One-Pot Synthesis of N-Graphene Quantum Dot-Functionalized I-BiOCl Z-Scheme Cathodic Materials for "Signal-Off" Photoelectrochemical Sensing of Chlorpyrifos

Ultrasensitive Paper-Based Photoelectrochemical Biosensor for Acetamiprid Detection Enabled by Spin-State Manipulation and Polarity-Switching

Efficient carrier separation is vitally crucial to improving the detection sensitivity of photoelectrochemical (PEC) biosensors. Here, we developed a facile strategy to efficiently regulate the carrier separation efficiency of the photoactive matrix BiOI and In2S3 signal label functionalized paper chip by manipulation of electrons spin-state and rational design of electron transport pathways. The spin-dependent electronic structures of BiOI and In2S3 were regulated via enhanced electron-spin parallel alignment induced by an external magnetic field, markedly retarding carrier recombination and extending their lifetime. Simultaneously, with the progress of the target-induced catalytic hairpin assembly process, the transfer path of photogenerated carriers was changed, leading to a switch in photocurrent polarity from cathode to anode. This reversed electron transport pathway not only boosted the separation ability of photogenerated electrons but also eliminated false-positive and false-negative signals, thereby further improving the detection sensitivity. As a proof of concept, the well-designed magnetic field-stimulated paper-based PEC biosensor showed highly selectivity and sensitivity for acetamiprid assay with a wide linear range of 1 fM to 20 nM and an ultralow detection limit of 0.73 fM. This work develops a universal strategy for improving the sensitivity of biosensors and exhibits enormous potential in the fields of bioanalysis and clinical diagnosis.

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.

Graphene-based functional electrochemical sensors for the detection of chlorpyrifos in water and food samples: a review

Prolonged and excessive use of chlorpyrifos (CPS) has caused severe pollution, particularly in crops, vegetables, fruits, and water sources. As a result, CPS is detected in various food and water samples using conventional methods. However, its applications are limited due to size, portability, cost, etc. In this regard, electrochemical sensors are preferred for CPS detection due to their high sensitivity, reliability, rapid, on-site detection, and user-friendly. Notably, graphene-based electrochemical sensors have gained more attention due to their unique physiochemical and electrochemical properties. It shows high sensitivity, selectivity, and quick response because of its high surface area and high conductivity. In this review, we have discussed an overview of three graphene-based different functional electrochemical sensors such as electroanalytical sensors, bio-electrochemical sensors, and photoelectrochemical sensors used to detect CPS in food and water samples. Furthermore, the fabrication and operation of these electrochemical sensors using various materials (low band gap material, nanomaterials, enzymes, antibodies, DNA, aptamers, and so on) and electrochemical techniques (CV, DPV, EIS, SWV etc.) are discussed. The study found that the electrical signal was reduced with increasing CPS concentration. This is due to the blocking of active sites, reduced redox reaction, impedance, irreversible reactions, etc. In addition, acetylcholinesterase-coupled sensors are more sensitive and stable than others. Also, it can be further improved by fabricating with low band gap nanomaterials. Despite their advantages, these sensors have significant drawbacks, such as low reusability, repeatability, stability, and high cost. Therefore, further research is required to overcome such limitations.

Photocurrent-polarity switching between methylene blue-loaded liposome and iodine-doped BiOCl for in-situ amplified immunoassay

This work designed a liposome-mediated photocurrent polarity switching immunosensor depending on the reversed photocurrent of iodine-doped BiOCl (I-BOC) nanoflowers induced by the released methylene blue (MB) for the detection of prostate-specific antigen (PSA). Initially, MB-loaded liposomes as indicators were confined within the microplates to participate in the sandwiched immunoreaction and lysed under the treatment of Triton X-100 to release numerous MB. Owing to the host-guest recognition between β-cyclodextrin (β-CD) and MB, the released MB was immobilized on the β-CD-modified I-BOC/FTO electrode and triggered the photocurrent polarity reversal from cathodic photocurrent to anodic photocurrent. The sensing platform realized an accurate and sensitive assay of PSA due to the effective elimination of false-positive/negative signals in a linear range of 0.02-50 ng mL-1 with a limit of detection of 12 pg mL-1. Furthermore, this work not only conjugated liposome-assisted signal amplification strategy with the photocurrent polarity switching system but also provided a novel pathway for various protein determinations.

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

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

Signal Modulation of Organic Photoelectrochemical Transistor by a Z-Scheme Photocathodic Gate: An Innovative Dual Amplification Strategy for Sensitive Aptasensing Application

Pursuing a more efficient signal amplification strategy is highly demanded for improving the performance of the promising cathodic photoelectrochemical (PEC) sensors. In this work, we present an extremely effective dual signal amplification strategy by the integration of a Z-scheme nanohybrids-based photocathode with the effective signal modulation of an organic photoelectrochemical transistor (OPECT) device. Specifically, photocathodic gate material of CdTe-BiOBr nanohybrids with a Z-scheme electron-transfer route was designed and synthesized for preliminary improvement of the activity of the photogate; afterward, signal modulation of the OPECT system by the photocathodic gate of CdTe-BiOBr was then accomplished for further signal amplification by 2 orders of magnitude. As a result, the output PEC signal of CdTe-BiOBr was enhanced by 17.5-fold as compared to BiOBr, and the channel current (IDS) of the OPECT device was 117-fold magnified than its gate current (IG) response. Exemplified by tetracycline (TC) as a model target and aptamer as the specific recognition element, a versatile cathodic aptasensing platform was constructed based on the proposed OPECT device. The introduced OPECT aptasensor merits advantages, including a good linear range (1.0 × 10-12 to 1.0 × 10-6 M), a low limit of detection (4.2 × 10-13 M), and superior sensitivity than the traditional PEC methods for TC detection, which represents a universal protocol for developing the innovative photocathodic OPECT sensing platform toward accurate analysis.

Photocurrent Polarity Reversal Induced by Electron-Donor Release for the Highly Sensitive Photoelectrochemical Detection of Vascular Endothelial Growth Factor 165

Photocurrent polarity reversal is a switching process between the anodic and cathodic pathways and is critical for eliminating false positivity and improving detection sensitivity in photoelectrochemical (PEC) sensing. In this study, we construct a PEC sensor with excellent photocurrent polarity reversal induced by ascorbic acid (AA) as an electron donor with the energy level matching the photoactive material zirconium metal-organic framework (ZrMOF). The ZrMOF-modified electrode demonstrates cathodic photocurrent in the presence of O2 as an electron acceptor, while the anodic photocurrent is generated in the presence of AA, achieving photocurrent polarity reversal. By the in situ release of AA from AA-encapsulated apoferritin modified with DNA 2 (AA@APO-S2) as a detection tag in the presence of trypsin after the recognition of hairpin DNA-modified indium tin oxide to the reaction product of aptamer/DNA 1 with the target protein and the following rolling cycle amplification for introducing the detection tag to the sensing interface, the reversed photocurrent shows an enhanced photocurrent response to the target protein, leading to a highly sensitive PEC sensing strategy. This strategy realizes the detection of vascular endothelial growth factor 165 with good specificity, a wide linear range, and a low detection limit down to 5.3 fM. The actual sample analysis offers the detection results of the proposed PEC sensor comparable to those of commercial enzyme-linked immunosorbent assay tests, indicating the promising application of the photocurrent polarity reversal-based PEC sensing strategy in biomolecule detection and clinical diagnosis.

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.

Combined Gadolinium and Boron Neutron Capture Therapies for Eradication of Head-and-Neck Tumor Using Gd10B6 Nanoparticles under MRI/CT Image Guidance

Eradication of head-and-neck (H&N) tumors is very difficult and challenging because of the characteristic feature of frequent recurrence and the difficulty in killing cancer stem cells. Neutron capture therapy (NCT) is emerging as a noninvasive potential modality for treatments of various types of tumors. Herein, we report that 98.5% 10B-enriched anti-EGFR-Gd10B6 nanoparticles can not only deliver large doses of 158 μg 10B/g tumor tissues as well as 56.8 μg 157Gd/g tumor tissues with a very high tumor-to-blood (T/B) 10B ratio of 4.18, but also exert very effective CT/MRI image-guided combined GdBNCT effects on killing cancer stem cells and eradication of recurrent head-and-neck (H&N) tumors. This leads to a long average half-lifespan of 81 days for H&N tumor-bearing mice, which is a record-making result, and surpasses the best result reported in the literature using combined radiotherapy and T cell-mediated immunotherapy (70 d).

Self-Cleaning Recyclable Multiplexed Photoelectrochemical Sensing Strategy Based on Exonuclease III-Assisted Signal Discrimination

For discriminating the signals of multi-targets, multiplexed photoelectrochemical (PEC) detection is generally accomplished by modulating the light source or voltage, which prospect is usually limited by expensive instrumentation, tedious operational steps, and time-consuming material screening. To realize multiplexed determination on single photoelectric interface using the routine technique, a non-instrument-assisted strategy for signal discrimination needs to be explored. Herein, we propose an exonuclease III-mediated multiple PEC signals resolution strategy and construct a self-cleaning recyclable multiplexed PEC sensor using a porphyrin-bipyridine-based covalent organic framework (Por-Bpy COF) photocathode. Specifically, following the dual-target recognition event, exonuclease III cleaves the DNA strand attached to the magnetic bead so that the two signal labels can be separated. Once the signal label binds to the DNA on the electrode surface (E-DNA), exonuclease III turns to excise the DNA strand of the signal label and consequently the E-DNA can repeatedly bind different signal labels. As a result, distinguishable photocurrent signals of different targets can be generated on a single photoelectric interface. The feasibility of this multiplexed sensor is verified by detecting two coexisting mycotoxins aflatoxin B1 and zearalenone. On account of eliminating the instrumentation constraints and simplifying the experimental procedures, the proposed sensing strategy may provide a brand-new idea for the exploration of portable multiplexed PEC sensing devices.

Fabricating BiOCl/BiVO4 nanosheets wrapped in a graphene oxide heterojunction composite for detection of an antihistamine in biological samples

Antibiotics are essential medications for human and animal health, as they are used to battle urinary infections and bacterial diseases. Therefore, the rapid determination of antibiotic drugs in biological samples is necessary to address the current clinical challenge. Here, we developed a heterojunction ternary composite of BiOCl/BiVO₄ nanosheets enriched with graphene oxide (BiOCl/BiVO₄@GO) for accurate and minimal-level detection of an antihistamine (promethazine hydrochloride, PMZ) in urine samples. The BiOCl/BiVO₄ nanosheets were prepared by a wet chemical approach using a deep eutectic green solvent. The spectroscopic and analytical methods verified the formation and interaction of the BiOCl/BiVO₄@GO composite. Our results showed that the thoroughly exfoliated BiOCl/BiVO₄@GO composite retained good electrical conductivity and fast charge transfer toward the electrode-electrolyte interface in neutral aqueous media. In addition, the experimental conditions were accurately optimized, and the BiOCl/BiVO₄@GO composite showed excellent electrocatalytic activity toward the oxidation of PMZ. Indeed, the BiOCl/BiVO₄@GO composite demonstrated a good linear response range (0.01-124.7 μM) and a detection level of 3.3 nM with a sensitivity of 1.586 μA μM^-1 cm^-2. In addition, the BiOCl/BiVO₄@GO composite had excellent storage stability, good reproducibility, and reliable selectivity. Finally, the BiOCl/BiVO₄@GO displayed a desirable recovery level of PMZ in urine samples for real-time monitoring.

Selenylation to charge transfer improvement at the counter electrode (CE)/electrolyte interface for nanocrystalline Cu1.8S1-xSex CEs

Pt counter electrodes (CEs) have been widely used in dye-sensitized solar cells (DSSCs) due to their high conductivity and electrocatalytic activity. However, industrialization of DSSCs is limited by shortcomings of Pt CEs such as being expensive, and weak corrosion resistance in electrolytes. Reported in this paper is two simple approaches to Pt-free Cu_1.8S_1-xSe_x CEs. Nanocrystalline Cu_1.8S_1-xSe_x CEs were fabricated via two processes, that is, a solvothermal process to Cu_1.8S_1-xSe_x powder followed by CE fabrication, and a solvothermal process and CE fabrication to Cu_1.8S films followed by selenylation to Cu_1.8S_1-xSe_x CEs. Photoelectric conversion efficiencies (PCE) of 4.02% and 4.16% were achieved respectively by the as-fabricated Cu_1.8S_1-xSe_x CEs. Compared with the cells with Cu_1.8S CEs fabricated by the same processes, increases of 19% and 45% were achieved, respectively. The PCE improvement comes from the enhancement of charge transfer at the CE/electrolyte interface induced by the selenylation of the CEs.

Recent advances in electrochemical and optical sensing of the organophosphate chlorpyrifos: a review

Chlorpyrifos (CP) is one of the most popular organophosphorus pesticides that is commonly used in agricultural and nonagricultural environments to combat pests. However, several concerns regarding contamination due to the unmitigated use of chlorpyrifos have come up over recent years. This has popularized research on various techniques for chlorpyrifos detection. Since conventional methods do not enable smooth detection, the recent trends of chlorpyrifos detection have shifted toward electrochemical and optical sensing techniques that offer higher sensitivity and selectivity. The objective of this review is to provide a brief overview of some of the important and innovative contributions in the field of electrochemical and optical sensing of chlorpyrifos with a primary focus on the comparative advantages and shortcomings of these techniques. This review paper will help to offer better perspectives for research in organophosphorus pesticide detection in the future.

Organic-Inorganic Hybrid Flower-Shaped Microspheres Applied in Photoelectrochemical Sensing

Organic-inorganic hybrid materials are rarely applied in photoelectrochemical (PEC) sensing because of the serious charge-carrier recombination in organic conjugated polymers. In this work, a series of poly(3,4-ethylenedioxythiophene) (PEDOT)/ZnIn2S4 hybrid flower-shaped microspheres were synthesized using ionic liquids (ILs) as the supporting electrolyte for EDOT electropolymerization and as the regulating reagent for controlling ZnIn2S4 growth, respectively. It was found that the hybrid material [HOEMIM]NTf2-PEDOT/[HOEMIM]BF4-ZnIn2S4 ([HOEMIM]+: 1-hydroxyethyl-3-methylimidazolium cation; NTf2-: bis(trifluoromethanesulfonyl)amide) was the optimal one, with a smooth, transparent, and continuous polymer film covering the uniform and ordered cross-linked nanosheet arrays. The hybrid material could produce a high anodic photocurrent, which was about 78 times as high as that produced by the [HOEMIM]BF4-ZnIn2S4. The enhancement effect should be the highest among all the organic-inorganic hybrid materials reported so far. This was related to its unique micromorphology structure, p-n heterojunction, and the coexisting ILs, which restrained the charge-carrier recombination in PEDOT and enhanced PEDOT sensitization to ZnIn2S4. Then, a carcinoembryonic antigen PEC immunosensor was constructed based on the photoanodic sensing platform, and it exhibited good performance. Furthermore, the [HOEMIM]BF4-ZnIn2S4 was treated with NaClO solution to create the [HOEMIM]NTf2-PEDOT/[HOEMIM]BF4-S-ZnwInxSyOz general platform for both photoanodic and photocathodic sensing. As a proof of concept, L-cysteine and dissolved oxygen were used as models for photoanodic and photocathodic sensing, respectively. The results demonstrated that the general PEC platform was quite competent. This work opens up a window for the design of organic-inorganic hybrid PEC materials and will promote the application of such hybrid materials in PEC biosensing.

Bismuth Oxychloride Nanomaterials Fighting for Human Health: From Photodegradation to Biomedical Applications

Environmental pollution and various diseases seriously affect the health of human beings. Photocatalytic nanomaterials (NMs) have been used for degrading pollution for a long time. However, the biomedical applications of photocatalytic NMs have only recently been investigated. As a typical photocatalytic NM, bismuth oxychloride (BiOCl) exhibits excellent photocatalytic performance due to its unique layered structure, electronic properties, optical properties, good photocatalytic activity, and stability. Some environmental pollutants, such as volatile organic compounds, antibiotics and their derivatives, heavy metal ions, pesticides, and microorganisms, could not only be detected but also be degraded by BiOCl-based NMs due to their excellent photocatalytic and photoelectrochemical properties. In particular, BiOCl-based NMs have been used as theranostic platforms because of their CT and photoacoustic imaging abilities, as well as photodynamic and photothermal performances. However, some reviews have only profiled the applications of dye degradation, hydrogen or oxygen production, carbon dioxide reduction, or nitrogen fixation of BiOCl NMs. There is a notable knowledge gap regarding the systematic study of the relationship between BiOCl NMs and human health, especially the biomedical applications of BiOCl-based NMs. As a result, in this review, the recent progress of BiOCl-based photocatalytic degradation and biomedical applications are summarized, and the improvement of BiOCl-based NMs in environmental and healthcare fields are also discussed. Finally, a few insights into the current status and future perspectives of BiOCl-based NMs are given.

Highly sensitive and selective photoelectrochemical aptasensing of di-2-ethylhexyl phthalate based on graphene quantum dots decorated TiO2 nanotube arrays

A photoelectrochemical (PEC) sensing platform for di-2-ethylhexyl phthalate (DEHP) was constructed using graphene quantum dots decorated TiO₂ nanotube arrays (GQDs-decorated TiO₂ NTs) as the transducer species and the anti-DEHP aptamer as the biological recognition element. GQDs were synthesized using the alkali-mediated hydrothermal method, and then anchored onto the TiO₂ NTs uniformly and intimately via pronounced electrostatic interaction. Coupling GQDs with TiO₂ NTs not only enhanced visible-light absorption, but promoted charge separation and transportation, exhibiting excellent photocurrent response, and PEC activity. Various means were conducted to explore morphologies, optical, structural and PEC properties of the materials. As an identification unit, the anti-DEHP aptamer molecules were immobilized on GQDs-decorated TiO₂ NTs using a cross-linking coupling method. The developed PEC sensing platform exhibits excellent sensing behavior for DEHP, and provides a low detection limit of 0.1 ng/L, high selectivity and stability. Meanwhile, its application in real environmental samples was evaluated and satisfying results were achieved. Thus, the established sensing platform provides a promising tool to detect DEHP in the environment.

Advances in preparation, mechanism and applications of graphene quantum dots/semiconductor composite photocatalysts: A review

Due to the low efficiency of single-component nano materials, there are more and more studies on high-efficiency composites. As zero dimensional (0D) non-metallic semiconductor material, the emergence of graphene quantum dots (GQDs) overcomes the shortcomings of traditional photocatalysts (rapid rate of electron-hole recombination and narrow range of optical response). Their uniqueness is that they can combine the advantages of quantum dots (rich functional groups at edge) and sp² carbon materials (large specific surface area). The inherent inert carbon stabilizes chemical and physical properties, and brings new breakthroughs to the development of benchmark photocatalysts. The photocatalytic efficiency of GQDs composite with semiconductor materials (SCs) can be improved by the following three points: (1) accelerating charge transfer, (2) extending light absorption range, (3) increasing active sites. The methods of preparation (bottom-up and top-down), types of heterojunctions, mechanisms of photocatalysis, and applications of GQDs/SCs (wastewater treatment, energy storage, gas sensing, UV detection, antibiosis and biomedicine) are comprehensively discussed. And it is hoped that this review can provide some guidance for the future research on of GQDs/SCs on photocatalysis.

Black phosphorous quantum dots for signal-on cathodic photoelectrochemical aptasensor monoitoring amyloid β peptide

In this paper, a quantitative cathodic photoelectrochemical aptasensor is described by using black phosphorous quantum dots (BPQDs) as photoactive material and assisted by heme as electron acceptor for sensing of amyloid β peptide (Aβ). Specifically, BPQDs were synthesized by solvothermal method and characterized by various techniques. The as-prepared BPQDs were assembled on the transparent indium tin oxide electrode, and the positively charged poly-l-lysine (PLL) was then absorbed onto BPQDs via electronic interaction. Subsequently, the aptamer as the specific recognition element for Aβ oligomer was introduced on the BPQDs-PLL modified electrode. After bound with heme to form Aβ-heme complex, Aβ oligomer was simultaneously captured by the aptamer on the electrode, resulting in an enhanced photocurrent response. Under the optimized conditions, the present PEC sensor reveals a good linear response to Aβ peptide ranging from 1.0 fM to 100 nM with a detection limit of 0.87 fM. The present signal-on cathodic PEC bioassay possesses the potential to create a new paradigm in amplified PEC assays that could provide outstanding performance for bioanalysis.

Ultrasensitive Double-Channel Microfluidic Biosensor-Based Cathodic Photo-electrochemical Analysis via Signal Amplification of SOD-Au@PANI for Cardiac Troponin I Detection

Interesting double-channel microfluidic chip integration with a sandwich-type cathodic photo-electrochemical (PEC) biosensor is utilized for ultrasensitive and efficient detection of cardiac troponin I (cTnI) based on a signal amplification strategy. The Pd nanoparticles loading on the I-doped bismuth oxybromide with oxygen vacancies (Pd/I:BiOBr-OVs) as a sensing platform can effectively enhance cathodic photocurrent response by improving the visible light absorption ability with I doping, facilitating the efficiency separation of photogenerated electron-hole pairs with OVs, and increasing the electron-transfer rate with Pd loading, where the photogenerated electron could be captured by dissolved O₂ to boost generation of a superoxide anion radical (^•O₂^-). To further enhance the PEC response, a novel superoxide dismutase loaded on gold@polyaniline (SOD-Au@PANI) as a signal amplification label is developed for incubating the detection antibody (dAb). It is particularly noteworthy that SOD can effectively catalyze dismutation of the ^•O₂^- to produce H₂O₂ and O₂, and Au@PANI with a good reduction and catalytic property can catalyze the produced H₂O₂ into H₂O and O₂. Then, the produced O₂ that has been dissolved or adsorbed can capture more photogenerated electrons, resulting in more electron-hole pairs to separate, so as to the cathodic photocurrent signal of this system which can be amplified more significantly. Therefore, a signal amplification cathodic PEC biosensor is prepared for sensitively detecting cTnI, in which a good linearity ranging from 0.1 pg/mL to 100 ng/mL with a low detection limit of 0.042 pg/mL is obtained. Furthermore, the proposed biosensor exhibits excellent sensitivity and high selectivity, which could be extended to detect other disease markers in biological analysis and early disease diagnosis.

Multifunctional CuO/Cu2O Truncated Nanocubes as Trimodal Image-Guided Near-Infrared-III Photothermal Agents to Combat Multi-Drug-Resistant Lung Carcinoma

Despite the development of various therapeutic modalities to tackle cancer, multidrug resistance (MDR) and incomplete destruction of deep tissue-buried tumors remain as long-standing challenges responsible for tumor recurrence and low survival rates. In addition to the MDR and deep tissue photoactivation problems, most primary tumors metastasize to the lungs and lymph nodes to form secondary tumors. Therefore, it leaves a great challenge to develop theranostic approaches to combat both MDR and deep tissue photoactivation problems. Herein, we develop a versatile plasmonic CuO/Cu₂O truncated nanocube-based theranostic nanomedicine to act as a triple modal near-infrared fluorescence (NIRF) imaging agent in the biological window II (1000-1500 nm)/photoacoustic imaging (PAI)/T₁-weighted magnetic resonance (MR) imaging agents, sensitize the formation of singlet oxygen (¹O₂) to exert nanomaterial-mediated photodynamic therapeutic (NIR-II NmPDT), and absorb long NIR light (i.e., 1550 nm) in the biological window III (1500-1700 nm) to exert nanomaterial-mediated photothermal therapeutic (NIR-III NmPTT) effects for the effective destruction of multi-drug-resistant lung tumors. We found that H69AR lung cancer cells do not create drug resistance toward plasmonic CuO/Cu₂O TNCs-based nanomedicines.

Non-noble metal plasmonic enhanced photoelectrochemical sensing of chlorpyrifos based on 1D TiO2-x/3D nitrogen-doped graphene hydrogel heterostructure

Low-cost and resource-rich non-noble metal plasmonic materials have attracted tremendous attention as potential substitutes for plasmonic noble metals. Herein, 3D nitrogen-doped graphene hydrogels (NGH) decorated with Ti³⁺ self-doped 1D rod-shaped titanium dioxide nanorods (TiO_2-x NR), 10-25 nm in size, were prepared by a facile one-step method. It was found that the as-fabricated TiO_2-x NR/NGH showed a synergistic effect, displaying enhanced photoelectrochemical (PEC) activity by controlling the nanoscale architecture and improving the electronic properties, while also producing abundant oxygen vacancies, which extended the light harvesting and suppressed the recombination of electron-hole pairs induced by the non-noble metal surface plasmon resonance (SPR) effect. In particular, the transient-state photocurrent intensity of the TiO_2-x NR/NGH composites was 5.1 times as high as that of pure TiO₂. Therefore, the TiO_2-x NR/NGH composites could serve as a substrate material for PEC sensing, providing a good basis for selective and sensitive detection of chlorpyrifos. Under optimal conditions, the constructed PEC sensor was found to have several advantages including a broad linear range (0.05 ng/mL-0.5 μg/mL), low detection limit (0.017 ng/mL), and considerable stability, demonstrating that the sensor may offer a promising route in the field of environmental analysis.

Construction of 3D Bi/ZnSnO3 hollow microspheres for label-free highly selective photoelectrochemical recognition of norepinephrine

Herein, we reported a label-free and reliable photoelectrochemical (PEC) platform for highly selective monitoring of norepinephrine (NE) based on metallic Bi nanoparticles anchored on hollow porous ZnSnO3 microspheres (3D Bi/ZnSnO3) via a simple solvothermal strategy. The designed 3D Bi/ZnSnO3 Schottky junction exhibited a unique photoanodic response toward NE among other catechol derivatives, such as epinephrine (EP) and dopamine (DA), and effectively shielded the interference from thirteen coexisting biomolecules like uric acid (UA) and ascorbic acid (AA). High selectivity and excellent sensitivity could be correlated to the unique chelating coordination interaction between NE and Zn2+ at surface sites as well as the efficient carrier separation of Bi/ZnSnO3, thereby developing a novel "signal-on" label-free and selective strategy for NE detection. The proposed Bi/ZnSnO3-based PEC sensor achieved remarkable NE biosensing with a low detection limit of 0.68 nmol L-1 and a wide response ranging from 0.002 to 350.0 μmol L-1. The applicability of this biosensor was realized for the selective analysis of NE in human serum, human urine and injection samples, laying the foundation for the label-free PEC monitoring of NE in biological fluids.

Crystal Violet-Sensitized Direct Z-Scheme Heterojunction Coupled with a G-Wire Superstructure for Photoelectrochemical Sensing of Uracil-DNA Glycosylase

Dye sensitization achieving photoelectrochemical (PEC) signal amplification for ultrasensitive bioanalysis has undergone a major breakthrough. In this proposal, an innovative PEC sensing platform is developed by combining Z-scheme WO₃@SnS₂ photoactive materials and a G-wire superstructure as well as a dye sensitization enhancement strategy. The newly synthesized WO₃@SnS₂ heterojunction with outstanding PEC performance is employed as a photoelectrode matrix. Due to the formation of the Z-scheme heterojunction between WO₃ and SnS₂, the migration dynamics of the photogenerated carrier is evidently augmented. To improve sensitivity, the target excision-driven dual-cycle signal amplification strategy is introduced to output exponential c-myc fragments. Crystal violet is then conjugated into the G-quadruplex to amplify the PEC signal, where crystal violet generates excited electrons by capturing visible light and rapidly injects electrons into the conduction band of SnS₂, suppressing the recombination of the photo-induced carrier. Moreover, the G-wire superstructure acts as a universal amplification pathway, ensuring adequate crystal violet loads. Specifically, the biosensor for uracil-DNA glycosylase quantification displays a wide detection range (0.0005-1.0 U/mL) and a lower detection limit (0.00025 U/mL). Furthermore, the Z-scheme electron migration mechanism and the crystal violet sensitization effect are discussed in detail. The construction of the PEC sensor provides a new consideration for signal amplification and material design.

A hollow visible-light-responsive surface molecularly imprinted polymer for the detection of chlorpyrifos in vegetables and fruits

A visible-light-responsive azobenzene derivative, 3,5-dichloro-4-((2,6-dichloro-4-(methacryloyloxy)phenyl)diazenyl)benzoic acid, was synthesized and used as the functional monomer to fabricate a visible-light-responsive core-shell structured surface molecularly imprinted polymer (PS-co-PMAA@VSMIP). After removal of the sacrificial PS-co-PMAA core, a hollow structured surface molecularly imprinted polymer (HVSMIP) was obtained. Both the PS-co-PMAA@VSMIP and HVSMIP were used for the detection of chlorpyrifos, a moderately toxic organophosphate pesticide. They exhibited good visible-light-responsive properties (550 nm for trans→cis and 440 nm for cis→trans isomerization for an azobenzene chromophore) in ethanol/water (9:1, v/v). Compared with the PS-co-PMAA@VSMIP, the HVSMIP had a larger surface area, pore volume, binding capacity, imprinting effect, maximum chemical binding capacity, dissociation constant, and photo-isomerization rate. The HVSMIP was applied to detect trace chlorpyrifos in fruit and vegetable samples. This was achieved by measuring the trans→cis rate constant of the HVSMIP in the sample solution, with good recoveries, low relative standard deviations, and a low detection limit.

Molecularly imprinted photoelectrochemical sensing based on ZnO/polypyrrole nanocomposites for acrylamide detection

A highly sensitive quenching molecular imprinting (MIP) photoelectrochemical (PEC) sensor was proposed to detect acrylamide (AM) by using the photoactive composite of ZnO and polypyrrole (PPy) as the PEC signal probe. ZnO, with high electron mobility, excellent chemical and thermal stability as well as good biocompatibility, was selected as the photoelectrically active material. A polypyrrole film was formed on the nanodisk ZnO by electrochemical polymerization, and the recognition site of AM was left on the surface of the PPy film by elution, enabling the specific detection of AM. The transfer of electrons will be hindered when AM is adsorbed on the ZnO/PPy nanocomposites surface, which results in the decrease of photocurrent signal. The proposed molecularly imprinted PEC sensor exhibits significant detection performance of AM in the range of 10-1 M-2.5 × 10-9 M with a LOD of 2.147 × 10-9 M (S/N = 3). The use of photoelectrochemical technology combined with molecular imprinting technology enables the PEC sensor to have excellent selectivity, superior repeatability, preferable stability, low cost, and easy construction, providing a new method for the detection of AM. The high recovery rate in the detection of real samples of potato chips and biscuits indicates that the proposed PEC sensor has potential in monitoring the emerging food safety risks.

A Mini Review on Bismuth-Based Z-Scheme Photocatalysts

Recently, the bismuth-based (Bi-based) Z-scheme photocatalysts have been paid great attention due to their good solar energy utilization capacity, the high separation rate of their photogenerated hole-electron pairs, and strong redox ability. They are considerably more promising materials than single semiconductors for alleviating the energy crisis and environmental deterioration by efficiently utilizing sunlight to motivate various photocatalytic reactions for energy production and pollutant removal. In this review, the traits and recent research progress of Bi-based semiconductors and recent achievements in the synthesis methods of Bi-based direct Z-scheme heterojunction photocatalysts are explored. The recent photocatalytic applications development of Bi-based Z-scheme heterojunction photocatalysts in environmental pollutants removal and detection, water splitting, CO₂ reduction, and air (NO_x) purification are also described concisely. The challenges and future perspective in the studies of Bi-based Z-scheme heterojunction photocatalysts are discussed and summarized in the conclusion of this mini review.

Novel Bi2+xWO6 p-n Homojunction Nanostructure: Preparation, Characterization, and Application for a Self-Powered Cathodic Photoelectrochemical Immunosensor

Synthesizing novel cathodic photoactive materials with high photoelectrochemical (PEC) performance is urgently important for the development of photocathodic sensors. Herein, a novel photocathode material, Bi self-doped Bi₂WO₆ (i.e., Bi_2+xWO₆) p-n homojunction, is prepared via a simple ethylene glycol-assisted solvothermal reduction for the first time. Compared with pristine Bi₂WO₆, Bi_2+xWO₆ possesses a narrower band gap and higher light harvesting ability. Among the synthesized materials, Bi_2.1WO₆ exhibits the highest photocurrent response, which is 23 times that of pure Bi₂WO₆ because of the synergistic effect of doped Bi and the p-n homojunction. The open circuit potential, "V-shaped" Mott-Schottky plot, linear sweep voltammetry curve, and transient photocurrent demonstrate the p-n homojunction characteristics of the material well. By using the Bi_2+xWO₆ p-n homojunction as the photocathode for sensing and the plasmonic WO₃/Au composite as the photoanode for signal amplification, a new self-powered membraneless PEC immunosensor is established for a highly sensitive detection of human epididymal protein 4. This study offers a new idea for designing novel photocatalysts with satisfactory performance, and the Bi_2+xWO₆ p-n homojunction is expected to act as a promising PEC platform for developing various self-powered biosensors.

Enhanced photocatalytic destruction of pollutants by surface W vacancies in VW-Bi2WO6 under visible light

W vacancies containing Bi₂WO₆ (V_W-Bi₂WO₆) was synthesized by a reductant-involved hydrothermal process. The photoactivity of Bi₂WO₆ was enhanced by 3.3 times and the TOC removal rate increased from 38.3% to 64.7% after the introduction of surface W vacancies. Positron annihilation spectrometry (PAS), XPS, Raman spectra and other characterization results indicated that W vacancies existed on the catalyst surface. The surface W vacancies were proved to widen the band gap and negatively shift CB edge to produce more O₂^•- and photoexcited holes at catalyst surface, as confirmed by ESR and radicals trapping experiments. Further, according to the results of pyridine adsorbed FTIR and Zeta potentials, the enhanced interaction between pollutants and V_W-Bi₂WO₆ was confirmed. As a result, the active species produced at surface were able to be accelerated to directly react with organic pollutants, leading to the highly efficient degradation and mineralization of pollutants in water.

Target-triggered "signal-off" electrochemical aptasensor assisted by Au nanoparticle-modified sensing platform for high-sensitivity determination of circulating tumor cells

In this study, we fabricated a high-sensitivity "signal-off" electrochemical aptasensing platform for quantifying circulating tumor cells (CTCs) based on target-triggered signal readout of methylene blue (MB). Au nanoparticles (AuNPs) were introduced to enlarge the specific surface area of the gold electrode (GE), which would immobilize homogeneous and more MB-aptamers. MB-modified and stem-loop-like aptamers were assigned as a recognition element with K562 cells. Thiolated complementary strands hybridized with MB-aptamers to form double-stranded DNA (dsDNA) conformation which were further self-assembled on the surface of AuNP-modified GE, leading to a marked current peak of MB signal. In the presence of K562 cells, the MB-aptamers preferred to recognize and bind with the cells, causing the disassembly of MB-aptamers from the GE surface. Therefore, the reduced value of MB signal was related to the number of K562 cells. With the proposed aptasensor, a dynamic linear range from 1 × 10² to 1 × 10⁶ cells mL^-1 was obtained with a detection limit of 23 cells mL^-1. Moreover, the aptasensor showed good selectivity, stability, and reproducibility as well as potential use in the clinical setting. Meanwhile, characterization techniques such as field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, atomic force microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy were performed to analyze the evolution of the morphology and each fabricated step of the constructed aptasensor. Our proposed aptasensor could be designed as a universal platform for CTC determination by replacing tumor cell-specific aptamers, which is a promising strategy for basic research and clinical applications. Graphical abstract.

Zinc and Molybdenum Co-Doped BiVO4 Nanoarray for Photoelectrochemical Diethylstilbestrol Analysis Based on the Dual-Competitive System of Manganese Hexacyanoferrate Hydrate Nanocubes

This study proposes a competitive photoelectrochemical (PEC) immunosensor for detecting diethylstilbestrol (DES). The PEC sensing platform uses a zinc and molybdenum codoped BiVO₄ nanoarray ((Zn,Mo):BiVO₄) as the photoactive matrix and manganese hexacyanoferrate hydrate loading silicon dioxide layer composite nanocubes (MHCF@SiO₂ NCs) as the signal quencher. The (Zn,Mo):BiVO₄ nanoarray demonstrated brilliant PEC behavior, by virtue of the local electric field formed by the codoped Zn and Mo. This doping accelerated the electron transfer and improved the photoelectric conversion efficiency in BiVO₄ nanoarray under visible light. Furthermore, the nanoarray structure with its large surface area provided abundant binding sites for the immune response. As the MHCF@SiO₂ NCs-anti-DES competitively bonded with either free DES or bovine serum albumin conjugated DES (BSA-DES), hydrogen peroxide (H₂O₂) as electron donor was competitively consumed and meanwhile steric resistance blocked electrons transfer. For the above reasons, the photocurrent signal was reduced. Thus, the standard sample free DES was accurately detected, and the fabricated PEC immunosensor displayed an outstanding photocurrent response from 0.1 pg/mL to 50 ng/mL with a detection limit of 0.05 pg/mL. Simultaneously, the acceptable stability, selectivity, and reproducibility of the designed dual-competitive sensing platform suggest its applicability to small molecule detection.

A competitive immunoassay for electrochemical impedimetric determination of chlorpyrifos using a nanogold-modified glassy carbon electrode based on enzymatic biocatalytic precipitation

A direct competitive impedimetric immunoassay for chlorpyrifos (CPF) was developed that is based on the specific affinity of immunoassay and the enzymatic biocatalytic precipitation amplification strategy. The CPF antibody (anti-CPF) was anchored onto an electro-deposited nanogold modified glassy carbon electrode surface by adsorption of the Au-NH₂ bond and Au-SH bond. This improved the electrode reactivity and the loading amount of anti-CPF. Abundant horseradish peroxidase (HRP) and bovine serum albumin-CPF (BSA-CPF) were anchored onto spherical gold nanoparticles (AuNPs, 16 ± 2 nm) to form HRP-AuNP-BSA-CPF (analyte competitor). CPF determination was achieved when the competitive immunoassay occurred between CPF and analyte competitor with anti-CPF. In the presence of H₂O₂ and 4-chloro-1-naphthol, an enzyme-mediated biocatalytic precipitation process was triggered and produced an insoluble 4-chloro-1(4H)-naphthalenone. This insoluble substance increased the Faradaic impedance of the base electrode. The impedimetric signal was determined at the formal potential of 220 mV and alternating voltage of 10 mV. This signal decreased with increasing concentration of CPF over a linear range of 1.0 × 10^-3 ng mL^-1~10 ng mL^-1 with a detection limit of 0.070 pg mL^-1. The immunoassay has been tested for determination of chlorpyrifos in complex matrices such as artificially spiked vegetables with recoveries in the range 85 to 110%. The relative standard deviations were less than 7.5%. Graphical abstractSchematic representation of electrochemical impedimetric immunoassay for chlorpyrifos determination before enzymatic biocatalytic precipitation (BCP, red line) process and after BCP process (blue line).

A Novel Multifunctional p-Type Semiconductor@MOFs Nanoporous Platform for Simultaneous Sensing and Photodegradation of Tetracycline

p-Type semiconductors enable new opportunities for the development of photocatalysts. Metal-organic frameworks (MOFs) could now be manufactured for a wide range of applications. The zeolitic imidazolate framework-8 (ZIF-8), in particular, shows important desirable properties like good stability and a high surface area. Considering the p-type semiconducting intrinsic catalytic performance of CuBi₂O₄ (CBO) and the unique porous nanostructure and stability of ZIF-8, in this paper, we innovatively propose and investigate a new p-type semiconductor@MOFs (CBO@ZIF-8) material. Moreover, we focus on its application as a novel dual-function platform for simultaneous detection and degradation. The experimental results reveal that the platform is well suited for absorption, degradation, and fluorescent detection of certain targets. Using the contaminant, antibiotic tetracycline, as an example, the platform confirms excellent fluorescence sensing performance and good photodegradation properties under visible light. These results could aid the future design and implementation of novel and more sophisticated multifunction p-type semiconductor@MOFs platforms. The presented strategy represents the early stages of a future, genuine, general, multifunction platform.

Facile synthesis of a direct Z-scheme BiOCl–phosphotungstic acid heterojunction for the improved photodegradation of tetracycline

A one-step hydrothermal approach for synthesizing BiOCl–phosphotungstic acid (BiOCl–HPW) heterojunctions is proposed. The prepared BiOCl–HPW heterojunction exhibited good stability and photocatalytic activity.

A distance-triggered signaling on–off mechanism by plasmonic Au nanoparticles: toward advanced photocathodic DNA bioanalysis

An advanced signaling on–off mechanism was first proposed by integrating exciton–plasmon coupling and exciton energy transfer into cathodic PEC bioassays for ultrasensitive and specific detection of tDNA.