Target-induced nano-enzyme reactor mediated hole-trapping for high-throughput immunoassay based on a split-type photoelectrochemical detection strategy

Sensitive, Semiquantitative, and Portable Nucleic Acid Detection of Rabies Virus Using a Personal Glucose Meter

Rabies is a zoonotic infection with the potential to infect all mammals and poses a significant threat to mortality. Although enzyme-linked immunosorbent tests and real-time reverse transcription-quantitative polymerase chain reaction (RT-qPCR) have been established for rabies virus (RABV) detection, they require skilled staff. Here, we introduce a personal glucose meter (PGM)-based nucleic acid (NA-PGM) detection method to diagnose RABV. This method ensures sensitive and convenient RABV diagnosis through hybridization of reverse transcription-recombinase aided amplification (RT-RAA) amplicons with probes labeled with sucrose-converting enzymes, reaching a detection level as low as 6.3 copies/μL equivalent to 12.26 copies. NA-PGM allows for the differentiation of RABV from other closely related viruses. In addition, NA-PGM showed excellent performance on 65 clinical samples with a 100% accuracy rate compared with the widely adopted RT-qPCR method. Thus, our developed NA-PGM method stands out as sensitive, semiquantitative, and portable for RABV detection, showcasing promise as a versatile platform for a wide range of pathogens.

Atomic Engineering of Single-Atom Nanozymes for Biomedical Applications

Single-atom nanozymes (SAzymes) showcase not only uniformly dispersed active sites but also meticulously engineered coordination structures. These intricate architectures bestow upon them an exceptional catalytic prowess, thereby captivating numerous minds and heralding a new era of possibilities in the biomedical landscape. Tuning the microstructure of SAzymes on the atomic scale is a key factor in designing targeted SAzymes with desirable functions. This review first discusses and summarizes three strategies for designing SAzymes and their impact on reactivity in biocatalysis. The effects of choices of carrier, different synthesis methods, coordination modulation of first/second shell, and the type and number of metal active centers on the enzyme-like catalytic activity are unraveled. Next, a first attempt is made to summarize the biological applications of SAzymes in tumor therapy, biosensing, antimicrobial, anti-inflammatory, and other biological applications from different mechanisms. Finally, how SAzymes are designed and regulated for further realization of diverse biological applications is reviewed and prospected. It is envisaged that the comprehensive review presented within this exegesis will furnish novel perspectives and profound revelations regarding the biomedical applications of SAzymes.

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.

Progress in Electrochemical Immunosensors with Alkaline Phosphatase as the Signal Label

Electrochemical immunosensors have shown great potential in clinical diagnosis, food safety, environmental protection, and other fields. The feasible and innovative combination of enzyme catalysis and other signal-amplified elements has yielded exciting progress in the development of electrochemical immunosensors. Alkaline phosphatase (ALP) is one of the most popularly used enzyme reporters in bioassays. It has been widely utilized to design electrochemical immunosensors owing to its significant advantages (e.g., high catalytic activity, high turnover number, and excellent substrate specificity). In this work, we summarized the achievements of electrochemical immunosensors with ALP as the signal reporter. We mainly focused on detection principles and signal amplification strategies and briefly discussed the challenges regarding how to further improve the performance of ALP-based immunoassays.

PB@PDA nanocomposites as nanolabels and signal reporters for separate-type cathodic photoelectrochemical immunosensors in the detection of carcinoembryonic antigens

Photoelectrochemical (PEC) immunoassays exhibiting high sensitivity and decent operability have considerable potential in areas such as cancer diagnostics. In particular, cathodic PEC configurations can prevent interference from reductive substances, which can occur in biological samples; however, challenges remain in terms of sensitivity and operability. In this study, separate-type PEC immunoassays were developed for carcinoembryonic antigen (CEA) by combining microplate-based immune recognition and off-on cathodic PEC detection. Polydopamine (PDA)-coated Prussian blue (PB) nanoparticles (PB@PDA NPs) were used as signal tags to label the detection antibody. The PB NPs and PDA captured on the microplates both disassembled under strongly alkaline conditions to generate redox-active electron acceptors. The disassembled products were quantitatively transferred to PEC detection cells and synergistically enhanced the PEC current with microstructured BiOI, which operated as a cathodic semiconductor electrode. As proof of principle, carcinoembryonic antigen (CEA) was applied to elucidate the potential application of PEC immunoassay in clinical diagnosis, and the obtained linear range of the sensor was 0.001-100 ng mL^-1 with the detection limit of 54.9 fg mL^-1 (S/N = 3). The proposed separate-type off-on PEC strategy showed high sensitivity and decent operability for CEA detection, indicating its potential for the identification of other tumor markers.

Covalent organic frameworks with high quantum efficiency in sacrificial photocatalytic hydrogen evolution

Organic semiconductors offer a tunable platform for photocatalysis, yet the more difficult exciton dissociation, compared to that in inorganic semiconductors, lowers their photocatalytic activities. In this work, we report that the charge carrier lifetime is dramatically prolonged by incorporating a suitable donor-acceptor (β-ketene-cyano) pair into a covalent organic framework nanosheet. These nanosheets show an apparent quantum efficiency up to 82.6% at 450 nm using platinum as co-catalyst for photocatalytic H₂ evolution. Charge carrier kinetic analysis and femtosecond transient absorption spectroscopy characterizations verify that these modified covalent organic framework nanosheets have intrinsically lower exciton binding energies and longer-lived charge carriers than the corresponding nanosheets without the donor-acceptor unit. This work provides a model for gaining insight into the nature of short-lived active species in polymeric organic photocatalysts.

Recent advances in biological detection with rolling circle amplification: design strategy, biosensing mechanism, and practical applications

Rolling circle amplification (RCA) is a simple and isothermal DNA amplification technique that is used to generate thousands of repeating DNA sequences using circular templates under the catalysis of DNA polymerase.

Controllable signal molecule release from Au NP-gated MSNs for photocathodic detection of ultralow level AβO

By integrating a target-responsive MSN-based controlled release system with a sensitization-SPR co-enhanced thionine/MoS₂ QDs/Cu NWs photocathode, a highly sensitive split-type PEC aptasensing platform for AβO detection in blood is constructed. Ultralow detection limit (2.1 fM) and high selectivity show great potential in early AD diagnosis.

Photoelectrochemical analysis of the alkaline phosphatase activity in single living cells

Conventional photoelectrochemical (PEC) analysis mostly utilizes photoactive material modified planar indium tin oxides (ITOs) to obtain photocurrent responses for the measurement of analytes in solution. In this work, a CdS quantum dot (QD) modified nanopipette was prepared for the PEC analysis of the alkaline phosphatase (ALP) activity in single MCF-7 cells. The nanopipette was filled with ascorbic acid 2-phosphate (AAP) that was egressed outside the nanopipette by electrochemical pumping. Next, AAP was catalyzed by ALP to generate ascorbic acid (AA), which is an efficient electron donor for CdS QDs under illumination. Based on the result that the nanopipette showed a linear photocurrent response to AA, a nearly linear correlation between the photocurrent and the activity of ALP was established. Accordingly, using these CdS QD modified nanopipettes, the ALP activity in single MCF-7 cells was determined to be 0.12 U mL^-1 by PEC analysis. This work does not expand the application of PEC bioanalysis, but offers a new strategy for single cell analysis.

Electrochemical Polymerization Induced Chirality Fixation of Crystalline Pillararene-Based Polymer and Its Application in Interfacial Chiral Sensing

A new strategy has been developed for the direct chirality fixation, which is induced by electrochemical polymerization, of macrocyclic hosts pillar[5]arene. Taking advantage of electrochemical polymerization, thiophene-modified pillar[5]arene monomers (Th-P[5]A) have been regularly arranged under the action of an electric field to form chiral nanofiber-like crystalline pillar[5]arene-based polymers (poly-Th-P[5]A), showing a significant circular dichroism (CD) signal. With the active photochemical properties, poly-Th-P[5]A is first used as a photoelectrochemical (PEC) chiral sensor for the identification and determination of l- and d-ascorbic acid (l-AA, d-AA) without adding any extra photoactive probes. Importantly, the chiral recognition between poly-Th-P[5]A and l-AA also triggers a polarity conversion for the photocurrent of the polymer, and it greatly results in a broad chiral detection range for l-AA, crossing 6 orders of magnitude. This work provides a promotional strategy for building a PEC chiral recognition platform based on pillararenes.

Recent advances in DNA walker machines and their applications coupled with signal amplification strategies: A critical review

DNA walkers, a type of dynamic nanomachines, have become the subject of burgeoning research in the field of biology. These walkers are powered by driving forces based on strand displacement reactions, protein enzyme/DNAzyme reactions and conformational transitions. With the unique properties of high directionality, flexibility and efficiency, DNA walkers move progressively and autonomously along multiple dimensional tracks, offering abundant and promising applications in biosensing, material assembly and synthesis, and early cancer diagnosis. Notably, DNA walkers identified as signal amplifiers can be combined with various amplification approaches to enhance signal transduction and amplify biosensor sensing signals. Herein, we systematically and comprehensively review the walking principles of various DNA walkers and the recent progress on multiple dimensional tracks by presenting representative examples and an insightful discussion. We also summarized and categorized the diverse signal amplification strategies with which DNA walkers have coupled. Finally, we outline the challenges and future trends of DNA walker machines in emerging analytical fields.

Application of electrochemical methods for the detection of abiotic stress biomarkers in plants

Abiotic stress is the main cause of low productivity in plants. Therefore, it is important to detect stress and respond to it in a timely manner to avoid irreversible damage to plant productivity and health. The application of traditional methods in agriculture is limited by expensive equipment and cumbersome sample processing. More effective detection methods are urgently needed due to the trace amounts and low stabilities of plant biomarkers. Electrochemical detection methods have the unique advantages of high accuracy, a low detection limit, fast response and easy integration with systems. In this review, the application of three types of electrochemical methods to phytohormone assessment is highlighted including direct electrochemical, immunoelectrochemical, and photoelectrochemical methods. Research on electrochemical methods for detecting abiotic stress biomarkers, including various phytohormones, is also summarized with examples. To date, the detection limit of exogenous plant hormones can reach pg/mL or even lower. Nevertheless, more efforts need to be made to develop a portable instrument for in situ online detection if electrochemical sensors are to be applied to the detection of the endogenous hormones or the physiological state of plants. Additionally, plant-wearable sensors that can be directly attached to or implanted into plants for continuous, noninvasive and real-time monitoring are emphasized. Finally, rational summaries of the considered methods and present challenges and future prospects in the field of abiotic stress detection-based electrochemical biosensors are thoroughly discussed.

Protein detection based on rolling circle amplification sensors

Rolling circle amplification (RCA) is an isothermal process under the action of DNA polymerases. Large-scale DNA templates have been generated using RCA for target detection. Some signal amplification strategies including optical sensors and electrochemical sensors based on RCA have been applied to achieve sensitive detection. Sensors based on RCA have attracted increasing interest. Advances in RCA-based sensors for protein detection are reviewed in this paper. The advantages and detection mechanisms of sensors based on RCA are revealed and discussed. Finally, possible challenges and future perspectives are also outlined.

Ionic Current Rectification Triggered Photoelectrochemical Chiral Sensing Platform for Recognition of Amino Acid Enantiomers on Self-Standing Nanochannel Arrays

Chirality is an intrinsic and essential property of nature, and the enantiomeric discrimination of chiral molecules can provide important information leading to a better understanding of chiral recognition in biological systems and furthering the development of useful molecular devices in biochemical and pharmaceutical studies. Therefore, the exploration of new detection techniques with high accuracy and reliability for high-throughput enantioselective detection is still highly desirable. Herein, a chiral enantiomers selective recognition platform based on self-standing titanium dioxide nanochannel arrays (TiO₂ NCAs) is proposed to implement the ionic current rectification triggered photoelectrochemical (PEC) detection, which provides a novel sensing platform to discriminate chiral amino acid through synchronous output dual response signals of ionic current and photocurrent. The utilization of nanochannel arrays guaranteed the high-throughput detection, and the dual signal model avoided a "false positive" detection. In addition, based on the fabricated detection platform, various chiral substances can be facilely detected through integrating different chiral regulation units, which shed light on the construction of reliable chiral sensors for practical applications in a biological environment.

Selective Electrochemical Capture and Release of Heparin Based on Amine-Functionalized Carbon/Titanium Dioxide Nanotube Arrays

Heparin (HEP) is a sulfated glycosaminoglycan that is a clinical anticoagulant agent. Commercially derived from porcine intestinal mucosa, HEP is challenging to separate from this complex biological mixture for additional purification. This study aimed to raise the purity of isolated HEP using electrochemical potential to increase its selective capture and release. We demonstrate an electrochemical platform featuring an anode composed of amine-functionalized carbon/titanium dioxide nanotube arrays on titanium foil (Ti/C-TNTAs-NH₂) and a cathode made of expanded graphite. Our results show that Ti and Ti/C-TNTAs control plates do not adsorb HEP, even while applying an external potential to the cell. However, when the Ti/C-TNTAs electrode is modified by 3 aminopropyltriethoxysilane, the terminal NH₂ groups provide a high density of positive charges that serve as binding sites, enabling the adsorption of HEP. This attraction is further strengthened by applying an external potential to the anode. Subsequent release of the HEP molecules and regeneration of the Ti/C-TNTAs-NH₂ electrode are easily accomplished by applying an anodic potential to the plate, as well as by increasing the concentration of NaCl in solution. This electrochemical system demonstrates the good selectivity of HEP, even within a mixture of other probable interfering species (e.g., bovine serum albumin and chondroitin sulfate). Additionally, it maintains 90.11% of its initial electrosorption efficiency after ten repeated HEP adsorption/desorption cycles, indicating this system's promising stability and reusability for HEP purification.

Simple "signal-on" photoelectrochemical aptasensor for ultrasensitive detecting AFB1 based on electrochemically reduced graphene oxide/poly(5-formylindole)/Au nanocomposites

A simple "signal-on" photoelectrochemical (PEC) aptasensor is constructed for Aflatoxin B1 (AFB1) detection based on electrochemically reduced graphene oxide/poly(5-formylindole)/Au (erGO/P5FIn/Au) nanocomposites. The nanocomposites are synthesized by simple electrochemical deposition method and show good photoelectrochemical performance. Poly(5-formylindole) (P5FIn) can generate electron-hole pairs under light irradiation, leading to the formation of robust cathode photocurrent. Au can be acted as signal amplifier due to the high conductivity. The erGO is used to immobilize AFB1 aptamer chain by π-π stacking interaction between the carbon six-membered ring in graphene and the C-N heterocyclic ring in nucleobases of ssDNA. After the insulating AFB1 aptamer chain is fixed to the electrode, the signal of PEC sensor is "OFF". In the process of AFB1 detection, the aptamer chain detaches from the surface of erGO, which results in "ON" of the sensor signal. Based on this design, this constructed PEC aptasensor shows a high sensitivity for AFB1 with a wide linear detection range (LDR) from 0.01 ng mL^-1 to 100 ng mL^-1. The limit of detection (LOD) is 0.002 ng mL^-1. This PEC sensor also exhibits good stability, selectivity, specificity, and satisfactory practical sample analysis ability. This work may provide a new promising PEC platform for AFB1 detection as well as some other small molecules analysis.

Ultra-sensitive electrochemical detection of bacteremia enabled by redox-active gold nanoparticles (raGNPs) in a nano-sieving microfluidic system (NS-MFS)

Early diagnosis of bacterial infections is crucial to improving survival rates by enabling treatment with appropriate antibiotics within the first few hours of infection. This paper presents a highly sensitive amperometric biosensor for the detection of several pathogenic bacterial cells in blood plasma around 30 min. The proposed device is based on an electropolymerized self-assembled layer on gold nanoparticles operated in a portable nano-sieving microfluidic system (NS-MFS). The redox-active gold nanoparticles (raGNPs) enhanced the electrical conductivity and provided a greater number of electrochemically active molecules for sensing, while improving resistance to the fouling of sensors by oxidation products in blood plasma. The detection limit of the device has been shown to reach 10 CFU/mL for Pseudomonas aeruginosa and Staphylococcus aureus spiked in plasma. The dynamic range of the sensing system falls between 10 and 10⁵ CFU/mL in a buffer solution by cyclic voltammetry (CV) measurements. The results demonstrated that the raGNPs/NS-MFS can successful detect P. aeruginosa and S. aureus in human plasma, and is very useful for the diagnosis of bacteremia from clinical samples.

A chemiresistive thin-film translating biological recognition into electrical signals: an innovative signaling mode for contactless biosensing

An innovative signaling mode in which a chemiresistive thin-film electrode monitors the specific gaseous component that results from a biological recognition event to indirectly detect targets in the liquid phase is developed for highly-efficient contactless biosensing. This signaling mode may open a new horizon in designing robust biosensing devices for bioanalysis.

Gold Nanoparticle Couples with Entropy-Driven Toehold-Mediated DNA Strand Displacement Reaction on Magnetic Beads: Toward Ultrasensitive Energy-Transfer-Based Photoelectrochemical Detection of miRNA-141 in Real Blood Sample

Highly stable circulating microRNAs (miRNAs) are currently recognized as a novel potential biomarker for clinical cancer diagnosis in the early stage. However, limited by its low concentration, high sequence similarity, as well as the numerous interferences in body fluids, detection of miRNA in whole blood with sufficient selectivity and sensitivity is still challenging. Herein, we reported the integration of entropy-driven toehold-mediated DNA strand displacement (ETSD) reaction with magnetic beads (MB) toward the energy-transfer-based photoelectrochemical (PEC) detection of the prostate carcinoma (PCa) biomarker miRNA-141 in a real blood sample. In this protocol, the ETSD reaction was divided into two steps, and cooperated with magnetic separation, target extraction and amplification could be realized in a single test and ultrasensitive detection of miRNA-141 could be achieved in undiluted whole blood sample. This work proposed a new solution for sensitive biomolecular detection in a complex biological milieu and exhibited great promise for future clinical cancer diagnosis.

High-Throughput Signal-On Photoelectrochemical Immunoassay of Lysozyme Based on Hole-Trapping Triggered by Disintegrating Bioconjugates of Dopamine-Grafted Silica Nanospheres

A unique split-type photoelectrochemical (PEC) immunoassay has been constructed for detection of low-abundance biocompounds (lysozyme, Lyz, used in this case) via a new trigger strategy by disintegrating bioconjugates of dopamine-grafted silica nanospheres (DA@SiO₂NSs) for signal amplification. The preferred electron donor assembly of DA@SiO₂NSs is first used as a molecular printboard for positioning anti-Lyz secondary antibody (Ab₂) through an amide reaction. With specific immunoreactions in a high-binding microplate, a sandwich immunoassay, the DA@SiO₂NSs-based bioconjugate is achieved. By initiating the disintegration of the bioconjugates via acid etching, numerous electron donors of DA are released, thus efficiently triggering hole-trapping with amplified signals obtained. The smart integration of ZnIn₂S₄-based heterojunctions as photoactive material, a split-type detection mode, and a new trigger strategy by disintegrating the DA@SiO₂NSs-based bioconjugate offer an attractive high-throughput signal-on PEC immunoassay for detection of Lyz. Such an unusual PEC sensor exhibits an outstanding linear response to the concentration in the range between 0.002 and 500 ng mL^-1, and the detection limit is as low as 0.6 ppt ( S/ N = 3). The as-fabricated assay is cost-effective and sensitive. It has been successfully used for measuring Lyz in real samples, which demonstrates great promise for practical applications.

An efficient nonlinear hybridization chain reaction-based sensitive fluorescent assay for in situ estimation of calcium channel protein expression on bone marrow cells

A sensitive and highly efficient approach to monitor the expression of proteins on live cells was urgently needed to demonstrate its factor and mechanism and most important for clinical diagnostics and molecular biology. Herein, we developed a simple and highly efficient strategy, nonlinear hybridization chain reaction (nonlinear HCR), for the sensitive determination of proteins on live cells with transient receptor potential vanilloid 4 (TRPV4) and RAW264.7 cells as a model. Unlike the normal hybridization chain reaction (HCR) with multiplicative amplification, an exponential amplified fluorescent response could be obtained in theory based on the proposed nonlinear HCR. As a result, the nonlinear HCR generated a significant enhancement about 3 times compared with the normal HCR and 10 times compared with the directly immunofluorescence assay. Based on the proposed nonlinear HCR, the fluorescent signals increased with the concentration of TRPV4 in the range from 10 pg/mL to 100 ng/mL with a detection limit of 2.8 pg/mL, which would be useful for the sensitive detection of proteins in cell lysis or on cell surface. At the same time, the significant improvements via nonlinear HCR were achieved in the fluorescent imaging system compared with traditional immunofluorescence staining and normal HCR, proving the significant value of nonlinear HCR-based amplification strategy. Success in the establishment of the highly efficient nonlinear HCR strategy offered a simple and sensitive approach to demonstrate the concentration of special proteins on cell and other proteins and nucleotide potentially, revealing a simple and efficient technology for research fields of clinical diagnostics and molecular biology.

Dual-Modal Split-Type Immunosensor for Sensitive Detection of Microcystin-LR: Enzyme-Induced Photoelectrochemistry and Colorimetry

Microcystins, the lethal cyanotoxins from Microcystis aeruginosa, can inhibit the activity of protein phosphatase and promote liver tumors. Herein, a dual-modal split-type immunosensor was constructed to detect microcystin-LR (MC-LR), based on the photocurrent change of CdS/ZnO hollow nanorod arrays (HNRs) and the blue shift of the surface plasmon resonance peak from Au nanobipyramids@Ag. By using mesoporous silica nanospheres as the carrier to immobilize secondary antibody and DNA primer, a hybridization chain reaction was adopted to capture alkaline phosphatase, while its catalytic reaction product, ascorbic acid, exhibited dual functions. The detailed mechanism was investigated, showing that ascorbic acid can not only act as the electron donor to capture the holes in CdS/ZnO-HNRs, leading to the increase photocurrent, but also as the reductant to form silver shells on Au nanobipyramids, generating multiply vivid color variations and blue shifts. Compared with the traditional photoelectrochemical immunosensor or colorimetric method for MC-LR, a more accurate and reliable result can be obtained, due to different mechanisms and independent signal transduction. Therefore, this work can not only propose a new dual-modal immunosensor for MC-LR detection but also provide innovative inspiration for constructing sensitive, accurate, and visual analysis for toxins.

Photogenerated Hole-Induced Chemical Redox Cycling on Bi2S3/Bi2Sn2O7 Heterojunction: Toward General Amplified Split-Type Photoelectrochemical Immunoassay

This work reports the elegant bridging of enzymatic generation of electron donor with photogenerated hole-induced chemical redox cycling amplification (RCA) for innovative photoelectrochemical (PEC) immunoassay, by the aid of a heterojunction photoelectrode with split-type strategy. Specifically, the system was exemplified by the alkaline phosphatase (ALP) catalytic generation of ascorbic acid (AA), the redox cycling of AA by tris (2-carboxyethyl) phosphine (TCEP) as reductant, and the use of a novel Bi₂S₃/Bi₂Sn₂O₇ heterojunction and myoglobin (Myo) as the photoelectrode and the target, respectively. After the immunoreaction and ALP-induced production of AA, the subsequent oxidation of AA by the photogenerated holes of the Bi₂S₃/Bi₂Sn₂O₇ heterojunction could be cycled via the regeneration of AA by TCEP from the oxidized product of dehydroascorbic acid, leading to easy signal amplification for the sensitive immunoassay of Myo in real samples. It is believed that this work provided a basis for further design and development of general RCA-based PEC immunoassays.

A novel "signal-on" photoelectrochemical sensor for ultrasensitive detection of alkaline phosphatase activity based on a TiO2/g-C3N4 heterojunction

The use of alkaline phosphatase (ALP) as a biomarker in some diseases including hepatitis, obstructive jaundice, osteoblastic bone cancer, and osteomalacia is important in clinical diagnosis. Furthermore, ALP activity detection is an essential hot topic in environmental monitoring, biomedical research, and other research fields. In this study, a novel "signal-on" photoelectrochemical (PEC) biosensor based on the ALP-catalyzed phosphorylation reaction was designed to sensitively detect ALP activity. In this design, ascorbic acid-an electron donor-was catalytically produced by ALP from l-ascorbic acid 2-phosphate trisodium salt in situ, which results in an increased photocurrent response signal. For immobilizing the ALP on the electrode surface, poly diallyl dimethyl ammonium chloride was used for the conjugation of ALP, and titanium dioxide (TiO₂)-a photoactive material-and graphite-like carbon nitride (g-C₃N₄) nanocomposites were prepared and characterized. TiO₂ attached on g-C₃N₄ plays an important role for the biosensing purpose due to their good biocompatibility and chemical/thermal stability, while g-C₃N₄ provides the PEC response signal. Furthermore, the prepared TiO₂/g-C₃N₄ nanocomposites can effectively suppress electron-hole recombinations, improve the excitation conversion efficiency, and make the best use of solar energy. The PEC biosensor for ALP activity detection displays a detection limit of 0.03 U L^-1 (S/N = 3), which offers a new route for the ALP activity assay in human serum samples.

Exciton-Plasmon Interaction between AuNPs/Graphene Nanohybrids and CdS Quantum Dots/TiO2 for Photoelectrochemical Aptasensing of Prostate-Specific Antigen

A competitive-displacement reaction strategy based on target-induced dissociation of gold nanoparticle coated graphene nanosheet (AuNPs/GN) from CdS quantum dot functionalized mesoporous titanium dioxide (CdS QDs/TiO₂) was designed for the sensitive photoelectrochemical (PEC) aptasensing of prostate-specific antigen (PSA) through the exciton-plasmon interaction (EPI) between CdS QDs and AuNPs. To construct such an aptasensing system, capture DNA was initially conjugated covalently onto CdS QDs/TiO₂-modified electrode, and then AuNPs/GN-labeled PSA aptamer was bound onto biofunctionalized CdS QDs/TiO₂ via hybridization chain reaction of partial bases with capture DNA. Introduction of AuNPs/GN efficiently quenched the photocurrent of CdS QDs/TiO₂ thanks to energy transfer. Upon addition of target PSA, the sandwiched aptamer between CdS QDs/TiO₂ and AuNPs/GN reacted with the analyte analyte, thus resulting in the dissociation of AuNPs/GN from the CdS QDs/TiO₂ to increase the photocurrent. Under optimum conditions, the aptasensing platform exhibited a high sensitivity for PSA detection within a dynamic linear range of 1.0 pg/mL to 8.0 ng/mL at a low limitat of detection of 0.52 pg/mL. The interparticle distance of exciton-plasmon interaction and contents of AuNPs corresponding to EPI effect in this system were also studied. Good selectivity and high reproducibility were obtained for the analysis of target PSA. Importantly, the accuracy and matrix effect of PEC aptasensor was evaluated for the determination of human serum specimens and newborn calf serum-diluted PSA standards, giving a well-matched result with the referenced PSA ELISA kit.

An ultrasensitive "on-off-on" photoelectrochemical aptasensor based on signal amplification of a fullerene/CdTe quantum dots sensitized structure and efficient quenching by manganese porphyrin

In this work, an ultrasensitive "on-off-on" photoelectrochemical (PEC) aptasensor was proposed based on the signal amplification of a fullerene/CdTe quantum dot (nano-C60/CdTe QDs) sensitized structure and efficient signal quenching of nano-C60/CdTe QDs by a manganese porphyrin (MnPP).

A review on visible-light induced photoelectrochemical sensors based on CdS nanoparticles

Discovering the distinctive photophysical properties of semiconductor nanoparticles (NPs) has made these a popular subject in recent advances in nanotechnology-related analytical methods.

Nitrogen-Doped Porous Carbon-ZnO Nanopolyhedra Derived from ZIF-8: New Materials for Photoelectrochemical Biosensors

Herein, novel photoactive materials, nitrogen-doped porous carbon-ZnO (NPC-ZnO) nanopolyhedra, were prepared by direct carbonization of zeolitic imidazolate framework (ZIF)-8 nanopolyhedra in a nitrogen atmosphere. The morphology, structure, and photoelectrochemical (PEC) properties were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, nitrogen adsorption-desorption method, and PEC methods. The results showed that the obtained NPC-ZnO nanopolyhedra had a rhombic dodecahedron morphology with uniform particle size of about 100 nm and a high surface area of 609.2 m² g^-1. Under visible-light irradiation, the NPC-ZnO nanopolyhedra showed better PEC performance than ZnO nanorod and the ZIF-8 nanopolyhedra in aqueous media with dissolved oxygen and ascorbic acid. Taking alkaline phosphatase (ALP) as a model, a NPC-ZnO nanopolyhedra-based PEC sensor was developed and showed good performance for ALP assay with a wide linear response range from 2 to 1500 U L^-1 and a low detection limit of 1.7 U L^-1. Moreover, the PEC sensor possessed acceptable selectivity, reproducibility, and stability. The prepared NPC-ZnO nanopolyhedra provide a new photoactive material for the construction of PEC sensors and may have promising applications in PEC assay of heavy metal ions, organic pollutants, and biomolecules.

Near-Infrared-to-Ultraviolet Light-Mediated Photoelectrochemical Aptasensing Platform for Cancer Biomarker Based on Core-Shell NaYF4:Yb,Tm@TiO2 Upconversion Microrods

Titanium dioxide (TiO₂; as a potential photosensitizer) has good photocurrent performance and chemical stability but often exhibits low utilization efficiency under ultraviolet (UV) region excitation. Herein, we devised a near-infrared light-to-UV light-mediated photoelectrochemical (PEC) aptasensing platform for the sensitive detection of carcinoembryonic antigen (CEA) based on core-shell NaYF₄:Yb,Tm@TiO₂ upconversion microrods by coupling with target-triggered rolling circle amplification (RCA). The upconversion microrods synthesized through the hydrothermal reaction could act as a photosensing platform to convert the near-infrared (near-IR) excitation into UV emission for generation of photoinduced electrons. The target analyte was determined on a functional magnetic bead by using the corresponding aptamers with a sandwich-type assay format. Upon target CEA introduction, a complex was first formed between capture aptamer-1-conjugated magnetic bead (Apt1-MB) and aptamer-2-primer DNA (Apt2-pDNA). Thereafter, the carried primer DNA by the aptamer-2 paired with linear padlock DNA to trigger the RCA reaction. The guanine (G)-rich product by RCA reaction was cleaved by exonuclease I and exonuclease III (Exos I/III), thereby resulting in the formation of numerous individual guanine bases to enhance the photocurrent of core-shell NaYF₄:Yb,Tm@TiO₂ upconversion microrods under near-IR illumination (980 nm). Under optimal conditions, the near-IR light-mediated PEC aptasensing system could exhibit good photoelectrochemical response toward target CEA and allowed for the detection of target CEA as low as 3.6 pg mL^-1. High reproducibility and good accuracy were achieved for analysis of human serum specimens. Importantly, the near-IR-activated PEC aptasensing scheme provides a promising platform for ultrasensitive detection of other biomolecules.

Carbon Dots/g-C3N4 Nanoheterostructures-Based Signal-Generation Tags for Photoelectrochemical Immunoassay of Cancer Biomarkers Coupling with Copper Nanoclusters

A class of 0-dimensional/2-dimensional (0D/2D) nanoheterostructures based on carbon quantum dots (CQDs) and graphitic carbon nitride (g-C₃N₄) was designed as the signal-generation tags for the sensitive photoelectrochemical (PEC) immunoassay of prostate-specific antigen (PSA) coupling with the copper nanoclusters (CuNCs). Combination of CQDs with g-C₃N₄ promoted the photoexcited electron/hole separation and largely increased the photocurrents of the nanoheterostructures. Initially, a sandwich-type immunoreaction was carried out on monoclonal anti-PSA antibody-coated microplate by using PSA aptamer linked with CuNCs as the tracer. Accompanying the immunocomplex, the carried CuNCs were dissolved under acidic conditions. The as-released copper ions from the CuNCs could be captured onto the CQDs/g-C₃N₄ nanoheterostructures via the amino-group on the CQD surface as well as the -NH_x (x = 1, 2, 3) of g-C₃N₄ nanosheets. The strong coordination of the Lewis basic sites on the CQDs/g-C₃N₄ with Cu²⁺ decreased the photocurrent of the nanoheterostructures. Under optimal conditions, CQDs/g-C₃N₄ nanoheterostructures displayed good photocurrent responses for the detection of PSA within the dynamic linear range of 0.02-100 ng mL^-1 and a limit of detection (LOD) of 5.0 pg mL^-1. This method was also evaluated for quantitative screening of human PSA serum specimens by using the referenced electrochemiluminescent enzyme-linked immunoassay (ECL-ELIA) and gave good matched results between two methods. Additionally, this system was beneficial to explore the charge-separation and photoinduced electron transfer mechanism in the photoelectrochemical sensing protocols.

Reduced graphene oxide/BiFeO3 nanohybrids-based signal-on photoelectrochemical sensing system for prostate-specific antigen detection coupling with magnetic microfluidic device

A novel magnetic controlled photoelectrochemical (PEC) sensing system was designed for sensitive detection of prostate-specific antigen (PSA) using reduced graphene oxide-functionalized BiFeO₃ (rGO-BiFeO₃) as the photoactive material and target-triggered hybridization chain reaction (HCR) for signal amplification. Remarkably enhanced PEC performance could be obtained by using rGO-BiFeO₃ as the photoelectrode material due to its accelerated charge transfer and improved the visible light absorption. Additionally, efficient and simple operation could be achieved by introducing magnetic controlled flow-through device. The assay mainly involved in anchor DNA-conjugated magnetic bead (MB-aDNA), PSA aptamer/trigger DNA (Apt-tDNA) and two glucose oxidase-labeled hairpins (H1-GOx and H2-GOx). Upon addition of target PSA, the analyte initially reacted with the aptamer to release the trigger DNA, which partially hybridized with the anchor DNA on the MB. Thereafter, the unpaired trigger DNA on the MB opened the hairpin DNA structures in sequence and propagated a chain reaction of hybridization events between two alternating hairpins to form a long nicked double-helix with numerous GOx enzymes on it. Subsequently, the enzymatic product (H₂O₂) generated and consumed the photo-excited electrons from rGO-BiFeO₃ under visible light irradiation to enhance the photocurrent. Under optimal conditions, the magnetic controlled PEC sensing system exhibited good photocurrent responses toward target PSA within the linear range of 0.001 - 100ng/mL with a detection limit of 0.31pg/mL. Moreover, favorable selectivity, good stability and satisfactory accuracy were obtained. The excellent analytical performance suggested that the rGO-BiFeO₃-based PEC sensing platform could be a promising tool for sensitive, efficient and low cost detection of PSA in disease diagnostics.