Metal organic framework-derived CuO/Cu2O polyhedron-CdS quantum dots double Z-scheme heterostructure for cathodic photoelectrochemical detection of Hg2+ in food and environment

This study employed an innovative copper oxide/cuprous oxide (CuO/Cu2O) polyhedron‑cadmium sulphide quantum dots (CdS QDs) double Z-scheme heterostructure as a matrix for the cathodic PEC determination of mercury ions (Hg2+). First, the CuO/Cu2O polyhedral composite was prepared by calcining a copper-based metal organic framework (Cu-MOF). Subsequently, the amino-modified CuO/Cu2O was integrated with mercaptopropionic acid (MPA)-capped CdS QDs to form a CuO/Cu2O polyhedron-CdS QDs double Z-scheme heterostructure, producing a strong cathodic photocurrent. Importantly, this heterostructure exhibited a specifically reduced photocurrent for Hg2+ when using CdS QDs as Hg2+-recognition probe. This was attributed to the extreme destruction of the double Z-scheme heterostructure and the in situ formation of the CuO/Cu2O-CdS/HgS heterostructure. Besides, p-type HgS competed with the matrix for electron acceptors, further decreasing the photocurrent. Consequently, Hg2+ was sensitively assayed, with a low detection limit (0.11 pM). The as-prepared PEC sensor was also used to analyse Hg2+ in food and the environment.

Swellable microneedle-coupled light-addressable photoelectrochemical sensor for in-situ tracking of multiple pesticides pollution in vivo

In vivo monitoring of multiple pesticide contamination is of great significance for evaluating the health risks of different pesticides, agricultural production safety, and ecological and environmental assessment. Here, we report a hydrogel microneedle array coupled light-addressable photoelectrochemical sensor for tracking multiple pesticide uptake and elimination in living animals and plants, holding three prominent merits: i) enables in-situ detection of in vivo pesticides, avoiding cumbersome and complex sample transportation and handling processes; ii) allows repeated in vivo sampling of the same organism, improving tracking test controllability and accuracy; iii) avoids lethal sampling, providing a better understanding of the pesticides fate in living organisms. The coupled sensor is mechanically robust for withstanding more than 0.35 N per needle and highly swellable (800 %) for timely extraction of sufficient in vivo solution for analysis. For proof-of-concept, it achieves in-situ detection of atrazine, acetamiprid, and carbendazim efficiently and quantitatively in artificial agarose skin models, mouse skin interstitial fluids, and plant leaves with little inflammatory reaction. This simple, highly integrated, minimally invasive, and high-throughput in vivo monitoring method is ideal for future field environmental monitoring and plant and animal disease diagnosis.

Facile Semiconductor p-n Homojunction Nanowires with Strategic p-Type Doping Engineering Combined with Surface Reconstruction for Biosensing Applications

Photosensors with versatile functionalities have emerged as a cornerstone for breakthroughs in the future optoelectronic systems across a wide range of applications. In particular, emerging photoelectrochemical (PEC)-type devices have recently attracted extensive interest in liquid-based biosensing applications due to their natural electrolyte-assisted operating characteristics. Herein, a PEC-type photosensor was carefully designed and constructed by employing gallium nitride (GaN) p-n homojunction semiconductor nanowires on silicon, with the p-GaN segment strategically doped and then decorated with cobalt-nickel oxide (CoNiOx). Essentially, the p-n homojunction configuration with facile p-doping engineering improves carrier separation efficiency and facilitates carrier transfer to the nanowire surface, while CoNiOx decoration further boosts PEC reaction activity and carrier dynamics at the nanowire/electrolyte interface. Consequently, the constructed photosensor achieves a high responsivity of 247.8 mA W-1 while simultaneously exhibiting excellent operating stability. Strikingly, based on the remarkable stability and high responsivity of the device, a glucose sensing system was established with a demonstration of glucose level determination in real human serum. This work offers a feasible and universal approach in the pursuit of high-performance bio-related sensing applications via a rational design of PEC devices in the form of nanostructured architecture with strategic doping engineering.

Molecularly imprinted polymer photoelectrochemical sensor for the detection of triazophos in water based on carbon quantum dot-modified titanium dioxide

Widely used organophosphorus pesticide triazophos (TAP) can easily cumulate in aquatic system due to its high stability chemically and photochemically and thus posing significant threat to aquatic creatures and humans' health. Urging demand for rapid determining TAP in water has risen. Photoelectrochemical (PEC) sensing turns out to be a good candidate for its simplicity in fabrication and swiftness in detection. Nevertheless, traditional PEC sensors often lack selectivity as their signal generation primarily relies on the oxidation of organic compounds in the electrolyte by photo-induced holes. To address this limitation, molecularly imprinted polymers (MIPs) can be in combined with PEC sensors to significantly enhance the selectivity. Here, we present a novel approach utilizing a PEC sensor enhanced by carbon-modified titanium dioxide molecularly imprinted polymers (MIP/C/TiO2 NTs). Carbon quantum dot (CQD) modification of titanium dioxide nanotube arrays (C/TiO2 NTs) was achieved through a one-step anodization process, effectively enhancing visible light absorption by narrowing the band gap of TiO2, and CQDs also function as sensitizer accelerating charge transfer for improved and stable photocurrent signals during detection. Our method further incorporates MIPs to heighten the selectivity of the PEC sensor. Electro-polymerization using cyclic voltammetry was employed to polymerize MIPs with pyrrole as the functional monomer and triazophos as the target molecule. The resultant MIP/C/TiO2 NT sensor exhibited remarkable sensitivity, with a detection limit of 0.03 nM (S/N = 3), alongside exceptional selectivity and stability for triazophos detection in water. This offers a promising avenue for efficient, cost-effective, and rapid monitoring of pesticide contaminants in aquatic environments, contributing to the broader goals of environmental preservation and public health.

A photoelectrochemical sensor based on In2O3/In2S3/ZnIn2S4 ternary Z-scheme heterojunction for ultrasensitive detection of dopamine in sweat

A novel ternary heterojunction material In2O3/In2S3/ZnIn2S4 was synthesized, and a photoelectrochemical sensor was fabricated for the non-invasive test of dopamine (DA) in sweat. In2O3 multihollow microtubules were synthesized and then In2S3 was formed on their surface to construct a type-I heterojunction between In2S3 and In2O3. ZnIn2S4 was further introduced to form a Z-scheme heterojunction between In2S3/ZnIn2S4. Under photoexcitation, the photogenerated holes of In2O3 transferred to the valence band of In2S3, superimposed with the holes produced by In2S3, leads to a significantly higher photocatalytic oxidation capacity of In2O3/In2S3/ZnIn2S4 ternary composites than that of In2O3/In2S3. The Z-scheme heterojunction accelerates the transfer of photogenerated electrons accumulated on the type-I heterojunction. In the presence of DA, it is rapidly oxidized into polydopamine (PDA) by In2O3/In2S3, and the benzoquinone groups of PDA compete for the photogenerated electrons to reduce the current in the external circuit, whereby DA determination is achieved. Owing to the combination of type-I and Z-scheme heterojunction, the sensor showed extremely high sensitivity, with a detection limit of 3.94 × 10-12 mol/L. It is one of the most sensitive methods for DA detection reported and has been applied to the determination of DA in human sweat.

Wavelength-dependent photoelectrochemical response demonstrated by the determination of acetaminophen and rutin in differential molecularly imprinted polymers strategy

Herein, the excitation wavelength-dependent responses of the molecularly imprinted polymer (MIP) photoelectrochemical (PEC) sensors were investigated, using acetaminophen (AP), rutin (RT) and perfluorooctanoate (PFOA) as the model templates, pyrrole as functional monomer, CuInS2@ZnS/TiO2 NTs as the basic photoelectrode. With wavelength λ > 240 nm, the photocurrent of MIPPFOA enhanced at higher concentrations of PFOA. With increasing AP concentration, the photocurrents of MIPAP could decline with λ < 271 nm, not change at λ = 270 nm, or increase with λ > 270 nm. As RT concentration increased, the photocurrents of MIPRT could decrease (λ < 431 nm), not change (λ = 431 nm) or increase (λ > 431 nm). The PEC responses depend on the comprehensive interaction of two contrary mechanisms from the template molecules within the MIP membrane. The photocurrent is enhanced by the role of the electron donor for photo-generated holes but attenuated due to the steric hindrance effect and the excitation light intensity loss via absorption or scattering. The apparent molar absorption coefficient of AP and RT within MIP membranes are 9.1-19.4 folds of those measured from dilute solutions. By using a routine UV lamp as the light source, the photocurrents of MIPRT at 254 nm and MIPAP at 365 nm were used to determine RT and AP, with the detection limits of 5.3 and 16 nM, respectively. The interference from the non-specific adsorption of interferents on the surfaces of MIPAP and MIPRT was reduced by one order of magnitude via a differential strategy.

A platform for microplastic assessment in aquatic environments based on the protein corona-induced aggregation effect

The environmental hazards of microplastics have received widespread attention. However, the in-situ detection of microplastics, particularly in aquatic environments, has been challenged by the limitations of detection methods, the large-scale instruments, and small size. Herein, a photoelectrochemical sensor based on the protein corona-induced aggregation effect is designed for the detection of polystyrene microplastics. The sensor has advantages of high sensitivity, reproducibility, and detection capability. A linear detection range of 0.5-500 μg mL-1, a method detection limit of 0.06 μg mL-1, and a limit of quantification of 0.14 μg mL-1 are achieved. Furthermore, the relative standard deviations of intra-day and inter-day precision, ranging from 0.56% to 4.63% and 0.84%-3.36% are obtained. A digital multimeter was employed to construct a platform for the real-time detection in real water samples, streamlining the detection process and yielding clear results. We believe this sensor provides new insight for the in-situ real-time detection of microplastics and has broad applications for the analysis of microplastic pollution in aquatic environments.

Ti3C2@UiO-TCPP Schottky junction photoelectrochemical sensor for detecting alkaline phosphatase through the steric hindrance effect of phosphopeptide

Alkaline phosphatase (ALP) is a major biomarker for clinical diagnosis, but detection methods of ALP are limited in sensitivity and selectivity. In this paper, a novel method for ALP determination is proposed. A photoelectrochemical (PEC) sensor was prepared by growing UiO-tetratopic tetrakis (4-carbox-yphenyl) porphyrin (TCPP) in situ between layered Ti3C2 through a one-pot hydrothermal method. The obtained Schottky heterojunction photoelectric material Ti3C2@UiO-TCPP not only has a large light absorption range but also greatly improves the efficiency of photogenerated electron hole separation and thereby enhances sensitivity for PEC detection. The phosphate group on the phosphorylated polypeptide was utilized to form a Zr-O-P bond with the zirconium ion on UiO-66, and then photocurrent decreases due to the steric hindrance effect of phosphorylated polypeptides, that is, the hindrance of electron transfer between the photoelectric material and a solution. The specific interaction between ALP and phosphorylated polypeptides shears the bond between phosphate and zirconium ion on UiO-66 in the peptides then weakens the hindrance effect and increases the photocurrent, thus realizing ALP detection. The linear range of ALP is 0.03-10,000 U·L-1, and the detection limit is 0.012 U·L-1. The method is highly sensitive and selective, and has been applied in detection of ALP in serum samples.

ZnO/Au/GaN heterojunction-based self-powered photoelectrochemical Sensor for alpha-fetoprotein detection

In recent years, the development of miniature and portable sensors has been a major focus of research. PEC self-powered sensors have emerged as a potential solution to the power supply issue, eliminating the need for external power supplies and operating without bias voltage. This study developed a ZnO/Au/GaN sensor for highly sensitive detection of alpha-fetoprotein (AFP). The sensor uses GaN substrates with nanogold films to provide an auxiliary bias voltage, promoting high photogenerated current density. Using ZnO/Au/GaN as a photoanode resulted in significantly higher photocurrent generated by the sensor compared to Au/GaN or ZnO/ITO alone. To enable selective detection of AFP, antibody modification of the ZnO nanorod arrays was employed. The linear range of the sensor response to AFP was determined to be 0.080-5.0 ng/mL, with an impressively low detection limit of 0.027 ng/mL (S/N = 3). These results demonstrate the potential of this self-powered sensor for detecting AFP content in human serum samples. Overall, this study presents a novel approach for developing highly sensitive and selective self-powered sensors for biomarker detection, which could facilitate early detection and clinical diagnosis of various types of cancer.

A responsive organic probe based photoelectrochemical sensor for hydrazine detection

This study developed a new photoelectrochemical (PEC) sensor for the detection of the hydrazine (N2H4, HZ) based on a donor-π-bridge-acceptor (D-π-A) configuration organic photoactive dye (Dye-HZ). The dye was covalently immobilized on an FTO/TiO2 (FTO: fluorine-doped tin oxide) substrate, resulting in a photoanode FTO/TiO2/Dye-HZ that exhibits a specific PEC response to N2H4. Hydrazine reacts with the acetyl group in the Dye-HZ molecule, leading to its removal and the formation of a hydroxy group. The hydroxy group dissociates a hydrogen ion, forming a phenoxide anion with strong electron-donating characteristics. As a result, the dye molecule exhibits a strong intramolecular charge transfer effect, significantly enhancing absorbance and photoelectric response under visible light irradiation, leading to a remarkable increase in photocurrent and enabling highly sensitive detection of hydrazine. Furthermore, the PEC sensor demonstrates excellent selectivity and can be applied for the detection of hydrazine in real water samples. This study presents an innovative PEC sensing approach for hydrazine based on responsive photoactive molecules, providing new insights for PEC detection of other environmental pollutants.

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

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

A universal CRISPR-Cas14a responsive triple-sensitized upconversion photoelectrochemical sensor

It has recently been discovered that, like other members of the Cas family (12a and 13a), the clustered regularly interspaced short palindrome repeat CRISPR-Cas14a system not only mediates high-sensitivity detection with exceptionally strong gene editing ability but is also generally useful for DNA detection via fluorescence. Photoelectrochemical (PEC) sensors have been widely applied as efficient analytical tools. Measuring electrical signals is more cost-effective and the necessary equipment is more easily portable than fluorescence signal detectors, but their stability still needs to be improved. The high base resolution of CRISPR-Cas14a can compensate for such shortcomings. Therefore, electrical signals and fluorescence signals were combined, and the development of a universal CRISPR-Cas14a-responsive ultrasensitive upconversion PEC sensor is described in this paper. Moreover, strand displacement amplification (SDA) and a near-infrared (NIR) light source were utilized to further improve the stability and sensitivity of the photoelectric signals. At the same time, the modified working electrode (UCNPs-ssDNA-CdS@Au/ITO) on the three-electrode disposable sensor was used as the reporter probe, which cooperates with the trans-cleavage activity of Cas14a endonuclease. To verify the universality of this sensor, the UCNPs-Cas14a-based PEC sensor was applied for the detection of the small-molecule toxin T2 and protein kinase PTK7. Here, we report that the limit of detection of this reagent was within the fg range, successfully applied to the detection of T2 in oats and PTK7 in human serum. We propose that by combining PEC and CRISPR-14a, UCNPs-Cas14a-based PEC sensors could become powerful drivers for the extensive development of ultrasensitive, accurate and cost-effective universal sensors for detection and diagnosis.

A smartphone-powered photoelectrochemical POCT via Z-scheme Cu2O/Cu3SnS4 for dibutyl phthalate in the environmental and food

As a major hazardous additive released from microplastics and nanoplastics, identifying dibutyl phthalate (DBP) in complex matrices attracts a growing concern in environmental monitoring and food safety. For the first time, Cu2O/Cu3SnS4 nanoflower is prepared and serves as the photoactive material which can be constructed as a smartphone-based photoelectrochemical (PEC) point-of-care test (POCT). Effectively matching energy levels between Cu2O and Cu3SnS4 accelerated the transfer of photogenerated electron-hole pairs, significantly improving the intelligent PEC POCT performance. The novel Cu2O/Cu3SnS4 has proven to be the Z-scheme heterojunction by density functional theory calculation. A competitive immunoassay has been realized on a Cu2O/Cu3SnS4 modified electrode, dramatically decreasing the photocurrent signal and enhancing POCT sensitivity. The smartphone has been used to record and transfer PEC results. Under optimal conditions, the PEC POCT exhibited a satisfying linear range (0.04-400 ng/mL) and a low detection limit of 7.94 pg/mL in real samples, together with excellent stability, repeatability, reproducibility and selectivity. The PEC POCT system provides good performance and practicability in determining DBP in water and edible oil samples. This proposal provides a practical strategy for the intelligent POCT for environment monitoring and food safety.

A highly selective self-powered sensor based on the upconversion nanoparticles/CdS nanospheres for chlorpyrifos detection

Light sources are crucial for photoelectrochemical (PEC) self-powered sensing, where visible light is widely used. However, due to its high energy, it has some downsides as an irradiation source for overall system, so it is urgent to achieve effective near-infrared (NIR) light absorption because it makes up a significant portion of the solar spectrum. Herein, up-conversion nanoparticles (UCNPs) that could increase the energy of low-energy radiation were combined with semiconductor CdS as the photoactive material (UCNPs/CdS), which broadens the response range of solar spectrum. The NIR light-excited self-powered sensor could be produced via oxidizing H2O at photoanode and lowering dissolved oxygen at cathode under the NIR light without external voltage. Meanwhile, molecularly imprinted polymer (MIP) was added to photoanode as a recognition element to increase the sensor's selectivity. The open-circuit voltage of the self-powered sensor grew linearly as chlorpyrifos concentration climbed from 0.01 to 100 ng mL-1, showing good selectivity as well as reproducibility. This work provides valuable basis for the preparation of efficient and practical PEC sensor with NIR light response.

Molecularly imprinted ultrasensitive cholesterol photoelectrochemical sensor based on perfluorinated organics functionalization and hollow carbon spheres anchored organic-inorganic perovskite

In spite of organic-inorganic perovskite emerging as a novel efficient light-harvesting material owing to their superior optical properties, excitonic properties, and electrical conductivity, the related applications are severely limited for their poor stability and selectivity. Herein, we introduced hollow carbon spheres (HCSs) and 2-(perfluorohexyl) ethyl methacrylate (PFEM) based molecularly imprinted polymers (MIPs) to dual-functionalize CH3NH3PbI3. HCSs can provide perovskite load conditions, passivate perovskite defects, increase carrier transport and effectively improve its hydrophobicity. The perfluorinated organic compound based MIPs film can not only enhance the water and oxygen stability of perovskite, but also endow it specific selectivity. Moreover, it can reduce the photoexcited electron-hole pair recombination and prolong the electron lifetime. Benefiting from the synergistic sensitization of HCSs and MIPs, an ultrasensitive photoelectrochemical platform (MIPs@CH3NH3PbI3@HCSs/ITO) for cholesterol sensing was acquired with a very wide linear range of 5.0 × 10-14-5.0 × 10-8 mol/L and an extremely low detection limit of 2.39 × 10-15 mol/L. The designed PEC sensor exhibited good selectivity and stability, as well as practicality for real sample analysis. The present work extended the development of the high-performance perovskite and showed its broad application prospect for advanced PEC construction.

Photoelectrochemical detection of superoxide anions released from mitochondria in HepG2 cells based on the synergistic effect of MnO2@Co3O4 core-shell p-n heterojunction

The detection and comparison of the amount of superoxide anion (O2.-) released by different complexes in mitochondrial electron transport chain (ETC) can locate the main electron leakage sites in mitochondria. In order to realize this, we designed an ultrasensitive photoelectrochemical (PEC) sensor by in situ hydrothermal growth of MnO2 nanosheets on Co3O4 nanowires array modified Ti substrate (NWA|Ti). Due to the formation of a core-shell p-n heterojunction with high specific surface area, tight surface contact and plentiful oxygen vacancies (OVs), MnO2@Co3O4 NWA|Ti possesses a strong visible light absorption, high charges transfer and separation ability. The proposed PEC sensor exhibited a wide linear range of 0.1-50000 nM and a low detection limit of 0.025 nM towards H2O2. Due to the rapid conversion of O2.- to H2O2 inside mitochondria, the PEC sensor can indirectly monitor the electron leakage in the ETC. Specifically, four selected mitochondrial inhibitors specifically inhibited the corresponding complex in mitochondria extracted from living HepG2 cells (hepatocellular carcinoma cells), and the H2O2 levels converted from O2.- was measured by the PEC sensor. It is evident that IQ (ubiquinone binding) site of complex I and Qo (ubiquinol oxidation) site of complex III are the key sites at which electron leakage occurred. This study could provide meaningful information for the diagnosis and treatment of certain disease caused by oxidative stress due to the electron leakage.

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.

An ultra-sensitive photoelectrochemical sensor for chlorpyrifos detection based on a novel BiOI/TiO2 n-n heterojunction

Due to widespread application of chlorpyrifos for controlling pests in agriculture, the continuous accumulation of chlorpyrifos residue has caused serious environmental pollution.The detection of chlorpyrifos is of great significance for humans and environment because it can arise a series of diseases by inhibiting acetylcholinesterase (AChE) activity. Photoelectrochemical sensing, as an emerging sensing technology, has great potential in the detection of chlorpyrifos. It is urgent that find a suitable photoelectric sensing strategy to effectively monitor chlorpyrifos. Herein, an n-n heterojunction was constructed by uniformly immobilizing n-type 3DBiOI, which had loose porous structure composed of numerous small and thin nanosheets, on the surface of TiO₂ with anatase/rutile (AR-TiO₂) heterophase junction. Under light irradiation, the proposed BiOI/AR-TiO₂ n-n heterojunction exhibited excellent optical absorption characteristics and photoelectrochemical activity. Additionally, the photoelectrochemical sensing platform demonstrated excellent analytical performance in monitoring chlorpyrifos. Under optimized conditions, it showed a wide detection range of 1 pg mL^-1- 200 ng mL^-1 and a detection limit (S/N = 3) as low as 0.24 pg mL^-1, with superior selectivity and stability. The ultra-sensitivity and great specificity for detection of chlorpyrifos can be ascribed to chelation between Bi (Ⅲ) and C=N and P=S bonds in chlorpyrifos, which had been confirmed in this work. Meanwhile, the PEC sensor also had potential application value for monitoring chlorpyrifos in water samples, lettuce and pitaya, which the recoveries of samples ranged from 96.9% to 104.7% with a relative standard deviation (RSD) of 1.11%-5.93%. This sensor provided a novel idea for constructing heterojunctions with high photoelectric conversion efficiency and had a high application prospect for the detection of chlorpyrifos and other structural analogues.

Detection of L-cysteine in urine samples based on CdS/TiO2-modified extended-gate field-effect transistor photoelectrochemical sensor

A novel extended-gate field-effect transistor (FET) photoelectrochemical (EGFET PEC) sensor was designed for highly sensitive detection of L-cysteine (L-Cys). TiO2 was initially modified on the ITO electrode by the sol-gel dip-coating method and calcined to produce TiO2/ITO. Then, CdS was synthesized on the TiO2 surface by hydrothermal method to obtain the CdS-TiO2 heterojunction material. CdS/TiO2/ITO was connected to the gate of the FET to obtain an EGFET PEC sensor. Under the irradiation of a xenon lamp simulating visible light, the CdS/TiO2 heterojunction composite absorbs light energy to produce photogenerated electron-hole pairs, which have strong photocatalytic oxidation activity and oxidize L-Cys covalently identified by Cd(II) through CdS covalent. These pairs generate a photovoltage that controls the current between the source and the drain to detect L-Cys. Under the optimized experimental conditions, the optical drain current (ID) of the sensor exhibited a good linear relationship with the logarithm of L-Cys in the range of 5.0 × 10-9-1.0 × 10-6 mol/L, and the detection limit was 1.3 × 10-9 mol/L (S/N = 3), which is lower than the values reported by other detection methods. Results showed that the CdS/TiO2/ITO EGFET PEC sensor revealed high sensitivity and good selectivity. The sensor has been used to determine L-Cys in urine samples.

Sensitive photoelectrochemical immunosensor for carcinoembryonic antigen detection based on copolymer of thiophene and thiophene-3-acetic acid modified phosphate-doped Bi2WO6

In this study, PO₄^3- doped Bi₂WO₆ (BWO-PO) was prepared by hydrothermal method, and then copolymer of thiophene and thiophene-3-acetic acid (P(Th-T3A)) was chemically deposited on the BWO-PO surface. The introduction of PO₄^3- created point defects, greatly improving the photoelectric catalytic performance of Bi₂WO₆; the copolymer semiconductor could form heterojunction with Bi₂WO₆ to promote the separation of photo-generated carriers, due to its proper band gap. Furthermore, the copolymer could enhance the light absorption ability and photo-electronic conversion efficiency. Hence, the composite had good photoelectrochemical properties. When it was combined with carcinoembryonic antibody through the interaction of -COOH groups of the copolymer and the end groups of antibody for constructing ITO-based PEC immunosensor, the resulting sensor exhibited superb response to carcinoembryonic antigen (CEA), with a wide linear range of 1 pg/mL-20 ng/mL, and a relatively low detection limit of 0.41 pg/mL. It also showed high anti-interference ability, stability, and simplicity. The sensor has been successfully applied to monitor the concentration of CEA in serum. The sensing strategy can also be applied to the detection of other markers by changing the recognition elements, hence it has good application potential.

Au/TiO2-based molecularly imprinted photoelectrochemical sensor for dibutyl phthalate detection

A photoelectrochemical molecular imprinting sensor based on Au/TiO₂ nanocomposite was constructed for the detection of dibutyl phthalate. Firstly, TiO₂ nanorods were grown on fluorine-doped tin oxide substrate by hydrothermal method. Then, gold nanoparticles were electrodeposited on TiO₂ to fabricate Au/TiO₂. Finally, molecular imprinted polymer was electropolymerized on the Au/TiO₂ surface to construct MIP/Au/TiO₂ PEC sensor for DBP. The conjugation effect of MIP accelerates the electron transfer between TiO₂ and MIP, which can greatly improve the photoelectric conversion efficiency and sensitivity of the sensor. In addition, MIP can also provide sites for highly selective recognition of dibutyl phthalate molecules. Under optimal experimental conditions, the prepared photoelectrochemical sensor was used for the quantitative determination of DBP and the results showed a wide linear range (50 to 500 nM), a low limit of detection (0.698 nM), and good selectivity. The sensor was used in a study of real water samples to show that it has promising applications in environmental analysis.

Covalent organic framework: A state-of-the-art review of electrochemical sensing applications

Covalent organic framework (COF), a kind of porous polymer with crystalline properties, is a periodic porous framework material with precise regulation at atomic level, which can be formed by the orderly connection of pre-designed organic construction units through covalent bonds. Compared with metal-organic frameworks, COFs exhibit unique performance, including tailor-made functions, stronger load ability, structural diversity, ordered porosity, intrinsic stability and excellent adsorption features, are more conducive to the expansion of electrochemical sensing applications and the universality of applications. In addition, COFs can accurately integrate organic structural units with atomic precision into ordered structures, so that the structural diversity and application of COFs can be greatly enriched by designing new construction units and adopting reasonable functional strategies. In this review, we mainly summarized state-of-the-art recent advances of the classification and synthesis strategy of COFs, the design of functionalized COF for electrochemical sensors and COFs-based electrochemical sensing. Then, an overview of the considerable recent advances made in applying outstanding COFs to establish electrochemical sensing platform, including electrochemical sensor based on voltammetry, amperometry, electrochemical impedance spectroscopy, electrochemiluminescence, photoelectrochemical sensor and others. Finally, we discussed the positive outlooks, critical challenges and bright directions of COFs-based electrochemical sensing in the field of disease diagnosis, environmental monitoring, food safety, drug analysis, etc.

Polyacrylic acid/polyethylene glycol hybrid antifouling interface for photoelectrochemical immunosensing of CYFRA 21-1 based on TiO2/PpIX/Ag@Cu2O composite

A photoelectrochemical (PEC) transducer based on composite TiO₂/PpIX/Ag@Cu₂O was prepared for the detection of CYFRA 21-1. TiO₂ nanomaterials were synthesized by hydrothermal method. TiO₂/PpIX/Ag@Cu₂O composites were obtained by combining protoporphyrin Ⅸ (PpIX) molecules and Ag@Cu₂O on TiO₂. This composite material has strong absorption in visible light region and excellent photoelectric chemical properties. Ascorbic acid (AA) is a good electron donor, which can remove photogenerated holes in liquid environment to inhibit the recombination of photogenerated electrons and hole pairs, thus enhancing the photocurrent and improving its stability. The results showed that the sensor can quantitatively test CYFRA 21-1 in the range of 0.1 pg/mL∼100 ng/mL. The photoelectric chemical sensor has the advantages of high sensitivity, low detection line limit and wide linear range.

Codoping g-C3N4 with boron and graphene quantum dots: Enhancement of charge transfer for ultrasensitive and selective photoelectrochemical detection of dopamine

The development of superior photoelectrochemical (PEC) sensors for biosensing has become a major objective of PEC research. However, conventional PEC-active materials are typically constrained by a weak photocurrent response owing to their limited surface-active sites and high electron-hole recombination rate. Here, a boron and graphene quantum dots codoped g-C₃N₄ (named GBCN) as PEC sensor for highly sensitive dopamine (DA) detection was fabricated. GBCN exhibited the greatest photocurrent response and PEC activity compared to free g-C₃N₄ and g-C₃N₄ doped with boron. The proposed PEC sensor for DA determination exhibited a broad linear range (0.001-800 μM) and a low detection limit (0.96 nM). In particular, a sensitivity up to 10.3771 μA/μM/cm² was seen in the case of GBCN. The high PEC activity can be attributed to the following factors: (1) the boron and graphene quantum dots co-doping significantly increased the specific surface area of g-C₃N₄, providing more adsorption sites for DA; (2) the dopants extended the absorption intensity of g-C₃N₄, red-shifting the absorption from 470 to 540 nm; and (3) the synergism of boron and graphene quantum dots efficiently boosted the photogenerated electrons migration from the conduction band of g-C₃N₄ to graphene quantum dots, facilitating charge separation. In addition, GBCN also exhibited good anti-interference ability and stability. This research may shed light on the creation of a highly sensitive and selective PEC platform for detecting biomolecules.

Growth of AgI semiconductors on tailored 3D porous Ti3C2 MXene/graphene oxide aerogel to develop sensitive and selective "signal-on" photoelectrochemical sensor for H2S determination

Long term exposure to hydrogen sulfide (H₂S) even in low concentration poses a serious threat to human health and the ecosystem, pointing to the significance for its effective supervision. In this study, we report a sensitive and selective "signal-on" photoelectrochemical (PEC) sensor for the determination of toxic H₂S in aqueous solution by in situ growth of AgI semiconductors on tailored three-dimensional (3D) porous Ti₃C₂ MXene/graphene oxide aerogel (MGA). Our research demonstrated that the resultant MGA with the starting feeding mass ratio of MXene and graphene oxide (GO) of 1:8 (MGA_1:8) possessed the most excellent PEC performance after the growth of AgI semiconductors than their monomers (Ti₃C₂ MXene and GO) and the MGAs with other starting feeding mass ratio. Such designed PEC sensor based on MGA_1:8/AgI heterojunction showed dramatically strengthened PEC responses with increasing concentrations of S^2-. Correspondingly, a wide linear range of 5 nM-200 μM, a low limit of detection of 1.54 nM (S/N = 3), and exclusively unique selectivity have been achieved. Our research illustrates that the PEC sensor designed with tailored MGA constitutes is an effective pathway to enhance the overall sensing performance, which will envision to boost more efforts for advanced 3D porous aerogel using in PEC sensors.

MOF/COF heterostructure hybrid composite-based molecularly imprinted photoelectrochemical sensing platform for determination of dibutyl phthalate: A further expansion for MOF/COF application

A novel metal-organic framework (MOF)/covalent-organic framework (COF) heterostructure hybrid composite (NH₂-UiO-66/TpPa-1-COF) with excellent photoactivity was developed, which further acted as the photoelectrochemical sensitized layer of a molecularly imprinted photoelectrochemical (MIP-PEC) sensor for extremely sensitive and selective determination of dibutyl phthalate (DBP). The NH₂-UiO-66/TpPa-1-COF was synthesized using a simple one-step solvothermal method, which showed improved photocurrent response owing to heterojunction formation, favorable energy-band configuration and strong light absorption capacity. To improve the sensing performance, molecularly imprinted polymer (MIP) was developed by sol-gel polymerization method as the recognition component of PEC sensor. The specific binding of imprinting sites towards DBP could block the electron transfer, causing decreased photocurrent response of the MIP-PEC sensor. The MIP-PEC sensor showed a wide detection range from 0.1 nmol L^-1 to 100 μmol L^-1 with a limit of detection of 3.0 × 10^-11 mol L^-1 under optimal conditions. Meanwhile, the proposed MIP-PEC sensor showed good stability, selectivity, reproducibility, and applicability in real samples. This is the first attempt to apply MOF/COF heterostructure hybrid composite for MIP-PEC sensor construction, providing new insight into the potential applications of microporous crystalline framework heterostructure hybrid composite in the sensing field.

A novel photoelectrochemical sensor based on flower-like SnS2, sea urchin-like AgBiS2 and graphene oxide nanocomposite film for efficient and sensitive detection of acetaminophen in lake water samples

As an emerging detection technology, photoelectrochemical sensors have been widely noticed for their unique technical features. Among others, the technology has been widely used in the fields of drug, biological antibody or antigen and contaminant detection. Secondly, acetaminophen, as a novel environmental pollutant, is difficult to be degraded in the ecosystem, which in turn causes serious impacts on the ecosystem. Therefore, in this work, we designed a photoelectrochemical sensor based on a composite film of flower-like SnS₂, sea urchin-like AgBiS₂ and graphene oxide for the detection of acetaminophen in water samples. Among them, graphene oxide, as a two-dimensional carbon-based material, can immobilize other photoelectric materials well. In addition, the flower-like SnS₂ and sea urchin-like AgBiS₂ can enhance the intensity of the photoelectric response due to their synergistic effect. Notably, the combination of graphene oxide with SnS₂ and AgBiS₂ revealed an exponential increase in the photoresponse intensity, indicating that SnS₂/AgBiS₂/GO has a satisfactory photoresponse intensity. At the same time, the photoelectrochemical sensor exhibited sensitive detection performance (LOD = 4 nM) and a wide detection range (0.01-50 μM) for acetaminophen under optimal detection conditions. Moreover, it also showed excellent detection performance in the detection of actual water samples, indicating that it can be applied to the detection of acetaminophen in lakes.

A non-enzymatic photoelectrochemical sensor based on g-C3N4@CNT heterojunction for sensitive detection of antioxidant gallic acid in food

Gallic acid (GA) is found in a wide range of natural plants and is relevant to the health of human beings. Here, a photoelectrochemical sensing platform based on g-C₃N₄@CNT heterojunction has been prepared for the highly sensitive and selective detection of GA. Under the light of xenon lamp, the photocurrent of g-C₃N₄@CNT is 7 times higher than that of g-C₃N₄. And the sensor generates 4 times more photocurrent in the presence of GA than without GA. This sensor has a wide linear range from 10 nM to 10 μM with a limit of detection as low as 2 nM. Also, the abundant amino groups of g-C₃N₄ provide excellent selectivity for the sensor. Furthermore, the sensor can be used for the analysis of GA in black tea samples, which provides a novel and rapid method for the detection of GA in food samples.

A novel photoelectrochemical microfluidic chip for multi-index determination of diabetes and its complications

Rapid and accurate monitoring of glucose, lactic acid, pyruvic acid, and 3-hydroxybutyric acid is essential in preventing, diagnosing, and treating diabetes, lactic acidosis and diabetic ketoacidosis. Herein, a novel sensing chip for multi-index determination of diabetes, lactic acidosis, and diabetic ketoacidosis was presented by integrating microfluidic device and photoelectrochemical (PEC) sensor. In order to block the interference from the reductive species in real samples, the PEC sensor was divided into a biocathode and a photoanode, which were installed separately in the upper and bottom layers of the device. The photoanodes were modified with ZnIn₂S₄ nanoflower as photosensitive material, while enzymes for catalyzing the analytes were immobilized on the biocathodes. The PEC chip displayed wide detection ranges with low detection limits of 0.035 μM, 0.34 μM, 3.3 μM and 0.035 μM for the four analytes (S/N = 3). The chip also demonstrated decent anti-interference capability and reliability in monitoring the four biomarkers in human serum. Furthermore, a household amperemeter was deployed to record the photocurrent signals, which helps to reduce the cost. By replacing the enzyme on the biocathode, the sensing chip could play a role in monitoring a broad range of species.

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.

A label-free photoelectrochemical sensor of S, N co-doped graphene quantum dot (S, N-GQD)-modified electrode for ultrasensitive detection of bisphenol A

S, N co-doped graphene quantum dot (S, N-GQD) materials have been composited via a one-pot pattern and used as photosensitive materials to construct a label-free photoelectrochemical (PEC) sensor. The PEC experiments show an enhanced photocurrent response toward Bisphenol A (BPA) sensing due to the increased charge transfer rate and the enhanced absorption of visible light. Compared with dark conditions, the photocurrent signal (- 0.2 V vs. SCE) is greatly increased because of the effective oxidation of BPA by photogenerated holes and the rapid electron transfer of S, N-GQDs on the PEC sensing platform. Under optimal conditions linear current response to BPA is in two ranges of 0.12-5 µM and 5-40 µM. The limit of detection is 0.04 µM (S/N = 3). The designed sensor has enduring stability and admirable interference immunity. It  provides an alternative approach for BPA determination in real samples with recoveries of 99.3-103% and  RSD of 2.0-4.1%.

Self-powered photoelectrochemical aptasensor based on MIL-68(In) derived In2O3 hollow nanotubes and Ag doped ZnIn2S4 quantum dots for oxytetracycline detection

A self-powered photoelectrochemical (PEC) aptasensor was constructed based on MIL-68(In) derived indium oxide hollow nanotubes (In₂O₃ HNs) and Ag-doped ZnIn₂S₄ quantum dots (QDs) as sensing matrix for the ultrasensitive detection of oxytetracycline (OTC). The hollow tube structure of the designed photoelectric active platform provided abundant active sites and a larger specific surface area for the immobilization of target recognition unit. The coupling of Ag:ZnIn₂S₄ QDs and In₂O₃ HNs can accelerate the transmit and separation of photoinduced charge, and thus greatly increasing the intensity of photocurrent signal. Then, the well-constructed OTC-aptamer was anchored on the modified photoelectrode as an accurate capturing element, achieving the specific detection of analyte. Under optimal conditions, the photocurrent intensity of the PEC aptasensor decreases linearly, with a linear response range of 10^-4 -10 nmol/L, and a limit of detection (LOD) of 3.3 × 10^-5 nmol/L (S/N = 3). The developed self-powered aptasensor with excellent reproducibility, stability, and selectivity, provides a potential way to detect antibiotic residues in environmental media.

Light responsive Fe-Tcpp@ICG for hydrogen peroxide detection and inhibition of tumor cell growth

In this work, we synthesized Fe-Tcpp@ICG(ICG, Indocyanine green) with light stimuli-response through 5,10,15,20-tetrakis (4-carboxyphenyl) porphyrin (Fe-Tcpp) loaded ICG by electrostatic adsorption. The morphology and properties of Fe-Tcpp and Fe-Tcpp@ICG were characterised by ultraviolet-visible absorption spectrometer, X-ray diffraction, thermogravimetric analyzer and transmission electron microscope, respectively. A non-enzymatic photoelectrochemical sensor based on Fe-Tcpp@ICG was constructed to quantitatively detect hydrogen peroxide in tumor microenvironment. Under the optimal conditions, the linear range of detecting hydrogen peroxide was 0.01-50 mmol/L with detection limit of 0.2 μmol/L (S/N = 3). This sensor proposed a simple, fast, sensitive and label-free method for the detection of hydrogen peroxide. Moreover, the results also showed that the Fe-Tcpp@ICG can catalyze the decomposition of hydrogen peroxide to generate singlet oxygen, which can kill tumor cells. These indicated that this material was expected to be used for detecting hydrogen peroxide and inhibition of tumor cell growth.

Bi/BiVO4/NiFe-LDH heterostructures with enhanced photoelectrochemical performance for streptomycin detection

Streptomycin (STR) plays an essential role in bacterial infection treatments. Selectivity and sensitivity of photoelectrochemical (PEC) sensors are the two most important parameters, which can be measured using the photosensitivity of its active material. We prepared a novel PEC sensor to detect STR using Bi/BiVO₄/LDH (layered double hydroxides) heterostructures as an active material, which is photoactive in the visible light wavelength range. The simultaneous presence of LDH and Bi/BiVO₄ enhanced the material photocurrent response, which was linear to the STR concentrations in the 0.01-500 nmol/L range. The STR detection limit by this sensor was 0.0042 nmol/L. Our novel PEC-based sensing strategy includes using an ultra-sensitive and highly selective sensor for STR detection. Additionally, the two-pot synthesis of Bi/BiVO₄/LDH developed in this work is environmentally friendly.

In-situ preparation of CuO nanoparticles decorated In2O3 pn heterojunction composite for the photoelectrochemical detection of ornidazole

The eco-friendly synthesis of metal oxides pn junction composite with high visible light absorption and its photoelectrochemical monitoring on antibiotics is reported. The In₂O₃-CuO pn heterojunction composite was successfully prepared by in-situ hydrothermal decoration of CuO on the prepared In₂O₃ using a simple reflux method. The obtained nanorods like In₂O₃-CuO pn heterojunction exhibited high conductivity with excellent stability for the facilitated photoelectrochemical detection of ornidazole (ONZ) that plays a role in aquatic toxicology. The photo-stability and optical characteristics of the In₂O₃-CuO heterojunction composite were analyzed through photocurrent and UV-visible studies. Mechanism of ONZ signaling has been proposed with appropriate band levels derived by Mott-Schottky analysis. An optimized In₂O₃-CuO heterojunction detects ONZ in the range 0.05-65.3 nM with 0.0092 nM as the limit of detection at - 0.45 V (vs. Ag/AgCl) working potential. The practical applicability of the sensor device was tested in chicken meat, human urine, and lake water samples containing ONZ. The recoveries of real samples were above 95% and results obtained were compared with electrochemical methods.

Molecularly imprinted photoelectrochemical sensor for detecting tetrabromobisphenol A in indoor dust and water

The gradual emissions of tetrabromobisphenol A (TBBPA) from the primitive recycling of E-waste create human health threats, which urgently require to develop an efficient, rapid yet simple detection method. The present study conducts a highly sensitive molecularly imprinted photoelectrochemical sensor (MIPES) containing molecularly imprinted (MI)-TiO₂, Au, and reduced graphene oxide for the trace detection of TBBPA in indoor dust and surface water from an E-waste recycling area. The photocurrent response is used to evaluate the sensing performance of the MIPES toward TBBPA detection. The working potential for amperometry is 0.48 V. The wavelength range for photoelectrochemical detection is 320-780 nm. The sensor shows a detection range of 1.68 to 100 nM with a low limit of detection of 0.51 nM (LOD = 3 s_b/S) and a limit of quantification of 1.68 nM (LOQ = 3.3 LOD). In addition, the MIPES sensor exhibits rapid, excellent reproducibility, selectivity, and long-term stability toward TBBPA detection. The relative standard deviation of three measurements for real samples is less than 7.0%, and the recovery range is 90.0-115%. The surface of molecular imprinting contributes to the high charge separation and sensing photocurrent response of TBBPA, which is confirmed by single-particle photoluminescence spectroscopy. The present study provides a new facile sensor with highly sensitive yet rapid response to detect environmental pollutants in E-waste by using the MIPES.

A highly sensitive photoelectrochemical aptasensor based on BiVO4 nanoparticles-TiO2 nanotubes for detection of PCB72

In this work, a simple and highly sensitive photoelectrochemical (PEC) aptasensor has been developed for detecting PCB72 based on TiO₂ nanotubes (NTs) decorated with BiVO₄ nanoparticles (NPs). The BiVO₄ NPs-TiO₂ NTs composites prepared through a simple hydrothermal method exhibit good visible-light adsorption ability, high PEC response and perfect photo-excited stability. The synthesized composites were explored as the photoactive sensing materials for development of a PEC sensing platform for the first time. Here, Au nanoparticles (NPs) were first deposited the composites, and the anti-PCB72 aptamer molecules were immobilized on the Au NPs-deposited BiVO₄ NPs-TiO₂ NTs. The developed PEC aptasensor exhibits high sensitivity and specificity for PCB72 with a wide linear range from 1 ng/L to 500 ng/L and a low detection limit of 0.23 ng/L. The application of the aptasensor was evaluated by determining PCB 72 in the environment water samples. Thus, a simple and efficient PEC sensing platform was established for detecting the content of PCBs in the environment.

Rational design of built-in stannic oxide-copper manganate microrods p-n heterojunction for photoelectrochemical sensing of tetracycline

Tetracycline (TC), a popularly found drug pollutant, can be contaminated in food and aquatic regions and causes a severe impact on human health. In this research, a visible light active p-stannic oxide/n-copper manganate (p-SnO₂/n-CuMnO₂) heterojunction was synthesized and has been applied for a signal on photoelectrochemical sensing of antibiotic TC. Firstly, the n-SnO₂ microrods were synthesized via a simple and efficient homogeneous precipitation method and the p-CuMnO₂ nanoparticles were synthesized by a facile ultrasound-assisted hydrothermal method. The SnO₂/CuMnO₂ microrods p-n heterojunction was prepared through a simple impregnation method and physicochemical properties of the microrods are characterized by using X-ray diffraction (XRD), Raman, Brunauer-Emmett-Teller (BET), Fourier-transform infrared (FTIR), UV-Vis diffuse reflectance spectroscopy (UVDRS), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and Mott-Schottky analyses. The photoelectrochemical sensing performance of SnO₂/CuMnO₂ microrods was 2.7 times higher than that of as-synthesized pure SnO₂ microrods is due to the more visible light absorption ability and p-n heterojunction (synergy). The designed SnO₂/CuMnO₂/ITO sensor gives photocurrent signals for the detection of TC in the range of 0.01-1000 μM with the detection limit (LOD) of 5.6 nM. The practical applicability of the sensor was monitored in cow milk and the Taipei River water sample.

New application for TiO2 P25 photocatalyst: A case study of photoelectrochemical sensing of nitrite ions

Developing photoelectrochemical (PEC) sensors based on photocatalytic materials has recently attracted great interest as an emerging technology for environmental monitoring. TiO₂ P25 is a well-known highly active photocatalyst, cheap, and produced commercially on a large scale. In the current work, a practical and durable TiO₂-based PEC sensor has been fabricated by immobilizing TiO₂ P25 nanoparticles at disposable screen-printed carbon substrates using drop-casting method. The fabricated PEC sensor has been applied for the anodic-detection and determination of nitrite (NO₂^-) ions under UV(A) light (LED, 365 nm) using chronoamperometry (CA) and differential pulse voltammetry (DPV). Linear calibration curves were obtained between the photocurrent responses and the concentrations of NO₂^- ions in the ranges of 0.1-5.0 and 0.5-10 mg L^-1 for CA and DPV, respectively. Surprisingly, the detection limits (sensitivities) of the fabricated sensor towards NO₂^- ions under light were enhanced by a factor of 4.75 (4.1) and 8.3 (37.4) for CA and DPV, respectively, in comparsion with those measured in the dark. It is found that the photo-excitation of TiO₂ facilitates the photooxidation of NO₂^- ions via the photo-generated holes whereas the photogenerated electrons contribute to the enhanced photocurrent and consequently the enhanced detection limit and sensitivity. The fabricated TiO₂-based PEC sensor exhibits a good stability, durability, and satisfying selectivity for NO₂^- ions determination. These results indicate that the TiO₂-based PEC sensor fabricated by utilizing cheap and commercially available components has great potential for being transferred from lab-to-factory.

Development of a molecularly imprinted photoelectrochemical sensing platform based on NH2-MIL-125(Ti)-TiO2 composite for the sensitive and selective determination of oxtetracycline

In this work, a molecularly imprinted photoelectrochemical (MIP-PEC) sensor based on a novel PEC composite of metal-organic frameworks (MOFs) and TiO₂ (NH₂-MIL-125(Ti)-TiO₂) was established for the ultrasensitive and selective detection of oxytetracycline (OTC). This is the first attempt of applying MOFs in the construction of MIP-PEC sensor. The NH₂-MIL-125(Ti)-TiO₂ was synthesized by a simple one-step solvothermal method and modified onto the surface of indium tin oxide (ITO) electrode as the photosensitive layer. Subsequently, molecularly imprinted polymer (MIP) was modified as recognition element by electropolymerization. The NH₂-MIL-125(Ti)-TiO₂ showed an enhanced photocurrent response due to stronger light absorption capacity and matched energy band. Furthermore, MIP greatly improved the selectivity and sensitivity of the constructed PEC sensor. The photocurrent response of the MIP-PEC sensor was reduced after OTC recognition because the specific binding of OTC to the imprinted cavities blocked the electron transfer of the electrode. Under optimal experimental conditions, the MIP-PEC sensor exhibited a wide detection range from 0.1 nM to 10 μM with a low limit of detection (LOD) of 60 pM, as well as certain reproducibility, stability and good applicability in real samples. The proposed sensor provides ideas for the application of MOFs in the construction of PEC sensors and will offer an alternative method for the detection of other pollutants in the field of food safety.

Oxidized titanium carbide MXene-enabled photoelectrochemical sensor for quantifying synergistic interaction of ascorbic acid based antioxidants system

Antioxidants can protect organization from damage by scavenging of free radicals. When two kinds of antioxidants are consumed together, the total antioxidant capacity might be enhanced via synergistic interactions. Herein, we develop a simple, direct, and effective strategy to quantify the synergistic interaction between ascorbic acid (AA) and other different antioxidants by photoelectrochemical (PEC) technology. MXene Ti₃C₂-TiO₂ composites fabricated via hydrogen peroxide oxidation were applied as sensing material for the antioxidants interaction study. Under excitation of 470 nm wavelength, the photogenerated electrons transfer from the conduction band of TiO₂ nanoparticles to the Ti₃C₂ layers, and the holes in TiO₂ can oxidize antioxidants, leading to an enhanced photocurrent as the detection signal. This PEC sensor exhibits a good linear range to AA concentrations from 12.48 to 521.33 μM as well as obvious antioxidants capability synergism. In particular, the photocurrents of AA + gallic acid (GA) and AA + chlorogenic acid (CHA) mixtures at 476.19 μM increase 1.95 and 2.35 times respectively comparing with the sum of photocurrents of AA and GA or CHA. It is found that the synergistic effect is mainly depending on the fact that AA with the low redox potential (0.246 V vs NHE) can reduce other antioxidants radical to promote regeneration, improving the overall antioxidant performance. Moreover, it is proved that the greater redox potential of antioxidants, the more obvious the synergistic effect. In addition, the sensor was used to real sample assay, which provides available information towards food nutrition analysis, health products design and quality inspection.

A highly-specific photoelectrochemical platform based on carbon nanodots and polymers functionalized organic-inorganic perovskite for cholesterol sensing

Herein, we reported the introduction of carbon nanodots (CNDs) and polyvinylidene fluoride (PVDF) as additives into perovskite CH₃NH₃PbI₃ through in situ synthesis to prepare PVDF-CH₃NH₃PbI₃@CNDs composite, which demonstrated improved water tolerance and mechanical stability. The application of PVDF-CH₃NH₃PbI₃@CNDs for photoelectrochemical sensing was then explored. A molecularly imprinted polymer (MIP) that could specifically recognize cholesterol (CHO) was anchored to PVDF-CH₃NH₃PbI₃@CNDs via a simple thermal polymerization process, followed by elution with hexane. A label-free and sensitive photoelectrochemical method for CHO detection was achieved by using the MIPs@PVDF-CH₃NH₃PbI₃@CNDs platform. The detection limit for CHO was 2.1 × 10^-14 mol/L, lower than most of the existing CHO detection methods. In our perception, this platform can be extended to numerous other analytes. This research result may provide a new understanding to improve the performance and broaden the application range of organic-inorganic perovskites.

An enhanced photoelectrochemical sensor for aflatoxin B1 detection based on organic-inorganic heterojunction nanomaterial: poly(5-formylindole)/NiO

A new strategy for enhancing the photoelectric activity of poly(5-formylindole) (P5FIn) was developed by introducing the inorganic semiconductor material (NiO) to form organic-inorganic heterojunctions. P5FIn/NiO heterojunctions were firstly prepared by combining hydrothermal synthesis and electrochemical polymerization. Due to the synergistic effect between P5FIn and NiO, the photoelectrochemical (PEC) performance of this heterojunction was significantly enhanced compared to pure P5FIn and NiO. The reason for the enhanced PEC performance is mainly attributed to the increased visible light utilization and the bandgap matching effect of the P5FIn/NiO heterojunctions. Based on the prepared P5FIn/NiO heterojunctions, a novel PEC sensor for aflatoxin B1 (AFB1) detection was also constructed with a wide linear range of 0.005-50 ng mL^-1 and a limit of detection (LOD) of 0.0015 ng mL^-1. Moreover, this constructed PEC sensor also had good stability, reproducibility, selectivity, and satisfactory actual sample detection ability. This strategy may inspire more design and application of high-performance photoelectric active material based on inorganic semiconductor and organic conducting polymer heterojunctions. Graphical abstract.

Synergetic Ag2S and ZnS quantum dots as the sensitizer and recognition probe: A visible light-driven photoelectrochemical sensor for the "signal-on" analysis of mercury (II)

A visible-light-driven photoelectrochemical (PEC) sensor has been developed for the "signal-on" analysis of Hg²⁺ by the synergetic combination of low-bandgap Ag₂S and wide-bandgap ZnS quantum dots (QDs). Ag₂S QDs were synthesized with bead-chain-like structure by the self-assembly route and further covalently bound with ZnS QDs to be coated onto the indium tin oxide (ITO) electrodes. It was discovered that the ZnS@Ag₂S-modified electrodes could display the visible-light-driven PEC behavior, of which Ag₂S and ZnS QDs could act as the PEC sensitizer and Hg²⁺-recognition probe, respectively. More importantly, the photocurrent responses of the developed electrodes could be specifically turned on in the presence of Hg²⁺ under the visible-light irradiation, presumably due to that Hg²⁺ might conduct a Zn-to-Hg exchange on ZnS QDs to trigger the formation of HgS/ZnS@Ag₂S heterojunction towards the enhanced electron-hole separation. The as-prepared PEC sensor could facilitate the detection of Hg²⁺ with concentrations ranging from 0.010-1000 nM, with a detection limit of about 1.0 pM. Besides, the feasibility of practical applications of the developed PEC analysis strategy was verified by probing Hg²⁺ in environmental water samples. Such a visible-light-driven PEC detection platform with the unique "turn-on" signal output may promise for the extensive applications for Hg²⁺ evaluation.

Comparison between electrochemical and photoelectrochemical detection of dopamine based on titania-ceria-graphene quantum dots nanocomposite

In this study, titania-ceria-graphene quantum dot (TC-GQD) nanocomposite was synthesized by hydrothermal method for the first time. The prepared nanomaterials were characterized by XRD, FTIR dynamic light scattering (DLS), FESEM, HRTEM, and EDX spectroscopy along with elemental mapping. The synergistic effect of the nanocomposite components was studied by diffuse reflectance spectroscopy (DRS) and electrical conductivity meter. The results showed that band gap of TC-GQD nanocomposite was shifted to visible lights relative to its components (1.3 eV), and electrical conductivity of the sample was significant increased to 89.5 μS cm^-1. After chemical and physical characterization, prepared new nanocomposites were used to design a new electrochemical (EC) and photoelectrochemical (PEC) dopamine (DA) sensors. In both EC and PEC methods effecting experimental parameters were optimized. Due to the synergic effect of the nanocomposite components, an outstanding photocurrent response was observed for DA based on PEC sensor. A linear calibration curve with a lower detection limit of 22 nM DA, and sensitivity of 13.8 mA/mM_(DA), in a wider range of 0.3-750 μM DA, was obtained for TC-GQD/GCE electrode in PEC. While, the TC-GQD/GCE electrode detected DA in the range of 1-500 μM DA, with two linear calibration curve, detection limit of 0.22 μM DA, and sensitivity of 4.9 mA/mM_(DA), in the EC. Observed results from EC and PEC sensors are presented and compared.

Enhanced photoelectrochemical sensing performance of graphitic carbon nitride by nitrogen vacancies engineering

Ciprofloxacin (CIP) as a typical antibiotic is widely used to produce antimicrobial drugs. Determination of CIP has raised extensive concern due to its possible toxic effects on human health. Here, a simple photoelectrochemical (PEC) sensor for detecting CIP has been developed by using the nitrogen-deficient graphitic carbon nitride (ND-g-CN) as a PEC active material. The ND-g-CN material exhibits two-dimension (2D) thin sheet structure with abundant nitrogen vacancies. The 2D thin sheet structure can enable the effective charge separation and transfer, thus dramatically improving the PEC performance. Simultaneously, nitrogen vacancies can serve as charge trap to efficiently inhibit the charge recombination. Furthermore, the synergistic effect of the two can widen the absorption edge and decrease the band gap of ND-g-CN material, resulting in increasing light harvesting and enhancing PEC performance. CIP can be oxidized by the holes of ND-g-CN, thus realizing effective charge separation, which can result in the amplification of the photocurrent. The designed PEC sensor demonstrated a wide detection range from 60 to 19090 ng L^-1 and a low detection limit of 20 ng L^-1 for CIP assay. This strategy broadens the application of graphitic carbon nitride (g-CN) material in PEC field and presents a promising potential for the practical application in the environmental monitoring.

A molecularly imprinted photoelectrochemical sensor based on the use of Bi2S3 for sensitive determination of dioctyl phthalate

A molecularly imprinted polymer photoelectrochemical (MIP-PEC) sensor based on bismuth sulfide (Bi₂S₃) is described for the determination of the plasticizer dioctyl phthalate (DOP). Bi₂S₃ was used as the photoelectrical converter of the sensor, and visible light was utilized as the excitation source. The molecular imprinting film was prepared through the electropolymerization of monomers in the presence of DOP. Under optimal experimental conditions, the photoelectrochemical response was linearly proportional to the logarithm of the DOP concentration in the 0.5-70 pM DOP concentration range, and the detection limit was 0.1 pM. The method is highly stable and reproducible. It was applied to the determination of DOP in spiked water samples. Graphical abstract A novel molecularly imprinted photoelectrochemical sensor with high sensitivity and high selectivity based on Bi₂S₃ was developed for dioctyl phthalate detection. Bi₂S₃ was firstly used as a photoelectric converter in photoelectrochemical sensor to improve the sensitivity of the sensor. Combining photocurrent measurement with molecular imprinting technique makes the sensor highly selective.

A novel photoelectrochemical strategy based on an integrative photoactive heterojunction nanomaterial and a redox cycling amplification system for ultrasensitive determination of microRNA in cells

An ultrasensitive photoelectrochemical (PEC) bioassay for determination of microRNA was proposed based on an integrative photoactive heterojunction nanomaterial to provide the basis of excellent PEC responses and an efficient redox cycling amplification system to improve the detection performances. To establish the bioassay system, the biosensor was firstly modified with Bi₂WO₆@Bi₂S₃ and alkaline phosphatase (ALP). The detection solution was composed of ascorbic acid phosphate (AAP) and ferrocenecarboxylic acid (FcA), where ALP converted AAP into ascorbic acid (AA) to trigger a process of redox cycling amplification by reducing FcA⁺ to FcA, resulting in enhanced photocurrent responses of Bi₂WO₆@Bi₂S₃. In the presence of microRNA 21, it could trigger a hybridization chain reaction via the special designed hairpin DNA to produce a long repeated DNA sequences to inhibit ALP activity. Thus the reduced ALP activity and consequently decreased photocurrent signal could be obtained for detection of microRNA 21. As expected, this bioassay system performed the satisfactory performances for the ultrasensitive detection of microRNA 21 in the range from 1 fM to 1 nM with an experimental detection limit of 0.26 fM and acceptable practical applicability. Collectively, an efficient PEC bioassay for microRNA 21 is established and this strategy can be expanded to detect other microRNAs, even other molecules in cells.

Ti3C2/Cu2O heterostructure based signal-off photoelectrochemical sensor for high sensitivity detection of glucose

Photoelectrochemical (PEC) sensing has emerged as a simple and practical method for the analysis and detection, its separated optical signal and detection electrical signal give it the advantages of reduced background noise and outstanding sensitivity. Here, we synthesized a Ti₃C₂/Cu₂O composite through simple oil bath heating process, whose excellent PEC performance and sensitive photoelectric response to glucose make it a propitious substitution to glucose oxidase. On this basis, we construct a PEC non-enzymatic sensor based on the Ti₃C₂/Cu₂O heterostructure for the detection of glucose. Under the optimal conditions, the photocurrent of Ti₃C₂/Cu₂O is linear with the logarithm value of glucose concentration in the wide range of 0.5 nM to 0.5 mM with a detection limit of 0.17 nM. Furthermore, the successful detection of glucose in standard samples and human serum by the proposed Ti₃C₂/Cu₂O based PEC non-enzymatic sensor demonstrates the application prospect of heterostructure material in PEC sensor, which provides a new thought for the design and construction of PEC non-enzymatic sensing platform.

Tremella-like ZnIn2S4/graphene composite based photoelectrochemical sensor for sensitive detection of dopamine

Tremella-like ZnIn₂S₄ (ZISt) and flower-like microsphere ZnIn₂S₄ (ZISm) were synthesized via a straightforward hydrothermal method. It was found that the ZISt was superior to ZISm for photoelectrochemical (PEC) sensing because of its large surface area and high photocatalytic activity. A composite of ZISt and graphene (GR) was prepared and used for the PEC sensing of dopamine (DA). Here DA acted as an electron donor to scavenge the hole and inhibit the charge recombination. The GR enhanced visible light absorption and accelerated electron transfer, amplifying the photocurrent signal. The strong chelating coordination interaction between DA and Zn(II) in ZISt guaranteed the selective adsorption of target analyte. Thus the resulting ZISt/GR photoelectrode showed sensitive and selective PEC response to DA. Under the optimized conditions, the linear response range was from 0.01 to 20 μM, and the detection limit was down to 0.001 μM. Additionally, the sensor had good stability and reproducibility, and it could be used for the detection of DA in real samples.