2D Z-scheme ZnIn2S4/g-C3N4 heterojunction based on photoelectrochemical immunosensor with enhanced carrier separation for sensitive detection of CEA

Constructing BiOI@Nv/g-C3N4 with S-scheme heterojunction for enhanced photoelectrochemical performances towards highly sensitive and selective detection of trace chlorpyrifos

Chlorpyrifos, one of the organophosphorus pesticide commonly used in the environment, may bring about an irreversible harm such as lung cancer to human body. Photoelectrochemical (PEC) detection techniques based on g-C3N4 for sensing chlorpyrifos have attracted increasing attentions, but impeded by several inherent constraints such as a limit of active sites and carriers transfer. To conquer these challenges, a photoelectrochemical sensor of BiOI@Nv/g-C3N4 with a step scheme heterojunction was thereby proposed for the sensitive and selective detection of trace chlorpyrifos. Herein, the created N vacancies facilitated the migration of photo-electrons from BiOI to recombine with the holes of Nv/g-C3N4 under light irradiation. A powerful oriented built-in electric field was established directing from Nv/g-C3N4 to BiOI. The photocurrent intensity of the as-prepared sensor exhibited over 7.6 times higher than that of pure g-C3N4, showing a well PEC performance. High selectivity of the developed sensor was attributed to the specific interaction between Bi sites of the developed composites and the S, N atoms in chlorpyrifos. Such sensitive and steady PEC sensor exhibited a linear detection range from 0.01 to 20 ppb with a detection limit of 0.004 ppb. Further, the sensor displayed reliable performance when applied to real river water and soil samples, achieving nice recovery rates. Unlike traditional PEC sensor, this one was prepared into S-scheme heterojunction by creating a N defect-induced driving force based on the altered built-in electric field. The work not only provides experimental evidences but also advances the fundamental theories so as to offer a robust g-C3N4-based PEC platform for environmental analysis.

Bi2WO6-labeled antibody induced photocurrent polarity switching of ZnIn2S4-based photoelectrochemical immunosensor for the highly sensitive detection of carcinoembryonic antigen

Developing effective detection methods for disease markers is essential for clinical diagnosis and therapeutic prognostic assessment. In this work, hollow Bi-doped Bi2WO6 was synthesized by using carbon sphere as template, and then it was used as the label of secondary antibody to induce current polarity reversal in the flower shaped ZnIn2S4 based photoelectrochemical (PEC) immunosensor. Thus the easily disturbed anodic photocurrent was converted to cathodic photocurrent with better resistance to interference from reducing substances. Furthermore, the reversal of polarity made the influence of background signal decrease, the detection range become wide, and the sensitivity increase. The introduced poly(dopamine) film could inhibit the anodic photocurrent of ZnIn2S4 in addition to fixing antibody, assisting Bi2WO6 in inducing subsequent current polarity conversion. Under the optimized conditions, the linear response range of the sandwich immunosensor was as wide as 0.0005-20.0 ng/mL, with a quite low limit of 0.18 pg/mL for the assay of model molecule carcinoembryonic antigen. The PEC sensor also exhibited satisfying selectivity and stability. It was applied to detect serum samples and satisfactory results were achieved.

An "on-off-on" photoelectrochemical aptasensor using CoO as a signal label for T-2 toxin detection

T-2 toxin, a mycotoxin commonly found in food, is recognized as one of the most harmful contaminants. Herein, a sensitive photoelectrochemical (PEC) aptasensor based on an "on-off-on" signal response strategy was developed for T-2 detection using WO3/CdIn2S4 as a photoanode. The sensitization of WO3 with CdIn2S4 significantly enhanced the photocurrent, leading to the initial "signal-on" state. As a signal label of probe DNA (pDNA), CoO significantly inhibited the photocurrent response of WO3/CdIn2S4 ("signal-off" state), enhancing the signal recovery space and improving the detection sensitivity. T-2 toxin is preferentially bound to aDNA, releasing the CoO-pDNA complex from the electrode, realizing the "signal-on" state again. This signal switching mechanism enabled a broad detection range from 1 fg mL-1 to 1 μg mL-1 with an ultralow detection limit of 0.434 fg mL-1 (S/N = 3), while the sensor exhibited excellent reproducibility, stability and selectivity. This platform not only provided a robust analytical tool for T-2 toxin detection in food safety but also established a generalizable sensing paradigm adaptable to other mycotoxins by replacing the recognition element.

Cryogenically Induced Highly Ordered Single-Strand DNA-Modified Magnetic Nanoprobes for Rapid and Ultrasensitive Bioanalysis

The development of highly sensitive detection methods for bioanalysis is crucial for early disease diagnosis. Electrochemical biosensing technology offers unique advantages in this area due to its rapid response, high sensitivity, and low cost. However, achieving efficient and rapid transfer of signaling molecules to the electrode interface to facilitate effective interaction between signal molecules and the sensing surface remains a critical challenge for ultrasensitive electrochemical detection. In this study, we discovered that single-stranded DNA-modified magnetic nanoprobes (signal probe A) subjected to cryogenic treatment can rapidly form an orderly monolayer at the electrode interface under an external magnetic field, while this phenomenon was not observed with double-stranded DNA-modified magnetic nanoprobes (signal probe B). Building on this finding, we developed a signal probe with a protective complementary strand (signal probe B) that, upon interaction with target molecules, is converted into signal probe A. This transformation, combined with cryogenic treatment, enables the ultrasensitive detection of target molecules. Using miRNA-21 and a carcinoembryonic antigen (CEA) as model targets, we optimized the detection conditions, achieving a detection limit as low as 3.4 aM for miRNA-21 and 0.28 fg/mL for CEA with excellent versatility. In summary, this study introduces a highly efficient, rapid, enzyme-free, and environmentally friendly electrochemical signal amplification strategy. This approach not only provides an innovative solution for the ultrasensitive bioanalysis but also offers new insights into enhancing signal molecule-sensor interface interactions in electrochemical biosensors.

A "signal-on" photoelectrochemical sensor based on hierarchical titanium dioxide nanowires/microflowers decorated graphite-like carbon nitride quantum dots for glutathione detection

Glutathione (GSH) is a bioactive tripeptide with important physiological functions in animals, plants, and microorganisms. GSH participates in various biochemical reactions in vivo and is known for its antioxidant, anti-allergy, and detoxification properties. This study introduces an innovative photoelectrochemical (PEC) method for GSH detection, leveraging a fluorine-doped tin oxide (FTO) electrode enhanced by TiO2 nanoflowers and graphitic carbon nitride quantum dots (g-CNQDs). This design formed a type-II heterojunction, which facilitated efficient charge separation and transport. Furthermore, incorporating TiO2 nanoflowers increases the surface area, while adding g-CNQDs led to a narrowing of the semiconductor bandgap. The fabricated electrode exhibits highly attractive photo-electrocatalytic activity towards GSH detection in neutral media at a low potential bias. The developed PEC sensor demonstrates a wide linear range of 1.0 × 10-13 to 5 × 10-5 mol L-1, a low detection limit of 5.0 fmol L-1, and high sensitivity. These remarkable analytical characteristics highlight the potential of this PEC platform for sensitive and selective GSH detection in various biomedical and environmental applications.

Flower-like tailored carbon nitride oligomer as an excellent aggregation-induced electrochemiluminescence emitter for sensitive immunoassay of neuron-specific enolase via dual quenching by bimetallic phenolic networks

The adjustment of the electrochemiluminescence (ECL) of polymeric carbon nitride (C3N4) is essential for its application in sensitive immunoassays. However, such modification through aggregation-induced emission (AIE) has not yet been reported. Herein, aggregation-induced ECL in C3N4 oligomer (CNO) was induced through the introduction of a rotatable imine moiety, with the resulting material exhibiting excellent performance in the targeted immunodetection of neuron-specific enolase. Phenyl-modified CNO was synthesized through one-step pyrolysis at a reduced temperature. The rotatable benzene ring and triazine group formed a dynamic structure, which exhibited strong aggregation in water-doped solvents. compared to unmodified graphitic C3N4, CNO demonstrated higher intrinsic ECL efficiency and more readily accessible ECL signals. AIE inducing polymerization was conducted via nanoprecipitation, and the resulting CNO micro-flowers were employed as a sensing platform. A CNO-based sensor was prepared by combining CNO micro-flowers with copper-based bimetallic phenolic network nanoparticles as a quencher. Sensitive signal quenching was achieved owing to the electron transfer of Cu2+ and antioxidation properties of polyphenolic structures. The prepared sandwich-type immunosensor for neuron-specific enolase showed a limit of detection of 0.12 pg/mL in the detection range of 0.001-100 ng/mL. This study presents an effective strategy for the ECL signal amplification of C3N4, which is conducive to fundamental research in ECL and the application of the proposed sensor in the early diagnosis of diseases.

Research progress of photoelectrochemical sensors in food detection

Food is the basic of the people, security is the basic of the food. As the quality of life improves, food safety has emerged as a global concern, making the development of simple, rapid, and efficient food safety detection methods critically important. Photoelectrochemical (PEC) sensors are a novel class of sensors developed in recent years that integrate photoelectric technology with biosensing. Owing to their high sensitivity, simple design, low cost, and ease of miniaturization, PEC sensors have found widespread applications in food detection, bioanalysis, clinical diagnostics, and environmental protection. This paper reviews the development of PEC sensors, the basic principles of PEC sensor detection, and the electron transport pathways of semiconductor materials in PEC sensors. It focuses on how photoelectroactive materials and related signal amplification strategies can improve the detection performance of the sensors, as well as the latest research advances of PEC sensors in the detection of food toxins. Finally, the challenges and future trends of PEC sensors in food safety detection are discussed.

In-situ nanozyme catalytic amplification coupled with a universal antibody orientation strategy based electrochemical immunosensor for AD-related biomarker

An in-situ nanozyme signal tag combined with a DNA-mediated universal antibody-oriented strategy was proposed to establish a high-performance immunosensing platform for Alzheimer's disease (AD)-related biomarker detection. Briefly, a Zr-based metal-organic framework (MOF) with peroxidase (POD)-like activity was synthesized to encapsulating the electroactive molecule methylene blue (MB), and subsequently modified with a layer of gold nanoparticles on its surface. This led to the creation of double POD-like activity nanozymes surrounding the MB molecule to form a nanozyme signal tag. A large number of hydroxyl radicals were generated by the nanozyme signal tag with the help of H2O2, which catalyzed MB molecules in situ to achieve efficient signal amplification. Subsequently, a DNA-aptamer-mediated universal antibody-oriented strategy was proposed to enhance the binding efficiency for the antigen (target). Meanwhile, a poly adenine was incorporated at the end of the aptamer, facilitating binding to the gold electrode and providing anti-fouling properties due to the hydrophilicity of the phosphate group. Under optimal conditions, this platform was successfully employed for highly sensitive detection of AD-associated tau protein and BACE1, achieving limits of detection with concentrations of 3.34 fg/mL and 1.67 fg/mL, respectively. It is worth mentioning that in the tau immunosensing mode, 20 clinical samples from volunteers of varying ages were analyzed, revealing significantly higher tau expression levels in the blood samples of elderly volunteers compared to young volunteers. This suggests that the developed strategy holds great promise for early AD diagnosis.

A photoelectrochemical sensor based on In2S3/AgInS2 in situ Z-type heterojunction with "photo-modulated interface charge" for sensitive detection of Programmed Death-Ligand 1

The construction of heterostructure photoelectrodes can enhance the performance of photoelectrochemical (PEC) sensors. However, it is still a critical challenge to achieve efficient transfer of interface carriers. In this paper, we propose a strategy of "photo-modulated interface charge" to design a PEC sensor based on a hollow hexagonal tubular In2S3/AgInS2 in situ Z-type heterojunction for the susceptible detection of Programmed Death-ligand 1 (PD-L1). The hollow structured In2S3/AgInS2 is ingeniously synthesized employing indium-sourced MIL-68 as a sacrificial template and in situ cation exchange technique. This composite material has close contact interfaces due to in situ growth, which facilitates the spontaneous establishment of a robust and stable built-in electric field between the interfaces. Moreover, the inner cavity structure promotes multiple light refractions and scatterings, significantly enhancing light trapping capability. Under the influence of both light irradiation and electric field force, the migration direction of the interfacial charge is reversed, forming a Z-transfer path, which effectively delays the compounding of the electron-hole pairs (e-/h+) and further improves the sensitivity of the sensor. The minimum detection threshold of the PEC sensor is 26.58 fg/mL, and the feasibility of real samples is investigated, providing new insights for early diagnosis and prognostic treatment of diseases.

Cu2O-Mediated Heterojunction Conversion from Dual Type II to Dual Z-Scheme: Its Application in Photoelectric-Colorimetric Dual-Mode Detection of Fat Mass and Obesity-Associated (FTO) Protein

Although the construction of heterojunction has been used in photoelectrochemical (PEC) biosensors, their potential for tunable optical properties has not been deeply explored. Based on the fact that a type-II heterojunction and Z-scheme heterojunction have the same energy band structure, effective alteration of the electron transfer pathway has been achieved by introducing unique photoactive materials into the system and exploiting the interactions between the photomaterials. Based on this, we reported a novel polarity-switchable dual-mode sensor for fat mass and obesity-associated (FTO) protein analysis. Specifically, the MgIn2S4/Bi2MoO6/Bi2S3 dual type-II heterojunction was used as the sensing interface in concert with the rolling circle amplification, CRISPR/Cas12, and terminal DNA transfer enzyme multiamplification strategies, and finally, Cu2O was captured at the sensing interface. Due to the matched energy band, the introduction of Cu2O effectively changed the electron transfer pathway and realized the conversion from a dual type-II heterojunction to a dual Z-scheme heterojunction. It caused the switch of the photocurrent from the anode to the cathode. The developed PEC method showed high sensitivity and selectivity for FTO protein detection in the range of 0.0005-500 μg/L. In addition, based on the peroxidase-like activity of Cu2O to catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine by H2O2, the electrode system also achieved the colorimetric detection of FTO protein using the naked eye with the change of the color of the detection solution from colorless to blue. The detection range was from 0.05 to 500 μg/L. This work developed a photoelectrochemical-colorimetric biosensing platform with consciously designed semiconductor structures, revealing the potential of semiconductor-structured transformations in future sensing fields.

Quenching study of Cu2S-MPA/NGODs composites in electrochemiluminescence detection by modulating resonance energy transfer and adsorption process

This study explores the principles of resonance energy transfer and adsorption modulation using composites of Cu2S-MPA/NGODs. These composites can efficiently control the quenching process of electrochemiluminescence (ECL). Mercaptopropionic acid (MPA) was added during the synthesis of Cu2S-MPA to enhance its attachment to nitrogen-doped graphene quantum dots (NGODs). The UV absorption peaks of NGODs coincided with the emission peaks of luminol ECL, enabling resonance energy transfer and enhancing the quenching capability of Cu2S-MPA. Meanwhile, there is another quenching strategy. When the readily reducible Cu+ ions underwent partial reduction to Cu when they were bound to NGODs. This weakened the electrocatalytic effect on reactive oxygen species (ROS) and had a detrimental impact on electron transfer. Under optimal conditions, the immunosensor ECL intensity decreased linearly with the logarithm of carcinoembryonic antigen (CEA) concentration in the range of 0.00001-40 ng/mL, with a detection limit of 0.269 fg/mL. The sensor was effectively utilized for the identification of CEA in actual serum samples.

A Photoelectrochemical Biosensor Mediated by CRISPR/Cas13a for Direct and Specific Detection of MiRNA-21

Direct detection of miRNA is currently limited by the complex amplification and reverse transcription processes of existing methods, leading to low sensitivity and high operational demands. Herein, we developed a CRISPR/Cas13a-mediated photoelectrochemical (PEC) biosensing platform for direct and sensitive detection of miRNA-21. The direct and specific recognition of target miRNA-21 by crRNA-21 eliminates the need for pre-amplification and reverse transcription of miRNA-21, thereby preventing signal distortion and enhancing the sensitivity and precision of target detection. When crRNA-21 binds to miRNA-21, it activates the trans-cleavage activity of CRISPR/Cas13a, leading to the non-specific cleavage of biotin-modified DNA with uracil bases (biotin-rU-DNA). This cleavage prevents the biotin-rU-DNA from being immobilized on the electrode surface. As a result, streptavidin cannot attach to the electrode via specific biotin binding, reducing spatial resistance and causing a positively correlated increase in the photocurrent response. This Cas-PEC biosensor has good analytical capabilities, linear responses between 10 fM and 10 nM, a minimum detection limit of 9 fM, and an excellent recovery rate in the analysis of real human serum samples. This work presented an innovative solution for detecting other biomarkers in bioanalysis and clinical diagnostics.

Cascading CRISPR/Cas and Nanozyme for Enhanced Organic Photoelectrochemical Transistor Detection with Triple Signal Amplification

Innovative signal amplification and transduction play pivotal roles in bioanalysis. Herein, cascading CRISPR/Cas and the nanozyme are integrated with electronic amplification in an organic photoelectrochemical transistor (OPECT) to enable triple signal amplification, which is exemplified by the miRNA-triggered CRISPR/Cas13a system and polyoxometalate nanozyme for OPECT detection of miRNA-21. The CRISPR/Cas13a-enabled release of glucose oxidase could synergize with peroxidase-like SiW12 to induce catalytic precipitation on the photogate, inhibiting the interfacial mass transfer and thus the significant suppression of the channel current. The as-developed OPECT sensor demonstrates good sensitivity and selectivity for miRNA-21 detection, with a linear range from 1 fM to 10 nM and an ultralow detection limit of 0.53 fM. This study features the integration of bio- and nanoenzyme cascade and electronic triple signal amplification for OPECT detection.

Organic polymer/inorganic heterostructure coupled with efficient allosteric bicycle strand displacement for photochemical sensing

In this work, a high-performance conjugated microporous polymer (CMP) decorated with BiOBr (Tr(PhXOD)3-CMP/BiOBr) is synthesized to application in construction of ultrasensitive photoelectrochemical (PEC) biosensor for sensing miRNA-122, by firstly coupling with efficient clip toehold-mediated allosteric bicycle strand displacement (ABSD). Notably, the Tr(PhXOD)3-CMP/BiOBr not only owns self-enhanced D-A-D structure that extremely shortens migration distance of photo-generated electron, but also forms Z-type heterostructure for accelerating electron-hole separation, thereby significantly enhancing the photocurrent with 10-fold higher than commonly used methods. Meanwhile, the clip toehold-mediated ABSD based on ternary linkage structure transformation avoids the attrition of invading strand, endowing the conservation of high concentration for undergoing rapid reaction with high-efficiency DNA amplification, which dramatically improves reaction time and superior target conversion. The experimental results indicate that proposed PEC biosensor had a high sensitivity to miRNA-122 with a detection limit of 0.49 fM, which provides a newly organic/inorganic photosensitive nanomaterials and efficient DNA strand displacement in bioanalytical and early clinical disease diagnosis.

CuInS2/Red Phosphorus Nanosheet Interleaved Heterostructures with Improved Interfacial Charge Transfer for Photoelectrochemical Aptasensing

Accelerating the migration of interfacial carriers in heterojunctions is crucial for achieving highly sensitive photoelectrochemical (PEC) sensing. In this study, we developed three-dimensional (3D)/two-dimensional (2D) CuInS2/red phosphorus nanosheet (CuInS2/RP NS) n-n heterojunction functional materials with enhanced interfacial charge transfer capabilities for PEC sensing. The 3D CuInS2 serves as a conductive layer, providing excellent electronic conductivity and superior electron absorption and transport properties. In contrast, the ultrathin RP NS acts as a transport layer that enhances carrier mobility. The 3D/2D heterojunction ensures a large interface contact surface, shortening the carrier transport distance. A well-aligned band position generates a substantial built-in electric field, providing a significant driving force for efficient carrier separation and migration, thereby improving response sensitivity. A PEC aptamer sensor was constructed based on the synthesized heterostructure for ciprofloxacin detection. The detection limit of the CuInS2/RP NS aptamer sensor for ciprofloxacin is 2.03 × 10-15 mg·mL-1, with a linear range from 1.0 × 10-14 to 1.0 × 10-5 mg·mL-1. This work presents a strategy for enhancing the photoelectric response by modulating the interface structure of heterojunctions, thereby opening new prospects for the application of highly sensitive PEC sensors in antibiotic detection.

Carbon quantum dots(CQDs)-sensitized CdS/CuInS2 heterojunction as a photoelectrochemical biosensing platform for highly sensitive detection of prostate-specific antigen

Sensitive and quantitative detection of prostate-specific antigen (PSA) has been determined to be indispensable for clinical diagnostics of prostate cancer, whereas such detection is quite challenging due to the extremely low concentration of biomarkers in human serum samples. In this study, a photoelectrochemical (PEC) sensor was effectively developed for the high-sensitivity analysis of prostate-specific antigen (PSA) using a signal amplification method utilizing sensitized carbon quantum dots (CQDs). In this experiment, cadmium sulfide quantum dots were employed as the substrate materials, and indium copper sulfide quantum dots were loaded on their surfaces. Moreover, the efficient matching of energy levels in these two materials contributed to the generation of photocurrents. The aforementioned heterojunction semiconductor QDs were thus combined with CQDs to produce CQDs on their surfaces. As a result of the presence of CQDs, the ability of heterojunction materials to absorb light was remarkably enhanced, increasing the photocurrent by over ten times. Consequently, in this study, CQDs were combined with PEC sensors, and the developed PEC biosensors exhibited excellent optical performance, sensitivity, repeatability, and stability. The results obtained from the analysis of actual samples were satisfactory and have promising application prospects.

Progress of charge carrier dynamics and regulation strategies in 2D CxNy-based heterojunctions

Two-dimensional carbon nitrides (CxNy) have gained significant attention in various fields including hydrogen energy development, environmental remediation, optoelectronic devices, and energy storage owing to their extensive surface area, abundant raw materials, high chemical stability, and distinctive physical and chemical characteristics. One effective approach to address the challenges of limited visible light utilization and elevated carrier recombination rates is to establish heterojunctions for CxNy-based single materials (e.g. C2N3, g-C3N4, C3N4, C4N3, C2N, and C3N). The carrier generation, migration, and recombination of heterojunctions with different band alignments have been analyzed starting from the application of CxNy with metal oxides, transition metal sulfides (selenides), conductive carbon, and Cx'Ny' heterojunctions. Additionally, we have explored diverse strategies to enhance heterojunction performance from the perspective of carrier dynamics. In conclusion, we present some overarching observations and insights into the challenges and opportunities associated with the development of advanced CxNy-based heterojunctions.