Self-Powered Photoelectrochemical Aptasensor for Oxytetracycline Cathodic Detection Based on a Dual Z-Scheme WO3/g-C3N4/MnO2 Photoanode

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.

Photocurrent polarity switching photoelectrochemical aptasensor for oxytetracycline based on BiOBr/Ag2S/PDA//CuO: CuO-induced II-type to dual Z-scheme system

BACKGROUND

As a broad-spectrum tetracycline antibiotic, Oxytetracycline (OTC) was widely used in a variety of applications. But, the overuse of OTC had led to the detection of it in food, water and soil, which could present significance risk to human health and cause damage to ecosystem. It was of great significance to develop sensitive detection methods for OTC. Herein, an environmentally friendly photoelectrochemical (PEC) aptasensor was constructed for the sensitive detection of OTC based on CuO-induced BiOBr/Ag2S/PDA (Polydopamine) photocurrent polarity reversal.

RESULTS

BiOBr/Ag2S/PDA composites modified electrode not only produced stable initial anodic photocurrent but also provided attachment sites for the aptamer S1 of OTC by the strong adhesion of PDA. On the other hand, CuO loaded OTC aptamer S2 (Cu-S2) was got through Cu-S bonds. After the target OTC was identified on the electrode surface, CuO was introduced to the surface of ITO/BiOBr/Ag2S/PDA through the specific binding of OTC to S2. This identification process formed dual Z-type heterojunctions and resulted in a remarkable reversal of photocurrent polarity from anodic to cathodic. Under optimization conditions, the PEC aptasensor showed a wide linear range (50 fM ∼ 100 nM), low detection limit (1.9 fM), excellent selectivity, stability and reproducibility for the detection of OTC. Moreover, it was successfully used for the analysis of OTC in real samples of tap water, milk and honey, and had the potential for practical application.

SIGNIFICANCE

This work developed an environmentally friendly photocurrent-polarity-switching PEC aptasensor with excellent selectivity, reproducibility, stability, low LOD and wide linear range for OTC detection. This sensitive system, which was including BiOBr, Ag2S, PDA and CuO were low toxicity, not only reduced the risk of traditional toxic semiconductors to operators and the environment, but can also be used for the detection of real samples, broadening the wider range of applications for BiOBr, Ag2S, PDA and CuO.

A novel photoelectrochemical aptasensor based on 3D flower-like g-C3N4/BiOI p-n heterojunction for the sensitive detection of kanamycin

BACKGROUND

Kanamycin (KAN) residues in animal-derived foods continuously enter the human body, which will pose serious threats to human health such as hearing loss, nephrotoxicity and other complications. Therefore, to sensitively detect KAN residues by a reliable technology is extremely urgent in food quality and safety. Compared with traditional methods being limited by cost and complexity, photoelectrochemical (PEC) biosensors benefit from some merits such as rapid response, excellent sensitivity and good stability. In this study, the construction of a highly efficient PEC platform to realize KAN residues detection is discussed.

RESULTS

Herein, a novel p-n heterojunction consisting of flower-like BiOI microspheres and graphite carbon nitride (g-C3N4) nanoflakes was developed to establish a PEC aptasensor for KAN detection at 0 V. The prepared g-C3N4/BiOI heterostructure showed not only significantly enhanced PEC activity due to the larger specific surface area but also greatly increased charge separation efficiency owing to the strong internal electric field. Meanwhile, using g-C3N4/BiOI as a highly efficient photoactive material for binding amine-functionalized aptamers to capture KAN, the photocurrent signals showed a 'turn off' mode to achieve the sensitive detection of KAN. The proposed PEC aptasensor exhibited linear response for KAN from 5 × 10-9 to 3 × 10-7 mol L-1 with a low detection limit of 1.31 × 10-9 mol L-1, and satisfactory recoveries (97.44-107.38 %) were obtained in real food samples analysis.

SIGNIFICANCE

This work presented a novel p-n heterojunction-based PEC aptasensor with strong selectivity and stability, rendering it allowed to detect KAN in animal-derived foods including milk, honey and pork. Additionally, the detection range satisfied the MRLs for KAN specified by the national standards, demonstrating the potential application for food analysis. The study provides a new insight into the development of efficient and practical biosensors for antibiotic residues detection.

A novel dual-model photoelectrochemical/electrochemical sensor based on Z-scheme TiO2 disks/methylene blue for kanamycin detection

Herein, a new dual-model photoelectrochemical (PEC)/electrochemical (EC) sensor based on Z-scheme titanium dioxide (TiO2) disk/methylene blue (MB) sensibilization for the detection of kanamycin (Kana) was developed. Metal-organic framework-derived porous TiO2 disks were synthesized and exhibited excellent anodic photocurrent under visible light excitation. Subsequently, amino-labeled double-stranded DNA (dsDNA) was introduced into the modified electrode. Photocurrent was enhanced with MB embedded in dsDNA to form Z-scheme TiO2/MB sensibilization. When the target, Kana, was present, it specifically bound to the aptamer in the dsDNA, leading to the disruption of the dsDNA structure and the release of MB. This release of MB and the increase in target spatial resistance resulted in a significant weakening of PEC signal and a decreased oxidation peak current of MB. The PEC sensor successfully detected Kana in the range of 2-1000 pM with an LOD of 0.17 pM. Meanwhile, the EC sensor for Kana detection showed a linear range of 5-500 pM with an LOD of 1.8 pM. Additionally, the sensor exhibited excellent selectivity, reproducibility, stability, and good recoveries when applied to milk and honey samples. As a result, this method has the potential for application in ensuring food safety through the rapid determination of antibiotics in food.

MOF-derived sandwich-structured dual Z-Scheme Co9S8@ZnIn2S4/CdSe hollow nanocages heterojunction: Target-induced ultrasensitive photoelectrochemical sensing of chlorpyrifos

Exploring efficient photoactive material presents an intriguing opportunity to enhance the analytical performance of photoelectrochemical (PEC) sensor in the environmental analysis. In this work, a sandwich-structured multi-interface Co9S8@ZnIn2S4/CdSe QDs dual Z-Scheme heterojunction, derived from metal-organic framework (MOF), was synthesized as a sensing platform for chlorpyrifos detection, by integrating with enzyme-induced in situ insoluble precipitates strategy. The meticulously designed Co9S8@ZnIn2S4/CdSe QDs exhibited enhanced charge separation efficiency and was proved to be a highly effective sensing platform for the immobilization of biomolecules, attributing to the intrinsic dual Z-Scheme heterojunction and the distinctive hollow structure. The proposed PEC sensing platform combined with enzyme-induced in situ precipitate signal amplification strategy achieved superior performance for sensing of chlorpyrifos (CPF), showing in wide linear range (1.0 pg mL-1-100 ng mL-1), with a limit of detection (0.6 pg mL-1), excellent selectivity, and stability. This work offers valuable insights for the design of novel advanced photoactive materials aimed at detecting environmental pollutants with low level concentration.

Self-powered photoelectrochemical immunosensing platform for sensitive CEA detection using dual-photoelectrode synergistic signal amplification

Self-powered photoelectrochemical (PEC) sensing, as an emerging sensing mode, can effectively solve the problems such as weak anti-interference ability and poor signal response of individual photoanode or photocathode sensing. In this work, an ITO/Co-CuInS2 photocathode and ITO/WO3@CdS photoanode based self-powered cathodic PEC immunosensor was developed, which integrated dual-photoelectrode to synergistic amplify the signal for highly sensitive and specific detection of carcinoembryonic antigen (CEA). The self-powered PEC sensor could drive electrons transfer through the difference in Fermi levels between the two photoelectrodes without an external bias voltage. The photoanode was introduced to amplify the photoelectric signal, and the photocathode was only designed for the construction of sensing interfaces. The proposed sensor quantitatively determined the target CEA with the detection limit of 0.23 pg/mL and a linear correlation confine of 0.1 pg/mL ∼100 ng/mL. The constructed immunosensing platform exhibited high sensitivity, satisfactory stability and great biological detection selectivity, providing a feasible and effective strategy for the manufacture of new self-powered sensors in high-performance PEC bioanalytical applications.

Recent Trends in Self-Powered Photoelectrochemical Sensors: From the Perspective of Signal Output

Revolutionary developments in analytical chemistry have led to the rapid development of self-powered photoelectrochemical (PEC) sensors. Different from conventional PEC sensors, self-powered PEC sensors do not require an external power source or complex devices for the sensitive detection of targets. As a result, these sensors have enormous application potential for the development of novel portable sensors. An increasing body of work is making excellent progress toward the implementation of self-powered PEC sensors for detection, but there have been no reviews to date. The present review first introduces the state of the art in the development of self-powered PEC sensors. Then, different types of self-powered PEC sensors are summarized and discussed in detail, including their current, power, and potential. Additionally, single- and dual-photoelectrode systems are classified and systematically compared. Finally, the current developments and major challenges that need to be addressed are also summarized. This review provides valuable insights into the current state of self-powered PEC sensors to promote further progress in this field.

Z-Scheme Heterojunction Excited by DNA-Programmed Upconversion Nanotransducers for a Near-Infrared Light-Actuated Lab-on-Paper Device

Herein, a flexible near-infrared (NIR) light-actuated photoelectrochemical (PEC) lab-on-paper device was constructed toward miRNA-122 detection, utilizing the combination of DNA-programmed NaYF4/Yb,Tm upconversion nanoparticles (UCNPs) and the Z-scheme AgI/WO3 heterojunction grown in situ on gold nanoparticle-decorated 3D cellulose fibers. The UCNPs were employed as light transducers for converting NIR light into ultraviolet/visible (UV/vis) light to excite the nanojunction. The multiple diffraction of NaYF4/Yb,Tm matched the absorption band of the Z-scheme AgI/WO3 heterojunction, resulting in enhanced PEC photocurrent output. This prepared Z-scheme heterojunction effectively directed charge migration and highly facilitated the electron-hole pair separation. Target miRNA-122 activated the nonenzyme catalytic hairpin assembly signal amplification strategy, generating duplexes which caused the exfoliation of NaYF4/Yb,Tm UCNPs from the biosensor electrode and lowered the photocurrent under 980 nm irradiation. Under optimized circumstances, the proposed NIR-actuated PEC lab-on-paper device presented accurate miRNA-122 detection within a wide linear range of 10 fM-100 nM with a low limit of detection of 2.32 fM, providing a reliable strategy in the exploration of NIR-actuated PEC biosensors for low-cost, high-performance bioassay in clinical applications.

HOF-101-based dual-mode biosensor for photoelectrochemical/electrochemiluminescence detection and imaging of oxytetracycline

A unique hydrogen-bonded organic frameworks (HOF-101)-based photoelectrochemical (PEC) and electrochemiluminescence (ECL) dual-mode biosensor using polydopamine nanoparticles (PDAs) as quencher was constructed for ultrasensitive detection and imaging of oxytetracycline (OXY). In particular, HOF-101 was a superior ECL material and can be observed with the naked eye. Furthermore, it also had outstanding PEC signal, so HOF-101 was a new dual-signal material with excellent performance, thus it was explored to realize dual-mode detection. As the main component of natural melanin, PDAs not only had good biocompatibility, but also contained rich functional groups on the surface. Additionally, PDAs had excellent light absorption ability and poor conductivity, which made it the excellent photoquencher. In this work, PDAs were introduced on the surface of HOF-101 to quench its ECL and PEC signals by using the dual-aptamer sandwich method, achieving ultrasensitive detection of antibiotic OXY. Particularly for ECL detection, HOF-101 was firstly used to visually detect OXY. The detection range can reach 0.1 pM-100 nM, and the limit of detection (LOD) can reach 0.04 pM. This work showed a great contribution to the development of new ECL-PEC materials and ECL visualization analysis, which had outstanding application potential in the fields of food safety and biochemical analysis.

A self-powered photoelectrochemical biosensing platform for H-FABP monitoring mediated by CsPbBr3@COF-V

Advanced bioelectronic detection based on the integration of modern optical electronics and biological systems has a broad prospect. The strategy of cathode signal amplification in self-powered photoelectrochemical (PEC) immunosensors with excellent performance is rarely reported in the field of immune analysis. Herein, the work demonstrates a self-powered PEC biosensor formed with BiOI photocathode and WO3/SnS2/ZnS photoanode, and CsPbBr3@COF-V was used as the photocathode signal quenching source for the quantitative monitoring of heart fatty acid binding protein (H-FABP). The high efficiency and stable self-powered biosensor formed not only provides continuous and powerful photocurrent response for bioanalysis through reasonable stepped band structure, but also effectively eliminates the interference of reducing substances. The quenching source CsPbBr3@COF-V greatly affects the photocurrent response due to steric hindrance, weak conductivity, competition with the substrate for dissolved oxygen and excitation light source. And the intervention of this key factor achieves multiple signal amplification effect and opens up an innovative vision for self-powered PEC immunosensor. Taking H-FABP as a representative analyte, the proposed signal amplification self-powered photoelectrochemical presents a broad linear range from 0.0005 to 150 ng/mL with the detection limit of 0.19 pg/mL.

Photoelectrochemical aptasensing of lincomycin based on a AgI-carboxylated multiwalled carbon nanotubes-BiOI Z-scheme heterojunction

Lincomycin (LIN) is a common antibiotic that is widely used in animal husbandry and other fields, and the residual problem caused by its abuse has attracted widespread attention. Herein, a novel AgI-carboxylated multiwalled carbon nanotubes (cMWCNT)-BiOI Z-scheme heterojunction material was synthesized via a one-pot hydrothermal method, modified on a fluorine-doped tin oxide (FTO) electrode surface, and used for detecting LIN. The photocurrent on the AgI-cMWCNT-BiOI/FTO photoelectrode is 4.6 times that on the control AgI-BiOI/FTO photoelectrode. An amino-functionalized LIN aptamer was fixed on the AgI-cMWCNT-BiOI/FTO photoelectrode by the cross-linking reaction between chitosan and glutaraldehyde, and then Ru(NH3)63+ was electrostatically attached to the LIN aptamer to increase the photocurrent response to the LIN binding. When LIN binds competitively with Ru(NH3)63+ to the aptamer, the photocurrent signal can be quantitatively decreased. Under optimized conditions, the anodic photocurrent at 0 V vs KCl-saturated calomel electrode in 0.1 M phosphate buffer (pH 7.0) containing 0.100 M ascorbic acid was linear with the common logarithm of LIN concentration from 10.0 pM to 500 nM, with a limit of detection of 2.8 pM (S/N = 3). Satisfactory recovery results were obtained in the analysis of cow milk samples.

Self-powered photoelectrochemical/visual sensing platform based on PEDOT/BiOBr0.8I0.2 organic-inorganic hybrid material and MWCNTs/SnS2 heterojunction for the ultrasensitive detection of programmed death ligand-1

Programmed death ligand-1 (PD-L1) can enhance the immune tolerance of tumor cells by suppressing the activity of T-cells, and is one of the culprits that lead to the immune escape of tumor cells. Thus, the sensitive and portable detection of PD-L1 levels is essential for many types of tumor prognosis. Herein, a novel dual-mode analytical device for the ultrasensitive detection of PD-L1 has been developed. In this configuration, an advanced organic-inorganic hybrid material of poly(3,4-ethylenedioxythiophene) -BiOBr0.8I0.2 is designed as photocathode to enhance the photogenerated electron migration efficiency of the MWCNTs/SnS2-photoanode by external circuit, amplifying cathodic photocurrent without extra energy supply. The PD-L1 aptamer is loaded on the photocathode surface to ensure selectivity. The obtained sensing platform can achieve highly sensitive and specific detection of PD-L1 in complex environment, with a low detection limit of 0.29 pg mL-1. On the other hand, electrochromic material Prussian blue (PB) and MWCNTs/SnS2 are integrated to fabricate a portable sensing chip for PD-L1. Under illumination, photogenerated electrons of MWCNTs/SnS2 are injected into Prussian blue, and the blue PB is reduced to white product, indicating the concentration of PD-L1, without need of other instrument. This self-powered photoelectrochemical and visual analysis system has good practicability and is a promising clinical diagnosis tool.

A ZnIn2S4/Ag2CO3 Z-scheme heterostructure-based photoelectrochemical biosensor for neuron-specific enolase

An efficient photo-to-electrical signal is pivotal to photoelectrochemical (PEC) biosensors. In our work, a novel PEC biosensor was fabricated for the detection of neuron-specific enolase (NSE) based on a ZnIn2S4/Ag2CO3 Z-scheme heterostructure. Due to the overlapping band potentials of the ZnIn2S4 and Ag2CO3, the formed Z-scheme heterostructure can promote the charge separation and photoelectric conversion efficiency. And the concomitant Ag nanoparticles in Ag2CO3 provided multiple functions to enhance the PEC response of the Z-scheme heterostructure. It acts not only as a bridge for the transfer of carriers between ZnIn2S4 and Ag2CO3, promoting the constructed Z-scheme heterostructure, but also as electron mediators to accelerate the transfer of photogenerated carriers and improve the capture of visible light of the Z-scheme heterostructure by surface plasmon resonance (SPR). Compared with single Ag2CO3 and ZnIn2S4, the photocurrent of the designed Z-scheme heterostructure increased more than 20 and 60 times respectively. The fabricated PEC biosensor based on a ZnIn2S4/Ag2CO3 Z-scheme heterostructure exhibits sensitive detection to NSE, and presents a linear range of 50 fg·mL-1 ~ 200 ng·mL-1 with a limit of detection of 4.86 fg·mL-1. The proposed PEC biosensor provides a potential approach for clinical diagnosis.

Photo-assisted Zn-air battery-driven self-powered aptasensor based on the 2D/2D Schottky heterojunction of cadmium-doped molybdenum disulfide and Ti3C2Tx nanosheets for the sensitive detection of penicillin G

A novel photocatalyzed Zn-air battery-driven (ZAB)-based aptasensor has been manufactured using the two dimensional (2D)/2D Schottky heterojunction as photocathode and Zn plate as photoanode. It was then employed to sensitively and selectively detect penicillin G (PG) in the complex environment. The 2D/2D Schottky heterojunction was established by the in situ growth of cadmium-doped molybdenum disulfide nanosheets (Cd-MoS₂ NSs) around Ti₃C₂T_x NSs (denoted as Cd-MoS₂@Ti₃C₂T_x) by using phosphomolybdic acid (PMo₁₂) as precursor, thioacetamide as sulfur source, and Cd(NO₃)₂ as a doping agent through the hydrothermal method. The gained Cd-MoS₂@Ti₃C₂T_x heterojunction possessed contact interface, hierarchical structure, and plenty of sulfur and oxygen vacancies, thus showing the enhanced separation ability of photocarriers and electron transfer. Due to the enhanced UV-vis light adsorption ability, high photoelectric conversion efficiency, and exposed catalytic active sites, the constructed photocatalyzed ZAB displayed a boosted output voltage of 1.43 V under UV-vis light irradiation. The developed ZAB-driven self-powered aptasensor demonstrated an ultralow detection limit of 0.06 fg mL^-1 within a PG concentration ranged from 1.0 fg mL^-1 to 0.1 ng mL^-1, as deduced from the power density-current curves, along with high specificity, good stability and promising reproducibility, as well as excellent regeneration ability and wide applicability. The present work provided an alternative analysis method for the sensitive analysis of antibiotics based on the portable photocatalyzed ZAB-driven self-powered aptasensor.

Biological redox cycling amplification in a self-powered photoelectrochemical sensor based on TiO2/CdIn2S4/ g-C3N4-WO3 photoanode for sensitive detection of Hg2

A photoelectrochemical (PEC) sensor is proposed with a TiO₂/CdIn₂S₄ co-sensitive structure and a g-C₃N₄-WO₃ heterojunction as the photoanode to form a self-powered system. The photogenerated hole-induced biological redox cycle of TiO₂/CdIn₂S₄/g-C₃N₄-WO₃ composites is used as a signal amplification strategy for Hg²⁺ detection. In the test solution, ascorbic acid is first oxidized by the photogenerated hole of the TiO₂/CdIn₂S₄/g-C₃N₄-WO₃ photoanode, which triggers the ascorbic acid－glutathione cycle to achieve signal amplification and increase the photocurrent. However, in the presence of Hg²⁺, glutathione forms a complex with Hg²⁺, which destroys the biological cycle and leads to a decreased of photocurrent, thus achieving detection of Hg²⁺. Under optimal conditions, the proposed PEC sensor has a wider range (from 0.1 pM to 100 nM), and lower limit of Hg²⁺ detection (0.44 fM) than most other Hg²⁺ detection methods. In addition, the developed PEC sensor can be used to detect of real samples.

Facile synthesis of NiAl2O4/g-C3N4 composite for efficient photocatalytic degradation of tetracycline

Designing high-efficiency photocatalysts responsive to visible light is important for the degradation of antibiotics in water. Heterojunction engineering is undoubtedly an effective strategy to improve the photocatalytic performance. In this work, spinel-type metal oxides (NiAl₂O₄, NAO) are synthesized by a simple sol-gel and calcination process. After compounding graphitic carbon nitride (g-C₃N₄), NAO/g-C₃N₄ heterojunction is obtained, which then is used as the photocatalyst for tetracycline hydrochloride (TC). The effects of photocatalyst dosage, the initial concentration of TC, and solution pH on photodegradation performance are systematically studied. The removal rate of TC on NAO/g-C₃N₄ reach up to ∼90% after visible light irradiation for 2 hr and the degradation rate constant is ∼7 times, and ∼32 times higher than that of pure NAO and g-C₃N₄. The significantly improved photocatalytic activity can be attributed to the synergistic effect between well matched energy levels in NAO/g-C₃N₄ heterojunctions, improvement of interfacial charge transfer, and enhancement of visible light absorption. This study provides a way for the synthesis of efficient photocatalysts and an economic strategy for removing antibiotics contamination in water.

Photoelectrochemical aptasensing of oxytetracycline based on a BiVO4-carboxylated graphene-WO3 Z-scheme heterojunction

A new BiVO₄-carboxylated graphene (cG)-WO₃ Z-scheme heterojunction was constructed on a fluorine-doped tin oxide (FTO) substrate electrode by ultrasonic mixing and cast-coating for determination of oxytetracycline (OTC). Since cG can absorb visible light and well match with the energy levels of WO₃ and BiVO₄ to promote the charge separation and transfer, the photocurrent on the BiVO₄-cG-WO₃/FTO photoelectrode is 4.4 times that on the control BiVO₄-WO₃/FTO photoelectrode. An amino-functionalized OTC aptamer was fixed on the BiVO₄-cG-WO₃/FTO photoelectrode by the 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide mediated amide reaction, and then hexaammonium ruthenium(III) (Ru(NH₃)₆³⁺) was attached to the OTC aptamer to increase the photocurrent response to the OTC binding. Under the optimized conditions, the photocurrent on the BiVO₄-cG-WO₃/FTO photoelectrode at 0 V vs SCE was linear with the common logarithm of OTC concentration from 0.01 nM to 500 nM, with a limit of detection of 3.1 pM (S/N = 3). Satisfactory recovery results were obtained in the analysis of real water samples.

Advancements in nanomaterial-based aptasensors for the detection of emerging organic pollutants in environmental and biological samples

The combination of nanomaterials (NMs) and aptamers into aptasensors enables highly specific and sensitive detection of diverse pollutants. The great potential of aptasensors is recognized for the detection of diverse emerging organic pollutants (EOPs) in different environmental and biological matrices. In addition to high sensitivity and selectivity, NM-based aptasensors have many other advantages such as portability, miniaturization, facile use, and affordability. This work showcases the recent advances achieved in the design and fabrication of NM-based aptasensors for monitoring EOPs (e.g., hormones, phenolic contaminants, pesticides, and pharmaceuticals). On the basis of their sensing mechanisms, the covered aptasensing systems are classified as electrochemical, colorimetric, PEC, fluorescence, SERS, and ECL. Special attention has been paid to the fabrication processes, analytical achievements, and sensing mechanisms of NM-based aptasensors. Further, the practical utility of aptasensing approaches has also been assessed based on their basic performance metrics (e.g., detection limits, sensing ranges, and response times).

Dual-response fluorescent probe based on nitrogen-doped carbon dots and europium ions hybrid for ratiometric and on-site visual determination of oxytetracycline and tetracycline

Tetracyclines residues, particularly oxytetracycline (OTC) and tetracycline (TC), have raised extensive concern because of their serious adverse effects on human health. Herein, a dual-response fluorescent probe based on nitrogen-doped carbon dots (N-CDs) and Eu³⁺ hybrid (N-CDs-Eu³⁺) was developed to selectively determine OTC and TC. The N-CDs act as ancillary ligands of Eu³⁺ and recognition units of OTC/TC, while the Eu³⁺ ions chelated with N-CDs can also specifically recognize OTC/TC. Upon inclusion of OTC/TC, an enhancement in Eu³⁺ emission occurs due to the energy transfer from OTC/TC to Eu³⁺ and the efficient elimination of quenching effect caused by H₂O molecule, which is attributed to the incorporation of N-CDs; while the blue fluorescence emitted by the N-CDs decreases under the inner filter effect and static quenching effect caused by OTC/TC. Based on the double and reverse response signals, the ratiometric detection of OTC and TC in the range of 0.1-45 μΜ and 0.1-30 μΜ is achieved with a detection limit of 0.017 and 0.041 μM, respectively. In addition, the noticeable variation in fluorescence color of the probe is integrated with a smartphone-assisted analysis device for the rapid on-site quantitative assay of OTC, where the detection limit is 0.15 μΜ. The results show that this probe performs with excellent specificity and anti-interference for both OTC and TC, and satisfactory detection results are obtained in lake water, milk, and honey samples, thereby confirming that the probe exhibits promising application in food safety and environmental monitoring.

Fast, specific, and ultrasensitive antibiotic residue detection by monolayer WS2-based field-effect transistor sensor

Antibiotic residues cause increasing concern in environmental ecology and public health, which needs efficient analysis strategy for monitoring and control. In this study, a fast, specific, and ultrasensitive sensor based on field-effect transistor (FET) has been proposed for the detection of ampicillin (AMP). The sensor involves monolayer tungsten disulfide (WS₂) nanosheet as the sensing channel, single-stranded DNA (ssDNA) as the sensing probe, and gold nanoparticle (Au NP) as the linker. The WS₂/Au/ssDNA FET sensor responds rapidly to AMP in a wide linear detection range (10^-12-10^-6 M) and has low limit of detection (0.556 pM), which meets the permissible standards of AMP in water and food. The sensing mechanism study suggests that the excellent sensor response results from the increased number of negative charges in the Debye length and the consequent accumulation of holes in WS₂ channel after the addition of AMP. Moreover, satisfactory sensing performance was confirmed in real water samples, indicating the potential application of the proposed method in practical AMP detection. The reported FET sensing strategy provides new insights in antibiotic analysis for risk assessment and control.

Dual Direct Z-Scheme Heterojunction with Stable Electron Supply to a Au/PANI Photocathode for Ultrasensitive Photoelectrochemical and Electrochromic Visualization Detection of Ofloxacin in a Microfluidic Sensing Platform

A novel dual-mode microfluidic analytical device integrating self-powered photoelectrochemical (PEC) sensing with electrochromic visualization analysis was developed for ultrasensitive ofloxacin (OFL) detection. First, an advanced dual direct Z-scheme BiVO₄@Ni-ZnIn₂S₄/Bi₂S₃ (BVZIS) heterojunction was designed as a photoanode matrix to steadily provide electrons. The dual Z-scheme structure formed in photoactive BVZIS composites greatly accelerated the migration of electrons. In addition, the doping of Ni in ZnIn₂S₄ markedly enhanced the optical absorption and promoted the separation of the photocarrier. Second, electrochromic material polyaniline-modified Au (Au/PANI) was first electrodeposited on the photocathode for immobilizing aptamers and realizing visualized readout. On the one hand, Au/PANI with excellent conductivity could receive electrons from the photoanode without external energy supply. On the other hand, PANI would be rapidly reduced by the received electrons and change its color from blue to green obviously. With the increase in OFL, the increased steric hindrance resulted in the significant decline in the PEC signal and RGBgreen value. Third, wide linear ranges of PEC (0.05 pg/mL to 150 ng/mL) and electrochromic technique (0.1 pg/mL to 100 ng/mL) as well as low detection limits of PEC (18 fg/mL) and electrochromic (30 fg/mL) sensors could achieve the ultrasensitive detection of OFL in milk and river water.

PEC/Colorimetric Dual-Mode Lab-on-Paper Device via BiVO4/FeOOH Nanocomposite In Situ Modification on Paper Fibers for Sensitive CEA Detection

A dual-mode lab-on-paper device based on BiVO₄/FeOOH nanocomposites as an efficient generating photoelectrochemical (PEC)/colorimetric signal reporter has been successfully constructed by integration of the lab-on-paper sensing platform and PEC/colorimetric detection technologies for sensitive detection of carcinoembryonic antigen (CEA). Concretely, the BiVO₄/FeOOH nanocomposites were in situ synthesized onto the paper-working electrode (PWE) through hydrothermal synthesis of the BiVO₄ layer on cellulose fibers (paper-based BiVO₄) which were initially modified by Au nanoparticles for improving the conductivity of three dimensional PWE, and then the photo-electrodeposition of FeOOH onto the paper-based BiVO₄ to construct the paper-based BiVO₄/FeOOH for the portable dual-mode lab-on-paper device. The obtained nanocomposites with an FeOOH needle-like structure deposited on the BiVO₄ layer exhibits enhanced PEC response activity due to its effective separation of the electron-hole pair which could further accelerate the PEC conversion efficiency during the sensing process. With the introduction of CEA targets onto the surface of nanocomposite-modified PWE assisted by the interaction with the CEA antibody from a specific recognition property, a signal-off PEC signal state with a remarkable photocurrent response decreasing trend can be achieved, realizing the quantitative detection of CEA with the PEC signal readout mode. By means of a smart origami paper folding, the colorimetric signal readout is achieved by catalyzing 3,3',5,5'-tetramethylbenzidine (TMB) to generate blue oxidized TMB in the presence of H₂O₂ due to the satisfied enzyme-like catalytic activity of the needle-like structure, FeOOH, thereby achieving the dual-mode signal readout system for the proposed lab-on-paper device. Under the optimal conditions, the PEC and colorimetric signals measurement were effectively carried out, and the corresponding linear ranges were 0.001-200 ng·mL^-1 and 0.5-100 ng·mL^-1 separately, with the limit of detection of 0.0008 and 0.013 ng·mL^-1 for each dual-mode. The prepared lab-on-paper device also presented a successful application in serum samples for the detection of CEA, providing a potential pathway for the sensitive detection of target biomarkers in clinical application.

Dual fluorescent aptasensor for simultanous and quantitative detection of sulfadimethoxine and oxytetracycin residues in animal-derived foods tissues based on mesoporous silica

Herein, we developed a dual fluorescent aptasensor based on mesoporous silica to simultaneously detect sulfadimethoxine (SDM) and oxytetracycline (OTC) in animal-derived foods. We immobilized two types of aptamers modified with FAM and CY5 on the silica surface by base complementary pairing reaction with the cDNA modified with a carboxyl group and finally formed the aptasensor detection platform. Under optimal conditions, the detection range of the aptasensor for SDM and OTC was 3-150 ng/mL (R ² = 0.9831) and 5-220 ng/mL (R ² = 0.9884), respectively. The limits of detection for SDM and OTC were 2.2 and 1.23 ng/mL, respectively. The limits of quantification for SDM and OTC were 7.3 and 4.1 ng/mL, respectively. Additionally, the aptasensor was used to analyze spiked samples. The average recovery rates ranged from 91.75 to 114.65% for SDM and 89.66 to 108.94% for OTC, and all coefficients of variation were below 15%. Finally, the performance and practicability of our aptasensor were confirmed by HPLC, demonstrating good consistency. In summary, this study was the first to use the mesoporous silica-mediated fluorescence aptasensor for simultaneous detection of SDM and OTC, offering a new possibility to analyze other antibiotics, biotoxins, and biomolecules.

Ion-Exchange Reaction-Mediated Hierarchical Dual Z-Scheme Heterojunction for Split-Type Photoelectrochemical Immunoassays

Photoelectrochemical (PEC) immunoassays with ultrasensitive detection abilities are highly desirable for in vitro PEC diagnosis and biological detection. In this paper, dual Z-scheme PEC immunoassays with hierarchical nanostructures (TiO₂@NH₂-MIL-125@CdS) are synthesized through epitaxial growth of MOF-on-MOF and further in situ derivatization. The dual Z-scheme configuration not only extends the light absorption range but also increases the redox ability due to the interface structure nanoengineering, which synergistically suppresses bulk carrier recombination and promotes the charge transfer efficiency at the electron level. Furthermore, a smart MOF-derived labeling probe (CuO@ZnO nanocube) is designed to develop a split-type PEC biosensor by using prostate-specific antigen (PSA) as a target biomarker. In the presence of PSA, the Ab₂-labeled CuO@ZnO would specifically bond to the dual Z-scheme electrode. Then, the MOF-derived CuO@ZnO is dissolved by hydrochloric acid to release Cu²⁺, which could replace Cd²⁺ via an ion-exchange reaction, thus leading to the decrease of the photocurrent due to the destruction of the dual Z-scheme configuration. In typical applications, the split-type PEC immunoassay exhibits an excellent detection performance for PSA with a LOD as low as 0.025 pg·mL^-1.

Construction and excellent photoelectric synergistic anticorrosion performance of Z-scheme carbon nitride/tungsten oxide heterojunctions

The use of heterojunctions for metal corrosion protection is a highly innovative and challenging task. Based on the composition and structure of tungsten oxide-based heterojunctions, Z-scheme heterojunctions were designed and synthesized by the electrostatic self-assembly method using energy band-matched g-C₃N₄ and WO₃ materials. Applied in the field of anticorrosion, they overcame the problems of poor reduction ability and transmission inefficiency of traditional materials. The Z-scheme heterojunctions ensured unidirectional electron transfer, while the aggregation of the retained strongly reduced electrons on the surface of the iron substrates provided a strong driving force for retarding corrosion occurrence. Meanwhile, the inherent shielding properties of the two-dimensional material g-C₃N₄ and the confinement of chloride ions as an electroactive layer hindered the penetration of the corrosive solution. After being corroded for 72 h, the corrosion impedance of the g-C₃N₄/WO₃ heterojunction system was improved by 640.11% compared with the epoxy resin coating. In addition, the g-C₃N₄/W₁₈O₄₉ heterojunction was synthesized by using mixed valence tungsten oxide, which overcame the problems of photogenerated electron yield and lifetime, and enhanced the anticorrosion performance compared with a single g-C₃N₄ phase. This research provided ideas for designing efficient and environmentally friendly heterojunction anticorrosion materials.

Catalytic Decomposition of the Hole-Derived H2O2 by AgBiS2@Ag Nanozyme to Enhance the Photocurrent of Z-Scheme BiVO4/ZnIn2S4 Photoelectrode in Microfluidic Immunosensing Platform

A novel microfluidic photoelectrochemical (PEC) analytical device based on AgBiS₂@Ag nanozyme-mediated signal amplification was developed for ultrasensitive detection of cytokeratin 19 fragment 21-1 (CYFRA 21-1). First, a brand new Z-scheme BiVO₄/ZnIn₂S₄ (BZIS) photoactive material was utilized as a sensing matrix to supply a stable photocurrent. Under anodic bias, the photoexcited holes in BiVO₄ could oxidize water to produce hydrogen peroxide (H₂O₂), which markedly enhanced the separation efficiency of the electron-hole pairs. Besides, the Z-scheme heterojunction formed between BiVO₄ and ZnIn₂S₄ further accelerated the transport of the electron. Second, for improving the sensitivity of the PEC sensor, a new strategy of catalytic dissociation of the hole-derived H₂O₂ by AgBiS₂@Ag nanozyme was proposed to amplify the PEC signal. AgBiS₂@Ag composites, possessing an excellent peroxidase-mimicking feature, could efficiently catalyze the H₂O₂ to produce hydroxyl radicals (^•OH) and lead to the significant enhancement of the photocurrent. Third, automatic sample injection and detection were successfully realized by integrating the photoelectrode into microfluidic chips. Based on this advanced sensing strategy, the designed microfluidic PEC sensor displayed a wide linear range (0.1 pg/mL - 100 ng/mL) and a low detection limit of 35 fg/mL (S/N = 3), which could be efficiently applied to the ultrasensitive determination of CYFRA 21-1 in a human serum sample.

A Direct Z-Scheme AgBr/CuBi2O4 Photocathode for Ultrasensitive Detection of Ciprofloxacin and Ofloxacin by Controlling the Release of Luminol in Self-Powered Microfluidic Photoelectrochemical Aptasensors

An innovative self-powered microfluidic photoelectrochemical (PEC) aptasensor was developed that uses photoactive AgBr/CuBi₂O₄ (ACO) composites as the photocathode matrix for ultrasensitive detection of ciprofloxacin (CIP) and ofloxacin (OFL). The formation of direct Z-scheme heterojunctions in ACO composites greatly aided electron/hole pair separation. Meanwhile, ZnIn₂S₄-decorated CdS nanorod arrays (CZIS) as the photoanode were used instead of a platinum counter electrode to provide electrons. The "signal-off" CIP detection was accomplished through the steric hindrance effect in the photoanode due to the combination of aptamer_(CIP) and CIP. To increase the cathodic photocurrent intensity for OFL determination, controlled release of luminol was first used. Luminol molecules were successfully embedded in the porous structure of silicon dioxide nanospheres (PSiO₂) by the electrostatic adsorption between PSiO₂ and aptamer_(OFL). The luminol released by specific recognition between OFL and aptamer_(OFL) could not only react with •O₂^- but also produce chemiluminescence emission, resulting in the "signal-on" state. Because of the signal "on-off-on", the proposed aptasensor exhibited wide linear ranges for CIP (0.001-100 ng/mL) and OFL (0.0005-100 ng/mL) detection. Furthermore, the low detection limits of CIP (0.06 pg/mL) and OFL (0.022 pg/mL) could achieve the ultrasensitive analysis.

Self-Powered Photoelectrochemical Assay for Hg2+ Detection Based on g-C3N4-CdS-CuO Composites and Redox Cycle Signal Amplification Strategy

A highly sensitive self-powered photoelectrochemical (spPEC) sensing platform was constructed for Hg2+ determination based on the g-C3N4-CdS-CuO co-sensitized photoelectrode and a visible light-induced redox cycle for signal amplification. Through successively coating the single-layer g-C3N4, CdS, and CuO onto the surface of an electrode, the modified electrode exhibited significantly enhanced PEC activity. The microstructure of the material was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). However, the boost in photocurrent could be noticeably suppressed due to the consumption of hole-scavenging agents (reduced glutathione) by the added Hg2+. Under optimal conditions, we discovered that the photocurrent was linearly related to the Hg2+ concentration in the range of 5 pM–100 nM. The detection limit for Hg2+ was 0.84 pM. Moreover, the spPEC sensor demonstrated good performance for the detection of mercury ions in human urine and artificial saliva.

Dual Direct Z-Scheme Heterojunction with Growing Photoactive Property for Sensitive Photoelectrochemical and Colorimetric Bioanalysis

A dual direct Z-scheme heterojunction photoactive material of CoTiO₃/g-C₃N₄/Bi₂O₃ was designed based on calcination and in situ illumination-assisted process for sensitivity bioproteins detection which combined with MnO₂ nanoflowers to achieve signal quenching strategy. The complex consists of two direct Z-scheme heterojunctions of g-C₃N₄ and two photoactive materials CoTiO₃ and Bi₂O₃. This great structure could augment the migration of photogenerated electrons obviously, which boost the photocurrent greatly and prefer the photoelectric application of perovskite oxide. To improve sensitivity, the nanoflower like MnO₂ with oxidation performance is introduced into the system and used as a label fixed on secondary antibody to oxidize electron donor (AA) to achieve an enlarged signal quenching value. Interestingly, MnO₂ also showed an effective oxidation activity for TMB oxidation, leading to a chromogenic reaction. With the change of antigen concentration, the color of the test electrolyte also changes. Herein, the designed smart photoelectrochemical sensor shows a wide detection range (neuron specific enolase as an example) from 0.00005 to 200 ng/mL with a detection limit as low as 28 fg/mL. And the colorimetric assay for target detection owns a liner range from 0.1 to 20 ng/mL accompany with a detection limit of 0.05 ng/mL. These two designed sensing modes offer a new strategy for signal amplification of perovskite oxide and the possibility of real-time detection.

Sensitive photoelectrochemical determination of T4 polynucleotide kinase using AuNPs/SnS2/ZnIn2S4 photoactive material and enzymatic reaction-induced DNA structure switch strategy

We report here Au nanoparticles (AuNPs)/SnS₂/ZnIn₂S₄ as a high-performance active material for sensitive photoelectrochemical (PEC) determination of T4 polynucleotide kinase (T4 PNK) using an enzymatic reaction-induced DNA structure switch strategy. To construct the PEC biosensor, a double-stranded DNA probe consisting of a CdS quantum dots (QDs)-labeled single-stranded DNA (sDNA) and its complementary DNA (cDNA) is immobilized on the AuNPs/SnS₂/ZnIn₂S₄ photoactive material. T4 PNK can catalyze the phosphorylation of 5'-OH-terminated sDNA in the double-stranded DNA probe when ATP is present, and λ-exonuclease can catalyze the degradation of the phosphorylated sDNA into small fragments. Then the cDNA forms a hairpin structure so that CdS QDs and AuNPs are in close contact, which can induce exciton-plasma interactions between CdS QDs and AuNPs. The exciton-plasma interactions significantly boost the photocurrent, enabling the "signal on" PEC determination of T4 PNK in the range of 10^-4 - 1 U mL^-1 with a detection limit of 6 × 10^-5 U mL^-1. The PEC biosensor can also be used to screen enzyme inhibitors.

Framework-promoted charge transfer for highly selective photoelectrochemical biosensing of dopamine

Traditional photoelectrochemical (PEC) systems with inorganic semiconductors as photoactive materials generally involve effortless recombination of electron-hole pairs, which greatly limit the detection sensitivity. The arrangement of multiple components with tunable bandgaps provides an effective way to accelerate charge transfer. In this work, a framework material with adjustable structure was used to promote the charge transfer in the PEC process. The framework was constructed with 9,10-di(p-carboxyphenyl)anthracene (DPA) ligands as the light collector to coordinate with Zn²⁺ nodes, which formed an electronegative metal-organic framework (ZnMOF), and showed good conductivity and PEC performance due to the π-π stacking of DPA and the intrareticular charge transfer. Based on the band and charge matching of dopamine (DA) with ZnMOF, the ZnMOF modified electrode as a biosensor showed excellent PEC response to DA with good selectivity, thus realized sensitive detection of DA ranging from 0.03 to 10 μM with a detection limit of 17.7 nM. The biosensor could be used to monitor the release of DA from PC12 cells and evaluate the stimulation of K⁺ to DA release. The conductive framework material provided an approach to develop highly selective sensing platform for trace bioanalysis.

Construction of a photoelectrochemical immunosensor based on CuInS2 photocathode and BiVO4/BiOI/Ag2S photoanode and sensitive detection of NSE

In this paper, a photoelectrochemical (PEC) immunosensor was constructed to detect neuron-specific enolase (NSE) with ITO/BiVO₄/BiOI/Ag₂S as photoanode and ITO/CuInS₂ as photocathode. Due to its excellent photocurrent response, Ag₂S sensitized BiVO₄/BiOI composite was selected to provide stable photocurrent in place of the traditional Pt electrode. ITO/CuInS₂ electrode was used to immobilize biomolecules, which solved the deficiency of poor anti-interference ability of single photoanode. Under the optimal experimental conditions, the PEC immunosensor had outstanding linear relationship within the range of NSE concentration from 5 pg/mL-200 ng/mL, and the detection limit was 1.2 pg/mL. The constructed PEC immunosensor had two advantages. On the one hand, the PEC immunosensor was built on the photocathode, which had better anti-interference ability because of the separation of light capture and biomolecular recognition process. On the other hand, the introduction of photoanode increased the photocurrent response and reduced the detection limit of target antigen. The PEC immunosensor had good stability, reproducibility and specificity, and provided a broad prospect for the detection of other molecules.

A Colorimetric Immunoassay Based on g-C3N4@Fe3O4 Nanocomposite for Detection of Carcinoembryonic Antigen

We proposed a colorimetric immunosensor based on g-C₃N₄@Fe₃O₄ nanocomposite-mediated transformation strategy for sensitive detection of carcinoembryonic antigen (CEA). The g-C₃N₄@Fe₃O₄ nanocomposite was synthesized and characterized by the scanning electron microscope (SEM), energy dispersive X-ray spectra (EDX), X-ray powder diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Fe³⁺ derived from g-C₃N₄@Fe₃O₄ nanocomposite could combine with sodium salicylate to form purple complex products. Based on this color development, the sandwich colorimetric immunoassay was built by utilizing g-C₃N₄@Fe₃O₄ nanocomposite as nanolabels on the microplate. With the increasement of CEA concentration, the purple color showed a gradient change. Under optimal conditions, the linearity range is 0.001-50 ng/mL with the detection limit of 0.35 pg/mL for CEA. More importantly, the colorimetric immunoassay has good selectivity, specificity, repeatability, and stability.

A Comprehensive Review of Graphitic Carbon Nitride (g-C3N4)-Metal Oxide-Based Nanocomposites: Potential for Photocatalysis and Sensing

g-C3N4 has drawn lots of attention due to its photocatalytic activity, low-cost and facile synthesis, and interesting layered structure. However, to improve some of the properties of g-C3N4, such as photochemical stability, electrical band structure, and to decrease charge recombination rate, and towards effective light-harvesting, g-C3N4-metal oxide-based heterojunctions have been introduced. In this review, we initially discussed the preparation, modification, and physical properties of the g-C3N4 and then, we discussed the combination of g-C3N4 with various metal oxides such as TiO2, ZnO, FeO, Fe2O3, Fe3O4, WO3, SnO, SnO2, etc. We summarized some of their characteristic properties of these heterojunctions, their optical features, photocatalytic performance, and electrical band edge positions. This review covers recent advances, including applications in water splitting, CO2 reduction, and photodegradation of organic pollutants, sensors, bacterial disinfection, and supercapacitors. We show that metal oxides can improve the efficiency of the bare g-C3N4 to make the composites suitable for a wide range of applications. Finally, this review provides some perspectives, limitations, and challenges in investigation of g-C3N4-metal-oxide-based heterojunctions.

A Target-Driven Self-Feedback Paper-Based Photoelectrochemical Sensing Platform for Ultrasensitive Detection of Ochratoxin A with an In2S3/WO3 Heterojunction Structure

Currently, developing versatile, easy-to-operate, and effective signal amplification strategies hold great promise in photoelectrochemical (PEC) biosensing. Herein, an ultrasensitive polyvinylpyrrolidone-treated In₂S₃/WO₃ (In₂S₃-P/WO₃)-functionalized paper-based PEC sensor was established for sensing ochratoxin A (OTA) based on a target-driven self-feedback (TDSF) mechanism enabled by a dual cycling tactic of PEC chemical-chemical (PECCC) redox and exonuclease III (Exo III)-assisted complementary DNA. The In₂S₃-P/WO₃ heterojunction structure with 3D open-structure and regulable topology was initially in situ grown on Au nanoparticle-functionalized cellulose paper, which was served as a universal signal transducer to directly record photocurrent signals without complicated electrode modification, endowing the paper chip with admirable anti-interference ability and unexceptionable photoelectric conversion efficiency. With the assistance of Exo III-assisted cycling process, a trace amount of OTA could trigger substantial signal reporter ascorbic acid (AA) generated by the enzymatic catalysis of alkaline phosphatase, which could effectively provoke the PECCC redox cycling among the tris(2-carboxyethyl)phosphine acid, AA, and ferrocenecarboxylic at the In₂S₃-P/WO₃ photoelectrode, initiating TDSF signal amplification. Based on the TDSF process induced by the Exo III-assisted recycling and PECCC redox cycling strategy, the developed paper-based PEC biosensor realized ultrasensitive determination of OTA with persuasive selectivity, high stability, and excellent reproducibility. It is believed that the proposed paper-based PEC sensing platform exhibited enormous potential for the detection of other targets in bioanalysis and clinical diagnosis.

Recent Advances of Nanostructured Materials for Photoelectrochemical Bioanalysis

Nowadays, the emerging photoelectrochemical (PEC) bioanalysis has drawn intensive interest due to its numerous merits. As one of its core elements, functional nanostructured materials play a crucial role during the construction of PEC biosensors, which can not only be employed as transducers but also act as signal probes. Although both chemical composition and morphology control of nanostructured materials contribute to the excellent analytical performance of PEC bioassay, surveys addressing nanostructures with different dimensionality have rarely been reported. In this review, according to classification based on dimensionality, zero-dimensional, one-dimensional, two-dimensional, and three-dimensional nanostructures used in PEC bioanalysis are evaluated, with an emphasis on the effect of morphology on the detection performances. Furthermore, using the illustration of recent works, related novel PEC biosensing patterns with promising applications are also discussed. Finally, the current challenges and some future perspectives in this field are addressed based on our opinions.

Portable electrochemical biosensor based on laser-induced graphene and MnO2 switch-bridged DNA signal amplification for sensitive detection of pesticide

Developing portable, quantitative, and user-friendly analytical tools for sensitive pesticide assay is of significant importance for guaranteeing food safety. Herein, a novel electrochemical biosensor was constructed by integrating laser-induced graphene (LIG) electrode on polyimide (PI) foil and MnO₂ nanosheets loaded on the paper for point-of-care test (POCT) of organophosphorus (OPs) residues. The principle of this biosensor relied on acetylcholinesterase (AChE)-catalyzed hydrolytic product-triggered disintegration of MnO₂ nanosheets for releasing assistant DNA to initiate nicking enzyme-aided recycling amplification. In the presence of OPs, the activity of AChE was inhibited and could not initiate the cleavage of the electroactive molecules-labeled hairpin probe on the electrode, resulting in the maintenance of the electrochemical response to realize a "sign-on" determination of OPs. The proposed biosensor exhibited satisfactory analytical performance for OPs assay with a linear range from 3 to 4000 ng/mL and a limit of detection down to 1.2 ng/mL. Moreover, the biosensor was useful for evaluating the residual level of pesticides in the vegetables. Therefore, this novel biosensor holds great promise for OPs assay and opens a new avenue on the development of higher-performance POCT device for sensing applications in the environment and food safety fields.