Target-regulated photoactivities of CdS/Ni-MOF heterojunction with [Ru(bpy)2dppz]2+ intercalator: a bisphenol A photoelectrochemical aptasensor.

Bisphenol A (BPA), an important endocrine disrupting compound, has infiltrated human daily lives through electronic devices, food containers, and children's toys. Developing of novel BPA assay methods with high sensitivity holds tremendous importance in valuing the pollution state. Here, we constructed an ultrasensitive photoelectrochemical (PEC) aptasensor for BPA determination by regulating photoactivities of CdS/Ni-based metal-organic framework (CdS/Ni-MOF) with [Ru(bpy)2dppz]2+ sensitizer. CdS/Ni-MOF spheres exhibited excellent photocatalytic performance, serving as a potential sensing platform for the construction of target recognition process. [Ru(bpy)2dppz]2+ were embedded into DNA double-stranded structure, functioning as sensitizer for modulating the signal response of the developed PEC aptasensor. The proposed PEC sensor exhibited outstanding analytical performances, including a wide linear range (0.1 to 1000.0 nM), low detection limit (0.026 nM, at 3σ/m), excellent selectivity, and high stability. This work provides a perspective for the design of ideal photosensitive materials and signal amplification strategies and extends their application in environment analysis.

Bimetallic AuPt alloy/rod-like CeO2 nanojunctions with high peroxidase-like activity for colorimetric sensing of organophosphorus pesticides.

Organophosphorus pesticides (OP) have extensive applications in agriculture, while their overuse causes inevitable residues in food, soil, and water, ultimately being harmful to human health and even causing diverse dysfunctions. Herein, a novel colorimetric platform was established for quantitative determination of malathion based on peroxidase mimic AuPt alloy decorated on CeO2 nanorods (CeO2@AuPt NRs). The synthesized nanozyme oxidized colorless 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2. Besides, the oxidized TMB was inversely reduced by ascorbic acid (AA), which were originated from hydrolysis of L-ascorbic acid-2-phosphate (AA2P) with the assistance of acid phosphatase (ACP). Based upon this observation ACP analysis was explored by colorimetry, showing a wid linear range of 0.2 ~ 3.5 U L-1 and a low limit of detection (LOD = 0.085 U L-1, S/N = 3). Furthermore, malathion present in the colorimetric system inhibited the activity of ACP and simultaneously affected the generation of AA, in turn promoting the recovery of the chromogenic reaction. Based on this, the LOD was decreased to 1.5 nM (S/N = 3) for the assay of malathion with a wide linear range of 6 ~ 100 nM. This simple colorimetric platform provides some informative guidelines for determination of other pesticides and disease markers.

Label-free "signal-off" PEC aptasensor for determination of kanamycin based on 3D nanoflower-like FeIn2S4/CdS Z-scheme heterostructures.

Highly photoactive 3D nanoflower-like FeIn2S4/CdS heterostructures were synthesized by hydrothermal treatment and low-temperature cation exchange. The FeIn2S4/CdS displayed 14.5 times signal amplification in contrast to FeIn2S4 alone. It was applied as a photoactive substrate to construct a label-free photoelectrochemical (PEC) aptasensor for ultrasensitive determination of kanamycin (KAN). Under the optimal conditions, the constructed PEC aptasensor displayed a wide linear range (5.0 × 10-4 ~ 5.0 × 101 ng mL-1) and a low detection limit (S/N = 3) of 40.01 fg mL-1. This study provides some constructive insights for preparation of advanced photoactive materials and exhibits great potential for quantitative determination of antibiotics in foods and environmental samples.

Bifunctional photoelectrochemical aptasensor based on heterostructured Ag3PO4/Ag/TiO2 nanorod array for determination of two tumor markers.

Constructing of heterostructures can significantly improve the photoelectrical (PEC) response signal by promoting the migration and suppressing the recombination of photogenerated carries. A bifunctional PEC sensing platform was designed for simultaneous high-performance detection of mucin-1 (MUC1) and carcinoembryonic antigen (CEA), which was based on generated Z-scheme heterostructured Ag3PO4/Ag/TiO2 nanorod arrays (NAs) and enzyme-mediated catalytic precipitation by alkaline phosphatase (ALP) and Au/hollow Co3O4 polyhedron. The proposed aptasensor displayed linear ranges of 1.0-100 ng mL-1 and 0.1-50 ng mL-1 for MUC1 and CEA with limit of detections of 0.430 and 0.058 ng mL-1, respectively. This strategy offers potential applications for early diagnosis, monitoring progression, and even evaluating the prognosis of breast cancer in practice.

Magnetic-assisted exciton-plasmon interactions modulated Bi2S3 nanorods@MoS2 nanosheets heterojunction: towards a split-type photoelectrochemical sensing of profenofos.

A split-type photoelectrochemical (PEC) sensor was designed for the detection of profenofos (PFF) depending on the magnetic-assisted exciton-plasmon interactions (EPI) between the semiconductor substrate and Au NPs. The core-shell Bi2S3 nanorods@MoS2 nanosheets (Bi2S3 NRs@MoS2 NSs) heterostructure nanomaterial with fascinating performance was synthesized and used as the photovoltaic conversion substrate and signal molecules absorption platform. The PEC sensor is operated by co-incubating with the released Au NPs-cDNA from the surface of magnetic beads, originating from the target-triggered DNA double-stranded structure opening event. Due to the strong EPI effects, the photocurrent of Bi2S3 NRs@MoS2 NSs decreased and varied with the PFF concentrations. The proposed PEC sensor exhibited outstanding analytical performances, including a wide linear range (1.0 pg mL-1~1.0 µg mL-1), low detection limitation (0.23 pg mL-1, at 3 σ/m), excellent specificity, high stability, and applicability. Overall, this work provides a new signal strategy for PEC biosensors and extends its application in environmental analysis.

Novel Ultrasensitive Photoelectrochemical Cytosensor Based on Hollow CdIn2S4/In2S3 Heterostructured Microspheres for HepG2 Cells Detection and Inhibitor Screening.

Hepatocellular carcinoma is a life-threatening malignant tumor found around the world for its high morbidity and mortality. Therefore, it is of great importance for sensitive analysis of liver cancer cells (HepG2 cells) in clinical diagnosis and biomedical research. To fulfill this demand, hollow CdIn2S4/In2S3 heterostructured microspheres (termed CdIn2S4/In2S3 for clarity) were prepared by a two-step hydrothermal strategy and applied for building a novel photoelectrochemical (PEC) cytosensor for ultrasensitive and accurate detection of HepG2 cells through specific recognition of CD133 protein on the cell surface with the respective aptamer. The optical properties of CdIn2S4/In2S3 were investigated by UV-vis diffuse reflectance spectroscopy (DRS) and PEC technology. By virtue of their appealing PEC characteristics, the resultant PEC sensor exhibited a wider dynamic linear range from 1 × 102 to 2 × 105 cells mL-1 with a lower limit of detection (LOD, 23 cells mL-1), combined by evaluating the expression level of CD133 protein stimulated by metformin as a benchmarked inhibitor. This work opens a valuable and feasible avenue for sensitive detection of diverse tumor cells, holding great potential in early clinical diagnosis and treatment coupled by screening inhibitors.

A signal-off photoelectrochemical aptasensor for ultrasensitive 17ß-estradiol detection based on rose-like CdS@C nanostructure and enzymatic amplification.

Carbon-coated cadmium sulfide rose-like nanostructures (CdS@C NRs) were prepared via a facile solvothermal approach and used as the photoelectrochemical (PEC) sensing platform for the integration of functional biomolecules. Based on this, a novel "signal-off" PEC aptasensor mediated by enzymatic amplification was proposed for the sensitive and selective detection of 17ß-estradiol (E2). In the presence of E2, alkaline phosphatase-modified aptamer (ALP-apta) were released from the electrode surface through the specific recognition with E2, which caused the negative effect on PEC response due to the decrease of ascorbic acid (AA) produced by the ALP in situ enzymatic catalysis. The developed PEC aptasensor for detection of E2 exhibited a wide linear range of 1.0-250 nM, with the low detection limit of 0.37 nM. This work provides novel insight into the design of potential phoelectroactive materials and the application of signal amplification strategy in environmental analysis field.

Label-free electrochemical biosensor for determination of procalcitonin based on graphene-wrapped Co nanoparticles encapsulated in carbon nanobrushes coupled with AuPtCu nanodendrites.

A new label-free electrochemical immunosensor was constructed for quantitative detection of procalcitonin (PCT), by employing AuPtCu nanodendrites (AuPtCu NDs, prepared by a one-pot solvothermal method) and graphene-wrapped Co nanoparticles encapsulated in 3D N-doped carbon nanobrushes (G-Co@ NCNBs), obtained by self-catalyzed chemical vapor deposition as immune-sensing platform. Impressively, the home-made nanocomposite enlarged the highly accessible active sites and promoted the mass/electron transport, in turn showing the efficient synergistic catalysis towards H2O2 reduction, combined by greatly increasing the loading capacity of the PCT antibody (Ab). The as-constructed sensor displayed a dynamic linear range of 0.0001 ~ 100 ng mL-1 along with an ultra-low limit of detection (LOD = 0.011 pg mL-1, S/N = 3) and was further explored for determination of PCT in a diluted serum sample with acceptable results. The sensor provides some valuable guidelines for bioassay and early diagnosis of sepsis.

Nanoporous Semiconductor Electrode Captures the Quantum Dots: Toward Ultrasensitive Signal-On Liposomal Photoelectrochemical Immunoassay.

Liposomal photoelectrochemical (PEC) bioanalysis has recently emerged and exhibited great potential in sensitive biomolecular detection. Exploration of the facile and efficient route for advanced liposomal PEC bioanalysis is highly appealing. In this work, we report the split-type liposomal PEC immunoassay system consisting of sandwich immunorecognition, CdS quantum dots (QDs)-loaded liposomes (QDLL), and the release and subsequent capture of the QDs by a separated TiO2 nanotubes (NTs) electrode. The system elegantly operated upon the protein binding and lysis treatment of CdS QDLL labels within the 96-well plate, and then the CdS QDs-enabled sensitization of TiO2 NTs electrode. Exemplified by cardiac markers troponin I (cTnI) as target, the proposed system achieved efficient activation of TiO2 NTs electrode and thus the signal generation toward the split-type PEC immunoassay. This work features the first use of QDs for liposomal PEC bioanalysis and is expected to inspire more interests in the design and implementation of numerous QDs-involved liposomal PEC bioanalysis.

Liposome-Mediated in Situ Formation of AgI/Ag/BiOI Z-Scheme Heterojunction on Foamed Nickel Electrode: A Proof-of-Concept Study for Cathodic Liposomal Photoelectrochemical Bioanalysis.

This work reports the liposome-mediated in situ formation of the AgI/Ag/BiOI Z-scheme heterojunction on foamed nickel electrode for signal-on cathodic photoelectrochemical (PEC) bioanalysis. Specifically, in a proof-of-concept study, Ag nanoparticle-encapsulated liposomes were initially confined via the sandwich immunobinding and then processed to release numerous Ag+ ions, which were then directed to react with the BiOI/Ni electrode, resulting in the in situ generation of a AgI/Ag/BiOI Z-scheme heterojunction on the electrode. The enhanced cathodic signal could be correlated to the target concentration, which thus underlays a novel signal-on cathodic liposomal PEC bioanalysis strategy. Different from previous anodic liposomal PEC bioanalysis, this work features the first cathodic liposomal PEC bioanalysis on the basis of the in situ formation of a Z-scheme heterojunction. More generally, integrated with various biorecognition events, this protocol could serve as a common basis for addressing numerous targets of interest.

A Polymer Dots-Based Photoelectrochemical pH Sensor: Simplicity, High Sensitivity, and Broad-Range pH Measurement.

This work reported the photoelectrochemical (PEC) pH sensor for sensitive and broad-range pH measurement on the basis of semiconducting polymer dots (Pdots). The sensor was fabricated by immobilizing Pdots onto the surface of indium tin oxide (ITO). Experimental results revealed that the carboxylic acid groups of Pdots were sensitive to pH variation, which could result in conformational changes and further diffusion of carriers. Besides, different pH value could change the redox properties of the Pdots, and the photocurrent response was hence altered by the carriers produced on the Pdots. Further results demonstrated that the developed sensor exhibited variable photocurrent sensitively by responding to different pH values. This pH sensor is of high sensitivity, stability, and reversibility, which provides a bright prospect for future pH measurements in the bioanalytical field.

Cu Nanoclusters-Encapsulated Liposomes: Toward Sensitive Liposomal Photoelectrochemical Immunoassay.

Herein we report the strategy of liposome-mediated Cu2+-induced exciton trapping upon CdS quantum dots (QDs) for amplified photoelectrochemical (PEC) bioanalysis application. Specifically, the Cu nanoclusters (NCs)-encapsulated liposomes were first fabricated and then processed with antibodies bound to their external surfaces. After the sandwich immunocomplexing, the confined liposomal labels were subjected to sequential lysis treatments for the release of Cu NCs and numerous Cu2+ ions, which were then directed to interact with the CdS QDs electrode. The interaction of Cu2+ ions with CdS QDs could generate CuxS and form the trapping sites to block the photocurrent generation. Since the photocurrent inhibition is closely related with the Cu NCs-loaded liposomal labels, a novel and general "signal-off" PEC immunoassay could thus be tailored with high sensitivity. Meanwhile, a complementary "signal-on" fluorescent detection could be accomplished by measuring the fluorescence intensity originated from the Cu NCs. This work features the first use of Cu NCs in PEC bioanalysis and also the first NCs-loaded liposomal PEC bioanalysis. More importantly, by using other specific ions/reagents-semiconductors interactions, this protocol could serve as a common basis for the general development of a new class of liposome-mediated PEC bioanalysis.

Energy Transfer between Semiconducting Polymer Dots and Gold Nanoparticles in a Photoelectrochemical System: A Case Application for Cathodic Bioanalysis.

We report herein the energy transfer (ET) between semiconducting polymer dots (Pdots) and gold nanoparticles (Au NPs) in a photoelectrochemical (PEC) system and its feasibility for cathodic bioanalysis application. Specifically, COOH-capped Pdots were first fabricated and then assembled onto the indium-tin oxide (ITO) surface, followed by the modification of single-strand (ss) DNA probe (pDNA). After the DNA hybridization with the Au NP-tethered complementary ssDNA (Au NP-tDNA), the Au NPs were brought into the close proximity of Pdots. Upon light stimulation, photoluminescence (PL) was annihilated, fluorescence was attenuated, and the photocurrent intensity was evidently decreased. This ET-based PEC DNA sensor exhibited a linear range from 1 fM to 10 pM with a detection limit of 0.97 fM at a signal-to-noise ratio of 3. The present work first exploited the ET between Pdots and Au NPs, and we believe this phenomenon will spark new interest in the study of various Pdots-based ET-influenced PEC systems and thus catalyze increasing studies for specific bioanalytical purposes.

Photoelectrochemical-Chemical-Chemical Redox Cycling for Advanced Signal Amplification: Proof-of-Concept Toward Ultrasensitive Photoelectrochemical Bioanalysis.

Signal amplification is essential for ultrasensitive photoelectrochemical (PEC) bioanalysis. Exploration of the facile and efficient route for multiple signal amplification is highly appealing. Herein, we present the concept of photoelectrochemical-chemical-chemical (PECCC) redox cycling as an advanced signal amplification route and a proof-of-concept toward ultrasensitive PEC bioanalysis. The system operated upon the bridging between the enzymatic generation of signaling species ascorbic acid (AA) from a sandwich immunoassay and the PECCC redox cycling among the ferrocenecarboxylic acid as redox mediator, the AA, and the tris(2-carboxyethyl)phosphine as reducing agent at the Bi2S3/Bi2WO6 photoelectrode. Exemplified by myoglobin (Myo) as target, the proposed system achieved efficient regeneration of AA and thus signal amplification toward the ultrasensitive split-type PEC immunoassay. This work first exploited the PECCC redox cycling, and we believe it will attract more interest in the research of PEC bioassays on the basis of advanced redox cycling.

Enediol-Ligands-Encapsulated Liposomes Enables Sensitive Immunoassay: A Proof-of-Concept for General Liposomes-Based Photoelectrochemical Bioanalysis.

Sensitive photoelectrochemical (PEC) bioanalysis usually relies on enzyme-assisted signal amplification. This work describes the first proof-of-concept study for liposome-based PEC bioanalysis. Specifically, unilamellar liposomes were prepared and then utilized to carry the enediol-ligands and antibodies within their internal cavities and upon their external surfaces, respectively. On the other hand, the 96-well plate was used for accommodating the sandwich immunocomplexing, and then the confined liposomes were directed to release the encapsulated enediol-ligands into an individual well. The subsequent in situ sensitization of the TiO2 nanoparticles (NPs) electrode was then used to transduce the recognition events. This facile strategy allows for sensitive immunoassay without the involvement of laborious electrode fabrication and enzymatic amplification. Importantly, the protocol can be extended as a general PEC method for numerous other targets of interest. We believe this work could offer a new perspective for the rational implementation of various liposome complexes for novel PEC bioanalysis.

Self-shedding MOF-nanocarriers modulated CdS/MoSe2 heterojunction activity through in-situ ion exchange: An enhanced split-type photoelectrochemical sensor for deoxynivalenol.

Deoxynivalenol (DON), a mycotoxin produced by Fusarium, poses a significant risk to human health and the environment. Therefore, the development of a highly sensitive and accurate detection method is essential to monitor the pollution situation. In response to this imperative, we have devised an advanced split-type photoelectrochemical (PEC) sensor for DON analysis, which leverages self-shedding MOF-nanocarriers to modulate the photoelectric response ability of PEC substrate. The PEC sensing interface was constructed using CdS/MoSe2 heterostructures, while the self-shedding copper peroxide nanodots@ZIF-8 (CPNs@ZIF-8) served as the Cu2+ source for the in-situ ion exchange reaction, which generated a target-related signal reduction. The constructed PEC sensor exhibited a broad linear range of 0.1 pg mL-1 to 500 ng mL-1 with a low detection limit of 0.038 pg mL-1, demonstrating high stability, selectivity, and proactivity. This work not only introduces innovative ideas for the design of photosensitive materials, but also presents novel sensing strategies for detecting various environmental pollutants.

Dual amplification for PEC ultrasensitive aptasensing of biomarker HER-2 based on Z-scheme UiO-66/CdIn2S4 heterojunction and flower-like PtPdCu nanozyme.

As an important prognostic indicator in breast cancer, human epithelial growth factor receptor-2 (HER-2) is of importance for assessing prognosis of breast cancer patients, whose accurate and facile analysis are imperative in clinical diagnosis and treatment. Herein, photoactive Z-scheme UiO-66/CdIn2S4 heterojunction was constructed by a hydrothermal method, whose optical property and photoactivity were critically investigated by a range of techniques, combined by elucidating the interfacial charge transfer mechanism. Meanwhile, PtPdCu nanoflowers (NFs) were fabricated by a simple aqueous wet-chemical method, whose peroxidase (POD)-mimicking catalytic activity was scrutinized by representative tetramethylbenzidine (TMB) oxidation in H2O2 system. Taken together, the UiO-66/CdIn2S4 based photoelectrochemical (PEC) aptasensor was established for quantitative analysis of HER-2, where the detection signals were further magnified through catalytic precipitation reaction towards 4-chloro-1-naphthol (4-CN) oxidation (assisted by the PtPdCu NFs nanozyme). The PEC aptasensor presented a broader linear range within 0.1 pg mL-1-0.1 µg mL-1 and a lower limit of detection of 0.07 pg mL-1. This work developed a new PEC aptasensor for ultrasensitive determination of HER-2, holding substantial promise for clinical diagnostics.

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.

Dual II-scheme nanosheet-like Bi2S3/Bi2O3/Ag2S heterostructures for ultrasensitive PEC aptasensing of aflatoxin B1 coupled with catalytic signal amplification by dendritic nanorod-like Au@Pd@Pt nanozyme.

As one of the most toxic chemical substances, aflatoxin B1 (AFB1) has a strong carcinogenic effect even at a trace level in human and animal, which severely threatens human health and even causes cancers. Therefore, ultrasensitive detection of AFB1 is of significant importance. For such analysis, dual II-scheme sheet-like Bi2S3/Bi2O3/Ag2S heterostructures were prepared by the in-situ growth method, which exhibited high separation efficiency for the electron-hole (e--h+) pairs, prominent stability, and high photoactivity. Moreover, the dendritic nanorod-like Au@Pd@Pt (Au@Pd@Pt DNRs) nanozyme was homely synthesized, whose peroxidase-like activity was scrupulously investigated by catalytical oxidation of diaminobenzidine (DAB) in the presence of H2O2. Integration by the aptasensing strategy, a photoelectrochemical (PEC) "signal-on" aptasensor was prepared, which exhibited a broader linear range of 0.5 pg mL-1-100 ng mL-1 with a lower limit of detection (LOD = 0.09 pg mL-1, S/N = 3). This work provides a feasible strategy to develop advanced PEC biosensors for actual analysis of environmental pollutants.

Integration of phosphate functionalized Pt/TiO2 and Ru(bpy)32+ sensitization for ultrasensitive assay of adenosine deaminase activity on a novel split-typed PEC aptasensor.

To date, it is still a challenge for high-performance photoelectrochemical (PEC) assay of low-abundance adenosine deaminase (ADA) in fundamental research and clinical diagnosis. Herein, phosphate-functionalized Pt/TiO2 (termed PO43-/Pt/TiO2) was prepared as ideal photoactive material to develop a split-typed PEC aptasensor for detection of ADA activity, coupled by a Ru(bpy)32+ sensitization strategy. We critically studied the effects of the PO43- and Ru(bpy)32+ on the detection signals, and discussed the signal-amplified mechanism. Specifically, hairpin-structured adenosine (AD) aptamer was splited into single chain via ADA-induced catalytic reaction, and subsequently hybridized with complementary DNA (cDNA, initially coating on magnetic beads). The in-situ formed double-stranded DNA (dsDNA) was further intercalated by more Ru(bpy)32+ to amplify the photocurrents. The resultant PEC biosensor showed a broader linear range of 0.05-100 U L-1 and a lower limit of detection (0.019 U L-1), which can fill the blank for analysis of ADA activity. This research would provide some valuable insights for building advanced PEC aptasensors in ADA-related research and clinical diagnosis.