.

Photonic Carbon Dots as an Emerging Nanoagent for Biomedical and Healthcare Applications

As a class of carbon-based nanomaterials, carbon dots (CDs) have attracted enormous attention because of their tunable optical and physicochemical properties, such as absorptivity and photoluminescence from ultraviolet to near-infrared, high photostability, biocompatibility, and aqueous dispersity. These characteristics make CDs a promising alternative photonic nanoagent to conventional fluorophores in disease diagnosis, treatment, and healthcare managements. This review describes the fundamental photophysical properties of CDs and highlights their recent applications to bioimaging, photomedicine (e.g., photodynamic/photothermal therapies), biosensors, and healthcare devices. We discuss current challenges and future prospects of photonic CDs to give an insight into developing vibrant fields of CD-based biomedicine and healthcare.

Superparamagnetic Nanostructures for Split-Type and Competitive-Mode Photoelectrochemical Aptasensing

Photoelectrochemical sensing has developed rapidly in the past decade because of its inherent advantages of economic devices and low background noise. However, traditional assembly of photoelectric beacons, probes, and targets on the ITO electrode solid-liquid interface inevitably leads to time-consuming, limited selectivity, poor stability, and nonreproducibility. To overcome these drawbacks, in this work, a unique split-type PEC aptasensor for carcinoembryonic antigen (CEA) was developed in virtue of the sandwich-like structure comprised of magnetic-optical Fe₃O₄@SiO₂@CdS-DNA₁, CEA aptamer, and signal element SiO₂-Au-DNA₂. The sandwich-like structure is easily formed in the liquid phase and can be triggered by competition from low-abundance CEA, resulting in dissociation. By further photocurrent measurement in pure phosphate buffer saline (PBS), coexisting species can be effectively removed from the modified electrode, improving selectivity, stability, and repeatability. These advantages benefit from the preparation of uniform and monodispersed Fe₃O₄@SiO₂@CdS and SiO₂-Au particles, DNAs assembly, and an elegant design. Additionally, the as-designed signal-on PEC aptasensor is highly sensitive, short time-consuming, and economical, enabling the detection of CEA in serum specimens. It not only provides an alternative to CEA immunosensors, but also paves the way for high-performance PEC aptasensors.

A differential photoelectrochemical method for glucose determination based on alkali-soaked zeolite imidazole framework-67 as both glucose oxidase and peroxidase mimics

A differential photoelectrochemical (PEC) method for glucose determination is reported using a nanocomposite with double mimic enzymes of glucose oxidase (GOx) and peroxidase. The nanocomposite was prepared by soaking zeolite imidazole framework-67 (ZIF-67) in 0.1 M NaOH solution at room temperature for 30 min, abbreviated as CoxOyHz@ZIF-67. The Michaelis-Menten constant of CoxOyHz@ZIF-67 to H2O2 and glucose is 121 μM and 3.95 mM, respectively. Using the photoelectrode of CoxOyHz@ZIF-67/TiO2 nanotubes (NTs), glucose was oxidized firstly by dissolved oxygen to generate H2O2 under the catalysis of CoxOyHz film as the mimics of GOx. The product of H2O2 enhanced the photocurrent of TiO2 NTs under the catalysis of ZIF-67 as the mimics of peroxidase. The molecular sieve effect of ZIF-67 frameworks reduces the interferences from molecules with size larger than the apertures in ZIF-67. Under the excitation of a 150 W xenon lamp with full spectrum, the photocurrent was measured in a two-electrode system without external additional potential. By using the photocurrent difference between two photocells, i.e CoxOyHz@ZIF-67/TiO2 NTs and Pt electrode, ZIF-67/TiO2 NTs and Pt electrode, as the signal, the selectivity for glucose determination is improved further. The differential PEC method was applied to the determination of glucose with a linear range 0.1 μM~1 mM and a detection limit of 0.03 μM. Graphical abstract.

Light-Addressable Electrodes for Dynamic and Flexible Addressing of Biological Systems and Electrochemical Reactions

In this review article, we are going to present an overview on possible applications of light-addressable electrodes (LAE) as actuator/manipulation devices besides classical electrode structures. For LAEs, the electrode material consists of a semiconductor. Illumination with a light source with the appropiate wavelength leads to the generation of electron-hole pairs which can be utilized for further photoelectrochemical reaction. Due to recent progress in light-projection technologies, highly dynamic and flexible illumination patterns can be generated, opening new possibilities for light-addressable electrodes. A short introduction on semiconductor–electrolyte interfaces with light stimulation is given together with electrode-design approaches. Towards applications, the stimulation of cells with different electrode materials and fabrication designs is explained, followed by analyte-manipulation strategies and spatially resolved photoelectrochemical deposition of different material types.

A self-powered photoelectrochemical cathodic aptasensor for the detection of 17β-estradiol based on FeOOH/In2S3 photoanode

In this work, a novel self-powered photoelectrochemical (PEC) aptasensor integrated photoanode and photocathode for the accurate and selective detection of 17β-estradiol (E₂) was proposed for the first time. FeOOH/In₂S₃ heterojunction was built initially and used as a substitute for platinum (Pt) counter electrode. The matched band gap edge of FeOOH and In₂S₃ facilitated the transfer of photo-generate electrons to photoanode, while the holes left in the valence band of photocathode (CuInS₂) can be attracted by the electrons flowed from the photoanode, which reduced the recombination of electron-hole pairs and promote the cathodic photocurrent. Under optimal conditions, the constructed cathodic aptasensor of E₂ presented linear scope in 10 fg/mL-1 μg/mL with detection limit of 3.65 fg/mL. Besides, the cathodic aptasensor exhibited admiring selectivity, stability and reproducibility. This work verified that the cathodic photocurrent response can be regulated by the corresponding photoanode which provided a new design thought for PEC aptasensor on the basis of p-type semiconductor.

Recent progress of heterostructure-based photoelectrodes in photoelectrochemical biosensing: a mini review

The heterostructure photoelectrodes have witted the rapid development to improve the performance of PEC biosensors recently.

Immobilization-free, split-mode cathodic photoelectrochemical strategy combined with cascaded amplification for versatile biosensing

We propose herein an immobilization-free, split-mode cathodic photoelectrochemical (PEC) strategy coupled with a cascaded amplification for versatile biosensing. Taking DNA and microRNA (miRNA) as the model targets, the hybridization between the targets and the hairpin probe triggers the digestion of the probe DNA by T7 exonuclease (T7 Exo), thus to generate G-quadruplex (G4) forming sequences, and then the released targets (DNA or miRNA) initiate the subsequent cycling processes and generate a large amount of G4 forming sequences. Subsequently, the formed G4 sequences associate with hemin to form the G4/hemin DNAzyme, which catalytically produces 1,4-bezoquinone (BQ) for conjugating onto the surface of the chitosan (CS) deposited BiOI/ITO photocathode via the quinone-chitosan conjugation chemistry (QCCC). Under photo excitation, the covalently attached quinones can act as electron acceptors of bismuth oxyiodine (BiOI), promoting the photocurrent generation and thus allowing the elegant and "signal-on" mode for probing targets of interest. Highly sensitive and selective PEC bioassays are readily realized, with the detection limits down to 2.2 fM (for DNA) and 0.2 fM (for miRNA). Since no labeling and no electrode modification processes are needed, this split-mode PEC biosensing strategy is amenable to convenient, time/labor saving, and high-throughput detections. More significantly, it provides a novel concept to design immobilization-free and label-free cathodic PEC biosensing systems, and showcases promise in general and versatile bioanalysis research.