Versatile Photoelectrochemical Biosensing for Hg2+ and Aflatoxin B1 Based on Enhanced Photocurrent of AgInS2 Quantum Dot-DNA Nanowires Sensitizing NPC-ZnO Nanopolyhedra

Photoelectrochemical analysis of Pb2+ based on Au@PTCA Schottky junction with Pb2+-G quadruplex structure

Herein, a novel photoelectrochemical (PEC) aptasensor using gold nanoparticles@3,4,9,10-perylene tetracarboxylic (Au@PTCA) Schottky junction as the effective optoelectronic material and lead ion (Pb2+)-G quadruplex structure as the efficient quencher was constructed for the detection of Pb2+ with high sensitivity and excellent selectivity. Au@PTCA Schottky junction, which was proposed by the in situ reduction of Au NPs on the PTCA surface, exhibited a strong unidirectional conductivity, which could generate a significantly enhanced PEC signal compared with the pure PTCA. The Pb2+-G quadruplex structure with a large spatial hindrance effect was formed when the target Pb2+ was present owing to the occurrence of the specific recognition between Pb2+ and its aptamer S1. The formation of a Pb2+-G quadruplex structure effectively quenched the initial signal generated by the Au@PTCA Schottky junction, which was derived from restricted electron transport and light transmission. The obtained prominently decreased PEC signal could achieve the quantitative detection of Pb2+ from 0.5 pM to 500 nM, with a low detection limit of 0.17 pM. The preparation time of this PEC aptasensor was 13 h, and the time for PEC measurement depended on the illumination time, which switched off-on-off for 10 s-20 s-10 s. The study proposed here with high sensitivity and excellent selectivity for Pb2+ analysis offered a novel and reliable tool for environmental monitoring related to heavy metal ions.

A multi-modal biosensing platform based on Ag-ZnIn2S4@Ag-Pt nanosignal probe-sensitized UiO-66 for ultra-sensitive detection of penicillin

We designed a multi-modal biosensing platform for versatile detection of penicillin based on a unique Ag-ZnIn2S4@Ag-Pt signal probe-sensitized UiO-66 metal-organic framework. Firstly, a large number of Ag-ZnIn2S4 quantum dots (AZIS QDs) were attached to Ag-Pt NPs, preparing a new multi-signal probe AZIS QDs@Ag-Pt NPs with excellent photoelectrochemistry (PEC), electrochemiluminescence (ECL), and fluorescence (FL) signals. Moreover, the AZIS QDs@Ag-Pt NPs signal probe can well match the energy level of UiO-66 metal-organic framework (MOF) with good photoelectric property, which can reverse the PEC current of UiO-66 to reduce false positives in detection. When penicillin was present, it bound to its aptamer to release the multifunctional signal probes, which can generate PEC, ECL, and PL signals, thus realizing ultrasensitive detection of penicillin by multi-signals. This work creates a novel three-signal QDs probe, which makes a great contribution to multi-mode photoelectric sensing analysis. The LOD of this work (3.48 fg·mL-1) was much lower than the MRLs (Maximum Residue Levels) established by the EU (4 ng·mL-1). The newly developed multi-mode biosensor has good practical application values in various biological detection, food assay, and early disease diagnosis.

Electrochemical/photoelectrochemical dual-mode aptasensor for sensitive aflatoxin B1 assay based on distance-modulation strategy using Au NPs/PCZIF-8-ZnO as sensing substrate

Aflatoxin B1 (AFB1), a hepatotoxic and carcinogenic food contaminant, is commonly found in agricultural food. Herein, Au NPs anchored ZIF-8-derived porous carbon-ZnO (Au NPs/PCZIF-8-ZnO) was firstly synthesized to act as the sensing substrate. Then, a ratiometric electrochemical (EC) and "off-on" photoelectrochemical (PEC) dual-mode paper-based aptasensor was presented for AFB1 detection based on a distance-modulation sensing strategy. The independent signal transduction mechanisms and output mode not only broaden the dynamic detection range but also provide a self-verification to assay results, improving the sensitivity and reliability. The wide detection ranges of 0.1 pg/mL-100 ng/mL (EC mode) and 0.02 pg/mL-100 ng/mL (PEC mode) were obtained using dual-mode aptasensor, with detection limits of 36.7 and 9.3 fg/mL, respectively. The fabricated aptasensor exhibited excellent selectivity, reproducibility and stability. Furthermore, it exhibited good practicability for AFB1 assays in real samples, demonstrating great potential applications for food safety evaluation.

A signal-on photoelectrochemical aptasensor based on ferrocene labeled triple helix DNA molecular switch for detection of antibiotic amoxicillin

A sensitive signal-on photoelectrochemical aptasensor for antibiotic determination was constructed based on the energy level matching between ferrocene and CuInS2. P-type CuInS2 microflower was complexed with reduced graphene oxide (CuInS2/rGO) to get photocathode current with good photoelectric conversion efficiency and stability. Then, hairpin DNA (HP) was covalently bonded to the electrode surface. A triple helix DNA (THMS) was used as a molecular switch. After the specific recognition between target and THMS in homogeneous solution, ferrocene labeled probe (Fc-T2) was released. Finally, Fc-T2 was captured by the HP, which leaded the obvious increase of photocurrent for the energy level matching between ferrocene and CuInS2. The increase of the photocurrent signal was proportional to the concentration of target amoxicillin (AMOX), the linear range was 100 fM-100 nM with detection limit of 19.57 fM. Meanwhile, the method has been successfully applied for milk and lake water samples analysis with satisfactory results.

Spatial-Potential-Color-Resolved Bipolar Electrode Electrochemiluminescence Biosensor Using a CuMoOx Electrocatalyst for the Simultaneous Detection and Imaging of Tetracycline and Lincomycin

A spatial-potential-color-resolved bipolar electrode electrochemiluminescence biosensor (BPE-ECL) using a CuMoOx electrocatalyst was constructed for the simultaneous detection and imaging of tetracycline (TET) and lincomycin (LIN). HOF-101 emitted peacock blue light under positive potential scanning, and CdSe quantum dots (QDs) emitted green light under negative potential scanning. CuMoOx could catalyze the electrochemical reduction of H2O2 to greatly increase the Faradic current of BPE and realize the ECL signal amplification. In channel 1, CuMoOx-Aptamer II (TET) probes were introduced into the BPE hole (left groove A) by the dual aptamer sandwich method of TET. During positive potential scanning, the polarity of BPE (left groove A) was negative, resulting in the electrochemical reduction of H2O2 catalyzed by CuMoOx, and the ECL signal of HOF-101 was enhanced for detecting TET. In channel 2, CuMoOx-Aptamer (LIN) probes were adsorbed on the MXene of the driving electrode (DVE) hole (left groove B) by hydrogen-bonding and metal-chelating interactions. LIN bound with its aptamers, causing CuMoOx to fall off. During negative potential scanning, the polarity of DVE (left groove B) was negative and the Faradic current decreased. The ECL signal of CdSe QDs was reduced for detecting LIN. Furthermore, a portable mobile phone imaging platform was built for the colorimetric (CL) detection of TET and LIN. Thus, the multiple mode-resolved detection of TET and LIN could be realized simultaneously with only one potential scan, which greatly improved detection accuracy and efficiency. This study opened a new technology of BPE-ECL sensor application and is expected to shine in microchips and point-of-care testing (POCT).

Amplified Assembly of G-Quadruplex-Decorated DNA Network Nanostructure toward AIE Signaling-Based Sensitive Biosensing

Aggregation-induced emission (AIE) has offered a promising approach for developing low-background fluorescent methods; however, its applications often suffer from complex probe synthesis and poor biocompatibility. Herein, a novel AIE biosensing method for kanamycin antibiotic assays was developed by utilizing a DNA network nanostructure assembled from an aptamer recognition reaction to capture a large number of tetraphenylethylene fluorogen-labeled signal DNA (DTPE) probes. Due to the excellent hydrophilicity of the oligonucleotides, DTPE exhibited excellent water solubility without obvious background signal emission. Based on an ingenious nucleotide design, an abundance of G-quadruplex blocks neighboring the captured DTPE were formed on the DNA nanostructure. Because of the greatly restricted free motion of DTPE by this unique nanostructure, a strong AIE fluorescence signal response was produced to construct the signal transduction strategy. Together with target recycling and rolling circle amplification-based cascade nucleic acid amplification, this method exhibited a wide linear range from 75 fg mL-1 to 1 ng mL-1 and a detection limit down to 24 fg mL-1. The excellent analytical performance and effective manipulation improvement of the method over previous approaches determine its promising potential for various applications.

Recent advances in photoelectrochemical platforms based on porous materials for environmental pollutant detection

Human health and ecology are seriously threatened by harmful environmental contaminants. It is essential to develop efficient and simple methods for their detection. Environmental pollutants can be detected using photoelectrochemical (PEC) detection technologies. The key ingredient in the PEC sensing system is the photoactive material. Due to the unique characteristics, such as a large surface area, enhanced exposure of active sites, and effective mass capture and diffusion, porous materials have been regarded as ideal sensing materials for the construction of PEC sensors. Extensive efforts have been devoted to the development and modification of PEC sensors based on porous materials. However, a review of the relationship between detection performance and the structure of porous materials is still lacking. In this work, we present an overview of PEC sensors based on porous materials. A number of typical porous materials are introduced separately, and their applications in PEC detection of different types of environmental pollutants are also discussed. More importantly, special attention has been paid to how the porous material's structure affects aspects like sensitivity, selectivity, and detection limits of the associated PEC sensor. In addition, future research perspectives in the area of PEC sensors based on porous materials are presented.

HOF-101-based dual-mode biosensor for photoelectrochemical/electrochemiluminescence detection and imaging of oxytetracycline

A unique hydrogen-bonded organic frameworks (HOF-101)-based photoelectrochemical (PEC) and electrochemiluminescence (ECL) dual-mode biosensor using polydopamine nanoparticles (PDAs) as quencher was constructed for ultrasensitive detection and imaging of oxytetracycline (OXY). In particular, HOF-101 was a superior ECL material and can be observed with the naked eye. Furthermore, it also had outstanding PEC signal, so HOF-101 was a new dual-signal material with excellent performance, thus it was explored to realize dual-mode detection. As the main component of natural melanin, PDAs not only had good biocompatibility, but also contained rich functional groups on the surface. Additionally, PDAs had excellent light absorption ability and poor conductivity, which made it the excellent photoquencher. In this work, PDAs were introduced on the surface of HOF-101 to quench its ECL and PEC signals by using the dual-aptamer sandwich method, achieving ultrasensitive detection of antibiotic OXY. Particularly for ECL detection, HOF-101 was firstly used to visually detect OXY. The detection range can reach 0.1 pM-100 nM, and the limit of detection (LOD) can reach 0.04 pM. This work showed a great contribution to the development of new ECL-PEC materials and ECL visualization analysis, which had outstanding application potential in the fields of food safety and biochemical analysis.

A ZnIn2S4@ReS2/AgInS2-based photoelectrochemical aptasensor for the ultrasensitive detection of kanamycin

An ultrasensitive photoelectrochemical (PEC) aptasensor was originally designed by using ZnIn2S4/ReS2 as a photoactive material and AgInS2 as a signal amplifier. The signal amplifier AgInS2 was incubated on the terminal of H-DNA (immobilized on the ZnIn2S4/ReS2/FTO surface), leading to an enhanced photocurrent response. Then, due to the introduction of DNA2, the formation of a double-stranded structure caused AgInS2 to keep away from the electrode surface, and the photocurrent was reduced. In the presence of kanamycin, DNA2 was released from the system due to the competition relationship, and a restored photocurrent response was obtained. The combination of ZnIn2S4/ReS2 and AgInS2 accelerated the electron transfer and enhanced the separation efficiency of photogenerated electron-hole pairs, resulting in an improved performance of the PEC aptasensor, which was capable of accurate and sensitive detection of kanamycin in actual samples.

A metal ion-coordinated DNA probe for sensitive fluorescence detection of metallothionein via a dual nucleic acid amplification strategy

Sensitively monitoring metallothionein (MT), a heavy metal-binding protein with substantial cysteine content, is of significance for evaluating heavy metal poisoning in both humans and animals. Based on a new metal ion-coordinated DNA probe and the heavy metal ion binding capability of MT, as well as the substantial signal enhancement of the hybridization chain reaction (HCR) and rolling circle amplification (RCA), we demonstrate a highly sensitive fluorescence MT detection assay. MT binds the metal ions in the hairpin structured, metal ion-coordinated DNA probe to switch its hairpin structure into ssDNA, which triggers subsequent RCA reactions and HCRs to open plenty of fluorescently quenched signal hairpins to exhibit drastically amplified fluorescence recovery for assaying MT down to 0.58 nM within a dynamic range of 1-320 nM. In addition, the investigation of low contents of MT in diluted human serum by such an assay has also been verified, indicating its promising application potential for diagnosing heavy metal poisoning.

Versatile photoelectrochemical biosensor based on AIS/ZnS QDs sensitized-WSe2 nanoflowers coupled with DNA nanostructure probe for"On-Off"assays of TNF-α and MTase

Herein, a novel multifunctional photoelectrochemical (PEC) biosensor based on AgInS2 (AIS)/ZnS quantum dots (QDs) sensitized-WSe2 nanoflowers and DNA nanostructure signal probe was designed to achieve ultra-sensitive "On-Off" detection of human tumor necrosis factor α (TNF-α) and methylase Dam MTase (MTase). AIS/ZnS QDs as an excellent photosensitive material was found to match WSe2 in energy level for the first time, and the photocurrent signal after sensitization was 65 times that of WSe2 nanoflowers and 17.9 times that of AIS/ZnS QDs. Moreover, abundant AIS/ZnS QDs were loaded on the TiO2 nanoparticles with good conductivity by DNA to fabricate a multifunctional probe, which can not only amplify signal but also specifically recognize target. When target TNF-α was present, the AIS/ZnS QDs signal probe was attached to the WSe2 nanoflowers-modified electrode through binding to aptamer, and the amplified PEC signal was generated for "on" assay of TNF-α. Furthermore, Dam MTase as second target induced methylation of hairpin HDam, so it is cleaved by the endonuclease DpnI, resulting in the shedding of AIS/ZnS QDs signal probe for signal "off" detection of MTase. This work opened a new photosensitized probe and developed a promising PEC biosensor for dual-targets assay. By programming the DNA nanostructure, the biosensor can detect versatile targets in a simple and sensitive method, which has good practical application value in human serum.

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

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

Smart enzyme-free amplification dual-mode self-powered platform designed on two-dimensional networked graphdiyne and DNA nanorods for ultra-sensitive detection of breast cancer biomarkers

Research has shown that microRNAs exhibit regular dysregulation in cancers, making them potential biomarkers for cancer diagnosis. However, achieving specific and sensitive detection of microRNAs has been a challenging task. To address this issue, two-dimensional networked graphdiyne is used to fabricate a self-powered biosensor and establish a new approach for ultra-responsive dual-mode detection of miRNA-141, a breast cancer biomarker. This method detects miRNA-141 using both electrochemical and colorimetric modes by measuring the output electrical signal of an enzyme-based biofuel cell and the RGB blue value of the electrolyte solution. Tetrahedral DNA and DNA nanorods also are immobilized on the electrode as a biocathode and methylene blue is used as the electron acceptor, which is fixed in the DNA phosphate backbone through electrostatic adsorption. The bioanode catalyzes the oxidation of glucose to produce electrons, which reduces methylene blue to its reduced form, resulting in a high open-circuit voltage (EOCV) and a highger RGB Blue value, enabling dual-mode detection. A reliable linear correlation is observed between EOCV values and miRNA-141 concentrations ranging from 0.0001 to 100 pM, with a detection limit of 21.9 aM (S/N = 3). Additionally, the colorimetric mode also demonstrates a reliable linear correlation with a concentration range of 0.0001-10000 pM, and this method can detect a concentration of 22.2 aM (S/N = 3). This innovative research realizes sensitive and accurate determination of miRNA-141 and provides an important new method for cancer diagnosis.

MnO2 nanoflowers based colorimetric and fluorescent dual-mode aptasensor for sensitive detection of aflatoxin B1 in milk

Aflatoxin B1 (AFB1) with tremendous toxic effects has caused a serious threat to food security. Accurate quantification of AFB1 in food can effectively prevent the risk of human intake of AFB1. Herein, a colorimetric and fluorescent dual-mode aptasensor for accurate and sensitive detection of AFB1 has been developed based on MnO2 nanoflowers (MnO2NFs) for the first time. MnO2NFs could catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxidation product (TMBox) by H2O2, which would be used for visible detection of AFB1. Simultaneously, MnO2NFs can be served as a signal amplifier and reduced by ascorbic acid to generate lots of Mn2+ which would quench the fluorescence of calcein for fluorescent detection of AFB1. Both colorimetric and fluorescent methods have been successfully applied for determination of AFB1 in milk samples with satisfactory results. The proposed dual-mode detection method with high detection sensitivity and accuracy showed great promise for monitoring AFB1 in food.

Polarity Conversion of the Ag2S/AgInS2 Heterojunction by Radical-Induced Positive Feedback Polydopamine Adhesion for Signal-Switchable Photoelectrochemical Biosensing

Efficient tuning of the polarity of photoactive nanomaterials is of great importance in improving the performance of photoelectrochemical (PEC) sensing platforms. Herein, polarity of the Ag2S/AgInS2 heterojunction is converted by radical-induced positive feedback polydopamine (PDA) adhesion, which is further employed to develop a signal-switchable PEC biosensor. In the nanocomposites, Ag2S and AgInS2 achieve electron-hole separation, exhibiting a strong anodic PEC response. Under the irradiation of light, the Ag2S/AgInS2 heterojunction is able to produce superoxide radical and hydroxyl radical intermediate species, leading to the polymerization of dopamine (DA) and the subsequent adhesion of PDA onto the Ag2S/AgInS2 heterojunction (Ag2S/AgInS2@PDA). By constructing a new electron-transfer pathway with PDA, the polarity of the Ag2S/AgInS2 heterojunction is converted, and the PEC response changes from anodic to cathodic photocurrents. In addition, since the photoreduction activity of PDA is stronger than that of the Ag2S/AgInS2 heterojunction, more superoxide radical can be produced by Ag2S/AgInS2@PDA once PDA is generated, thereby promoting the generation of PDA. Consequently, a positive feedback mechanism is established to enhance the polarity conversion of the Ag2S/AgInS2 heterojunction and amplify the responding to DA. As a result, the bioanalytical method is capable of sensitively quantifying DA in 10 orders of magnitude with an ultralow limit of detection. Moreover, the applicability of this biosensor in real samples is identified by measuring DA in fetal bovine serum and compared with a commercial ELISA method. Overall, this work offers an alternative perspective for adjusting photogenerated carriers of nanomaterials and designing high-performance PEC biosensors.

Ultrasensitive Photocathodic Biosensor Based on the Cu2O/PTB7-Th/PDA+ Composite with Enhanced Photoelectrochemical Performance for the Detection of MicroRNA-375-3p

Herein, an ultrasensitive photocathodic biosensor was fabricated based on Cu2O/PTB7-Th/PDA+ photoactive materials with high photocarrier separation efficiency for the detection of microRNA-375-3p. Impressively, the photocathodic signal of the Cu2O material was significantly enhanced by using PTB7-Th as an energy level-matching photoactive material to enhance the bulk charge separation and N,N-bis (2-(trimethylammoniumiodide) propylene) perylene-3,4,9,10-tetracarboxydiimide (PDA+) as an interfacial charge transfer mediator to efficiently suppress charge recombination at the photoelectrode/electrolyte interface. Compared with the pristine Cu2O as a photocathode, the obtained Cu2O/PTB7-Th/PDA+ exhibited a 17 times higher photocathodic signal. As a proof of concept, a PEC biosensor was fabricated by using Cu2O/PTB7-Th/PDA+ as a photoactive material and a target-triggered 3D DNA walker integrated with the dumbbell hybridization chain reaction (DHCR) as a signal amplifier to achieve the sensitive detection of microRNA-375-3p with a detection limit of 0.3 fM. This work provided a method to increase the photocurrent signal and the sensitivity of PEC-sensing platforms for the detection of biomarkers and disease diagnosis.

Dual-channel molecularly imprinted sensor based on dual-potential electrochemiluminescence of Zn-MOFs for double detection of trace chloramphenicol

Functionalized metal organometallic frameworks (MOFs) offer unique advantages in the field of sensing due to their versatility and tunable optical properties. In this work, a new dual-potential electrochemiluminescence (ECL) molecularly imprinted sensor using single Zn-MOF signal probe was designed for double detection of trace chloramphenicol (CAP). As dual-signal ECL emitters, Zn-MOFs were firstly modified on the electrode, showing excellent ECL emission in both cathodic and anodic potential. Then the molecularly imprinted polymer (MIP) was electrochemically prepared using o-phenylenediamine (O-PD) and CAP as a template molecule on the Zn-MOFs/electrode. After CAP as a molecular recognition element was eluted and removed from the Zn-MOFs/MIP/electrode, a new ECL sensor was developed for CAP detection by re-adsorption of CAP on the MIP, resulting in "off" of ECL signal. Compared with the conventional single-signal luminophores, Zn-MOFs show more stable and excellent dual ECL signals, which greatly improve the discriminability and accuracy of CAP trace detection. Under the optimal conditions, the linear range of CAP detection was 1 × 10^-14-1 × 10^-8 M, and the minimum limits of detection (LOD) were 2.1 fM and 2.5 fM for cathode and anode ECL, respectively. This is the first time that Zn-MOFs are used as dual-ECL emitters for molecular sensing systems, and the proposed dual-channel sensing system is flexibly applicable to sensitive detection of other antibiotics, which has broad practical application in food safety.

Photoelectrochemical immunoassay of squamous cell carcinoma antigen based on CuO/nitrogen-doped porous carbon-ZnO biolabeling and a type-II In2O3/AgBiS2 heterojunction

AgBiS₂ was hydrothermally synthesized, In₂O₃ was synthesized by hydrothermal method and calcination, and the type-II In₂O₃/AgBiS₂ heterojunction material of an optimized composition ratio was cast-coated on a fluorine-doped tin oxide (FTO) slice to fabricate an In₂O₃/AgBiS₂/FTO photoanode. The signal-attenuated photoelectrochemistry sandwich immunoassay of squamous cell carcinoma antigen (SCCA) was realized on this photoanode, on the basis of a bovine serum albumin/secondary antibody/CuO nanoparticles/nitrogen-doped porous carbon-ZnO bionanocomposite that can competitively absorb light and deplete the electron donor ascorbic acid as well as show the steric hindrance and p-n quenching effects. Under the optimized conditions (e.g., at a bias of 0 V vs. SCE), the photocurrent was linear with the common logarithm of SCCA concentration from 2.00 pg mL^-1 to 50.0 ng mL^-1, with a limit of detection (LOD) of 0.62 pg mL^-1 (S/N = 3). The immunoassay of SCCA in human serum samples gave satisfactory recovery (92.0~103%) and relative standard deviation (5.1~7.8%) results.

Multifunctional Photoelectrochemical Biosensor Based on ZnIn2S4/ZnS QDs@Au-Ag-Reversed Photocurrent of Cu-Metal-Organic Framework Coupled with CRISPR/Cas-12a-Shearing for Assay of Dual Targets

False positives and negatives in bioanalytical assays remain a persistent problem. Herein, a multifunctional photoelectrochemical (PEC) biosensor based on ZnIn₂S₄ (ZIS)/ZnS quantum dots (QDs)@Au-Ag-reversed photocurrent of Cu-metal-organic framework (MOF) coupled with CRISPR/Cas-12a-shearing was innovatively developed for assay of dual targets. First, Cu-MOF as a good PEC material shows cathodic photocurrent. Then, numerous ZIS/ZnS QDs were assembled to the Au-Ag nanoparticles (NPs) to prepare a stable and highly amplified signal probe, which can just match the energy level of Cu-MOFs and realized the polarity-reversed photocurrent of Cu-MOF for the first time. As the empty-core nanostructure of Au-Ag NPs has a high specific surface area and low material density, the bimetallic nanocrystal can much increase the reaction rate and improve the redox efficiency. When target CEA-produced cDNA opened the hairpin DNA (HP1 DNA) on the electrode, the ZIS/ZnS QDs@Au-Ag signal probe was conjugated to the electrode via DNA hybridization, achieving a significantly reversed PEC current for CEA detection. Moreover, the specific binding of kanamycin/aptamer generated the acDNA (activator), which can activate the trans-cleavage activity of the CRISPR-CAS12a system on ssDNA, so the signal probe was sheared and caused the obvious decrease of PEC signal for kanamycin detection. The newly developed ZIS/ZnS QDs@Au-Ag NPs displayed excellent PEC properties and reversed photocurrent to MOF and were combined with the unique CRISPR-Cas12a system to achieve sensitive detection of dual targets, which can open a new polarity-reversed PEC sensing platform for rapid and accurate analysis of multiple targets and can effectively avoid false positives results in clinical testing.

Near-infrared light-induced photoelectrochemical biosensor based on plasmon-enhanced upconversion nanocomposites for microRNA-155 detection with cascade amplifications

Herein, a novel near-infrared (NIR) light-driven photoelectrochemical (PEC) biosensor based on NaYF₄:Yb³⁺, Er³⁺@Bi₂MoO₆@Bi (NYF@BMO@Bi) nanocomposites was elaborately developed to achieve highly sensitive detection of microRNA-155 (miRNA-155). To realize signal enhancement, the coupled plasmonic bismuth (Bi) nanoparticles were constructed as an energy relay to facilitate the transfer of energy from NaYF₄:Yb³⁺, Er³⁺ to Bi₂MoO₆, ultimately enabling the efficient separation of electron-hole pairs of Bi₂MoO₆ under the irradiation of a 980 nm laser. For constructing biosensing system, the initial signal was firstly amplified after the addition of alkaline phosphatase (ALP) in conjunction with the biofunctionalized NYF@BMO@Bi nanocomposites, which could catalyze the conversion of ascorbic acid 2-phosphate into ascorbic acid, and then consumed the photoacoustic holes created on the surface of Bi₂MoO₆ for the enlarging photocurrent production. Upon addition of target miRNA-155, the cascade signal amplification process was triggered while the ALP-modified DNA sequence was replaced and then followed by the initiation of a simulated biocatalytic precipitation reaction to attenuate the photocurrent response. On account of the NIR-light-driven and cascade amplifications strategy, the as-constructed biosensor was successfully utilized for the accurate determination of miRNA-155 ranging from 1 fM to 0.1 μM with a detection limit of 0.32 fM. We believed that the proposed nanocomposites-based NIR-triggered PEC biosensor could provide a promising platform for effective monitoring other tumor biomarkers in clinical diagnostics.

Colorimetric method transforms into highly sensitive homogeneous voltammetric sensing strategy for mercury ion based on mercury-stimulated Ti3C2Tx MXene nanoribbons@gold nanozyme activity

Nanozymes were emerged as the next generation of enzyme-mimics which exhibit great applications in various fields, but there is rarely report in the electrochemical detection of heavy metal ions. In this work, Ti₃C₂T_x MXene nanoribbons@gold (Ti₃C₂T_x MNR@Au) nanohybrid was prepared firstly via a simple self-reduction process and its nanozyme activity was studied. The results showed the peroxidase-like activity of bare Ti₃C₂T_x MNR@Au is extremely weak, while in the presence of Hg²⁺, the related nanozyme activity is stimulated and improved remarkably, which can easily catalyze oxidation of several colorless substrates (e.g., o-phenylenediamine) to form colored products. Interestingly, the product of o-phenylenediamine exhibits a strong reduction current which is considerably sensitive to the Hg²⁺ concentration. Based on this phenomenon, an innovative and highly sensitive homogeneous voltammetric (HVC) sensing strategy was then proposed to detect Hg²⁺ via transforming the colorimetric method into electrochemistry since it can exhibit several unique advantages (e.g., rapid responsiveness, high sensitivity and quantificational). Compared to the conventional electrochemical sensing methods for Hg²⁺, the designed HVC strategy can avoid the modification processes of electrode coupled with enhanced sensing performances. Therefore, we expect the as-proposed nanozyme-based HVC sensing strategy provides a new development direction for detecting Hg²⁺ and other heavy metals.

Versatile FeMoOv nanozyme bipolar electrode electrochemiluminescence biosensing and imaging platform for detection of H2O2 and PSA

In this work, a unique FeMoOv nanozyme-bipolar electrode (NM-BPE) electrochemiluminescence (ECL) biosensing and imaging platform was proposed for the first time to realize sensitive detection of target hydrogen peroxide (H₂O₂) and prostate specific antigen (PSA). Considering the advantage that the cathode and anode poles of the bipolar electrode (BPE) can be modified respectively, this work was carried out using anode equipped with ECL reagent bipyridine ruthenium (Ru(bpy)₃²⁺), and cathode equipped with the Fe-doped molybdenum oxide/Au nanoparticles (FeMoOv/AuNPs) with excellent peroxidase (POD) and catalase (CAT)-like activity. Because FeMoOv/AuNPs show efficient enzyme catalysis effect and can greatly promote the decomposition of H₂O₂, thus the electron transfer rate in the NM-BPE system would be much accelerated to enhance the ECL signal of Ru(bpy)₃²⁺. Based on this principle, this work not only realized sensitive detection of H₂O₂, but also ingeniously designed an sandwich immunosensor using FeMoOv/AuNPs as recognition probe to mediate the ECL response on the anode, achieving highly sensitive detection of PSA. Furthermore, a unique mobile phone ECL imaging system was developed for assay of PSA at different concentrations, which opened a new portable imaging sensing device for bioassays. This work was the first time to combine nanozymes with bipolar electrodes for ECL analysis and imaging, which not only broadened the applications of nanozymes, but also pioneered the new joint ECL research technique of bipolar electrode and ECL imaging in bioassays, showing great application prospect for multiple detection of proteins, nucleic acids and cancer cells.

PEDOT/FeOOH/BiVO4 Nanohybrids with Excellent Photoelectric Performance Promoted by Photothermal Effects for the Ultrasensitive Detection of MicroRNA-375-3p

Herein, a novel photoactive poly(3,4-ethyl-enedioxythiophene) (PEDOT)/FeOOH/BiVO₄ nanohybrid with excellent photoelectrochemical (PEC) efficiency was assembled for the construction of an ultrasensitive biosensor for microRNA-375-3p (miRNA-375-3p) detection. In comparison with the traditional FeOOH/BiVO₄ photoactive composite, the PEDOT/FeOOH/BiVO₄ nanohybrids exhibited markedly enhanced photocurrent due to the promoted interfacial charge separation by PEDOT, which was used not only as an electron conductor but also as a localized photothermal heater to enhance the photogenerated carrier separation. Based on this PEDOT/FeOOH/BiVO₄ photoelectrode and an enzyme-free signal amplification strategy including a target-induced catalytic hairpin assembly (CHA) and hybridization chain reaction (HCR), a PEC sensing platform for the detection of miRNA-375-3p was established, achieving a wide linear range from 1 fM to 10 pM with a low detection limit of 0.3 fM. Moreover, this work provides a general photocurrent enhancement strategy for the development of high-performing PEC biosensors for sensitive detection of biomarkers and early disease diagnosis.

A General Signal Amplifier of Self-Assembled DNA Micelles for Sensitive Quantification of Biomarkers

Owing to the excellent structural rigidity and programmable reaction sites, DNA nanostructures are more and more widely used, but they are limited by high cost, strict sequence requirements, and time-consuming preparation. Herein, a general signal amplifier based on a micelle-supported entropy-driven circuit (MEDC) was designed and prepared for sensitive quantification of biomarkers. By modifying a hydrophobic cholesterol molecule onto a hydrophilic DNA strand, the amphiphilic DNA strand was first prepared and then self-assembled into DNA micelles (DMs) driven by hydrophobic effects. The as-developed DM showed unique advantages of sequence-independence, easy preparation, and low cost. Subsequently, amplifier units DMF and DMTD were successfully fabricated by connecting fuel strands and three-strand duplexes (TDs) to DMs, respectively. Finally, the MEDC was triggered by microRNA-155 (miR-155), which herein acted as a model analyte, resulting in dynamic self-assembly of poly-DNA micelles (PDMs) and causing the recovery of cyanine 3 (Cy3) fluorescence as the DMTD dissociated. Benefiting from the "diffusion effect", the MEDC herein had a nearly 2.9-fold increase in sensitivity and a nearly 97-fold reduction in detection limit compared to conventional EDC. This amplifier exhibited excellent sensitivity of microRNAs, such as miR-155 detection in a dynamic range from 0.05 to 4 nM with a detection limit of 3.1 pM, and demonstrated outstanding selectivity with the distinguishing ability of a single-base mismatched sequence of microRNAs. Overall, the proposed strategy demonstrated that this sequence-independent DNA nanostructure improved the performance of traditional DNA probes and provided a versatile method for the development of DNA nanotechnology in biosensing.

In2O3/CdIn2S4 heterojunction-based photoelectrochemical immunoassay of carcinoembryonic antigen with enzymatic biocatalytic precipitation for signal amplification

This work reported a split-type photoelectrochemical (PEC) immunoassay for the detection of carcinoembryonic antigen (CEA) based on target-induced biocatalytic precipitation (BCP) by using In₂O₃/CdIn₂S₄ heterojunctions as the photosensitizers. The synthesized In₂O₃/CdIn₂S₄ heterojunctions improved the efficiency of charge separation and shortened the electron convey path to enhance the photocurrent, thus exhibiting high conductivity and low complexation rates of photogenerated electrons and holes. In the presence of CEA, horseradish peroxidase (HRP) catalyzed 4-chloro-1-naphthol (4-CN) to produce benzo-4-chloro-hexadienone (4-CD) through H₂O₂. Then, 4-CD was deposited onto the surface of In₂O₃/CdIn₂S₄ to reduce the photocurrent and realized the signal amplification. The PEC immunoassay revealed an excellent photocurrent toward target CEA within a wide range of 0.01-50 ng mL^-1 at a low limit of detection of 2.8 pg mL^-1 under the optimum conditions. Multiple switching light excitation tests demonstrated the good reliability and stability of the fabricated PEC biosensor. The accuracy was acceptable in comparison with human CEA enzyme-linked immunosorbent assay (ELISA) kit.

Photoelectrochemical biosensing platform based on in situ generated ultrathin covalent organic framework film and AgInS2 QDs for dual target detection of HIV and CEA

In this work, a new photoelectrochemical (PEC) biosensing platform based on an ordered two-dimensional (2D) ultrathin covalent organic framework (COF) film and AgInS₂ quantum dots (QDs) has been developed to enable dual-target detection of HIV and CEA. The porous COF film was firstly in situ generated on ITO, displaying super-stable and intense photocurrent with excellent repeatability. Moreover, an effective PEC quenching probe was specifically designed by loading large number of AgInS₂ QDs on Au nanoparticles (NPs). After target HIV-induced cyclic amplification process to generate abundant DNA S0, the Au NPs-AgInS₂ QDs probe was binded to the COF film through DNA hybridization, enabling PEC signal of the COF film to turn "off" for ultra-sensitive detection of HIV. Furthermore, when CEA as the second target specifically binded to its aptamer, the Au NPs-AgInS₂ QDs quenching probe was released, achieving PEC signal "on" of the T-DA COF film for ultra-sensitive detection of CEA. This work opened a unique 2-D COF film-based PEC biosensing platform with excellent signal for rapid detection of dual targets, which can effectively avoid false positives and negatives and shows promising application for early prevention and detection of cancer diseases.

Photothermal-Reagent-Triggered Visual Thermoresponsive and Quantized Photoelectrochemical Dual-Signal Assay

In vitro biosensing chips are urgently needed for early-stage diagnosis and real-time surveillance of epidemic diseases. Herein, a versatile zone with photothermal effects is implanted in the miniature space of a collapsible lab-on-paper photoelectrochemical biosensor for on-site detection of microRNA-141 in body fluids, which can flexibly interconnect the traditional photocurrent signal with functional temperature response. The visualized thermoresponsive results are enhanced by the exciton energy conversion between Fe₃O₄ nanoparticles (Fe₃O₄ NPs) and formed Prussian blue nanoparticles under near-infrared irradiation, which not only presents heat energy gradient variations but also generates color changes. Significantly, the controlled release of Fe₃O₄ NPs is actuated by a target-triggered enzyme assist strand displacement cycle strategy to efficiently improve the accuracy of target temperature signal prediction, which can concurrently mediate photoelectric signal attenuation via promoting the rapid recombination of photoexcited charge carriers on the CuInS₂/CoIn₂S₄ electrode surface, affording dependable ultrasensitive detection results. Benefitting from the ingenious design of the versatile thermoresponsive-photoelectric sensing platform, the preliminary screening and ultrasensitive quantitative analysis can be simultaneously achieved in a single-drop sample. As a consequence, speedy prediction results and satisfied monitoring data are acquired in the ranges of 0.5 pM to 2 nM and 0.001 pM to 5 nM by measuring the temperature change and photocurrent intensity. By right of these advantages, such research paves a prospective paradigm for the manufacture of a visual, rapid, broad-spectrum, and reliable real-time surveillance platform, which allows it to be a promising candidate for epidemic disease home diagnosis and intelligent diagnosis.

Au nanoclusters-decorated WO3 nanorods for ultrasensitive photoelectrochemical sensing of Hg2+

Ultrasensitive photoelectrochemical sensing of Hg2+ is achieved using Au nanocluster-decorated WO3 nanorods as photoactive materials.