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An integrated dual-signal bioassay was devised to fulfil thrombin (TB) ultrasensitive detection by integrating visualization with the photoelectrochemical technique based on G-quadruplex/hemin. During the process, branched sheet embedded copper-based oxides prepared with illumination and alkaline condition play a vital role in obtaining the desirable photocurrent. The switchover of photoelectrochemical signal was realized by the adjustable distance between electron acceptor G-quadruplex/hemin and interface materials due to dissociation of the Cu/Mn double-doped cerium dioxide (CuMn@CeO2)/DNA caused by the addition of TB. Then, CuMn@CeO2 transferred onto visual zones triggered catalytic reactions under the existence of 3,3′,5,5′-tetramethylbenzidine and hydrogen peroxide, making a variation in color recognized by the naked eye and providing visual prediction. Under optimized conditions, this bioassay protocol demonstrated wide linear ranges (0.0001–50 nM), high selectivity, stability, and reproducibility. More importantly, the proposed visual/photoelectrochemical transduction mechanism platform exhibits a lower background signal and more reliable detection results, which also offers an effective way for detecting other proteins and nucleic acids. [ABSTRACT FROM AUTHOR]

The occurrence of Alzheimer's disease (AD) is strongly associated with the progressive aggregation of a 42-amino-acid fragment derived from the amyloid-β precursor protein (Aβ 1-42). Therefore, it is crucial to establish a versatile platform that can effectively detect Aβ 1-42 to aid in the early-stage preclinical diagnosis of AD. Herein, we introduce a specialized split-type analytical platform that enables sensitive and accurate monitoring of Aβ 1-42 based on a self-corrected photoelectrochemical (PEC) sensing system. To realize this design, gelatinized Ti 3 C 2 @Bi 2 WO 6 Schottky heterojunctions were prepared and served as photoelectrodes for tackling the photoinduced charge carriers. Functionalized CaCO 3 @CuO 2 nanocomposites were used as signal converters to detect Aβ 1-42 and amplify the signal further. Benefiting from the glucose oxidation induced acid microenvironment and H 2 O 2 output, the nanocomposites are able to rapidly decompose, producing Ca2+ and Fenton-like catalyst Cu2+. The Cu2+-driven Fenton-like reaction generated ·OH, which accelerated the 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation. Additionally, Ca2+ was cross-linked with alginate inducing gelation on the surface of Ti 3 C 2 @Bi 2 WO 6 Schottky heterojunctions, influencing mass transfer and light absorption. Eventually results in the shift of photocurrent, allowing for precise quantification with a detection limit of 0.06 pg mL−1. The combination of colorimetric variation and the photoelectric effect provide a more accurate and reliable result. This research opens up new possibilities for constructing PEC platforms and beyond. [ABSTRACT FROM AUTHOR]

Abstract The construction of a photoelectrochemical (PEC) strategy for multi-component detection represents a great challenge in the field of sensing. To address these challenges, herein we presented a hollow-channel paper-based PEC analytical platform based on chemiluminescence (CL) addressable strategies excited PEC strategy for multiplexed sensing application. Sandwich-structured CdS quantum dots (QDs)/reduced graphene oxide (RGO)/ZnO nanorods arrays (NRAs) heterostructure where CdS serves as visible light sensitizers, RGO acts as an electron relay between ZnO NRAs and CdS QDs, were simply assembled on the gold nanoparticles modified paper working photoelectrode (Au-PWE). The PEC performance of the CdS/RGO/ZnO can be greatly improved benefiting from the formation of type II band alignment between CdS QDs and ZnO NR as well as the super charge collection and shuttling property of RGO. Multiplexed CL emission could be achieved through controlling the CL co-reagents transport. By the virtue of CL addressable technique and the excellent PEC activity of CdS/RGO/ZnO, a highly sensitive, and selective multiple microRNAs (miRNAs) quantification method was achieved. Such a tailored strategy would break the bottleneck of the current PEC detection techniques in multiplex tracing, as well as serve as a novel concept for designing multi-channel PEC sensing method. Highlights • A high-throughput photoelectrochemical device was constructed on hollow-channel paper based device. • Sandwich-structured CdS quantum dots/reduced graphene oxide /ZnO nanorods heterostructure was prepared. • Functionalized hollow-channel with different capillary forces was created to control the fluids flow rate. • Successive chemiluminescence emission can be realized to excite the photoactive materials based on the flow rate controlling. [ABSTRACT FROM AUTHOR]

The photoelectrochemical (PEC) technique has resulted in substantial progress in chemical sensing applications. However the complicated photoelectrode modification procedures would enable undesired background noise and decreasing sensitivity. Hence, it is important to explore a new approach alternative to inconvenient substrate modification. Herein, inspired by the stimuli-responsive drug delivery systems, an innovative PEC system is developed for efficiently microRNA-21 (miRNA-21) tracing. Hierarchical nanocomposites based on hematite (α-Fe 2 O 3 ) coated self-ordered titanium dioxide nanorod arrays (TiO 2 NRAs) exhibited enhanced response to solar light, promoted charge carrier separation and transfer efficiency was adopted as photoelectrode directly. Functional mesoporous silica nanomaterial (MSN) is prepared as nanocarriers for efficient loading of Cu 2+ , further capped with miRNA-21 responsive capture RNA probe. Thereafter, the capture RNA probe endows the functional MSN with responsiveness to miRNA-21. With the presence of miRNA-21, this system is thus triggered and a quickly release of capped Cu 2+ occurs due to the dissociation of capture RNA probe presented on the MSN surface via base-pair hybridization. The released Cu 2+ was then served as electron acceptor reduced to Cu° at the counter electrode to enhance electron-hole pair separation efficiency, leading to a promoted photocurrent response. Consequently, the miRNA-21 can be accurately quantified. Taking advantage of its sensitivity and specificity, this versatile strategy demonstrates a new route for the design PEC sensing approach without any photoelectrode modification procedure, and holds great potential for biosensing and clinical diagnosis. [ABSTRACT FROM AUTHOR]

A microfluidic paper-based analytical device (μPAD) was simply constructed for highly sensitive detection of L -glutamic acid and L -cysteine. The μPAD featured with two functional zones on one strip of paper achieved by preferable multi-plate ZnO nanoflowers (ZnO NFs) and molecularly imprinting polymer (MIP) membranes. The as-designed μPAD was established based on the inherent relation between the photo-oxidation products and photoelectrochemical (PEC) performance with the highly sensitive detection of biomolecules. The ZnO NFs were utilized to produce photo-oxidation products by driving the reaction between ferrocenemethanol and photogenerated holes under ultraviolet light. The photo-oxidation products easily flowed to MIP membranes along the hydrophilic channel via capillary action. MIP membranes as the receptors specifically recognized the analytes as well as decreased the electron loss by blocking the reduction reaction between electrons and photo-oxidation products. The PEC response was obtained in the processes of electrons transfer and exhibited the direct relationships corresponding to the concentrations of target analytes. The μPAD showed the detection limits toward L -glutamic acid and L -cysteine as low as 9.6 pM and 24 pM, respectively. Moreover, it is interesting to point out that ZnO NFs nanostructure shows superior PEC signal compared with those of ZnO nanospheres, nanosheets, and nanorod arrays. In current work, photo-oxidation products are utilized to achieve highly sensitive PEC detection for biomolecules under ultraviolet light as well as avoid the effects of multiple modifications in the same region on the reproducibility, which is beneficial for opening up rich possibility for designing more efficient analytical strategy. [ABSTRACT FROM AUTHOR]

This work described that one–step synthesis three dimensional anatase hierarchically cactus–like TiO 2 arrays (AHCT) and their application in constructing a novel photoelectrochemical (PEC) and visualized sensing platform based on molecular imprinting technique, which reports its result with the prussian blue (PB) electrode served as the electrochromic indicator for the detection of glycoprotein (RNase B). The AHCT arrays were perpendicularly grown on FTO substrate with tunable sizes, offering many advantages, such as large contact area, rapid charge electron separation and transport. A possible formation process of the interesting AHCT arrays has been investigated based on time–dependent experiment. In addition, the PEC and visualized sensing platform was constructed based on the molecularly imprinted polymer modified AHCT arrays. Specifically, in the proposed system, the more RNase B being, the more insulating layer was formed on the surface of AHCT arrays that impeded the harvesting of light and electron transfer, resulting in the reduction of photocurrent. When upon light illumination, the photogenerated electrons flow through an external circuit to PB, leading to the reduction of PB to prussian white (PW), which is transparent. The rate of decolourization of PB is proportional to the concentration of RNase B. In this way, a visualized PEC sensing platform that gives its quantitative information could be performed by monitoring the change of color intensity. Under optimal conditions, the protocol possessed a detection range of 0.5 pM to 2 μM (r=0.997) and the limit of detection was 0.12 pM toward RNase B. Our method eliminates the need for sophisticated instruments and high detection expenses, making it possible to be a reliable alternative in resource–constrained regions. [ABSTRACT FROM AUTHOR]

In this study, based on in situ generation of CdS quantum dots (QDs) on the surface of branched TiO 2 (B-TiO 2 ) nanorods, an solar innovative photoelectrochemical (PEC) sensing platform was constructed for real-time, and sensitive detection of cellular H 2 S. Specifically, B-TiO 2 nanorods arrays consisting of TiO 2 nanorods directly grown on fluorine-doped tin oxide (FTO) further using TiCl 3 mediated surface treatment of TiO 2 nanorods are designed and fabricated as a new type of photoelectrode. CdS quantum dots (QDs) was formed on the surface of B-TiO 2 nanorods arrays through the reaction between Cd 2+ and S 2- . And a significant enhancement in the photocurrent was obtained that ascribed to the formation of CdS-B-TiO 2 heterostructures, thus leading to sensitive PEC recording of the H 2 S level in buffer and cellular environments. By using Prussian blue (PB) a electrochromic material to capture the photoelectron generated from the photoelectrode, a new visual system was proposed due to the formation of Prussian white (PW), which could be used to visualize the quantum photoelectric effect. This novel PEC sensing platform not only achieved satisfied analysis results toward S 2- , but also showed excellent sensitivity, selectivity, low cost, and portable features. The strategy through the in situ generation of semiconductor nanoparticles on the surface of wide band-gap semiconductor paves the way for the improvements of PEC analytical performance. Meanwhile, the quantitative read-out electrochromic display paves a facile avenue and initiates new opportunities for creation of cheap, miniaturization sensors for other relevant analytes. [ABSTRACT FROM AUTHOR]

A platelike tungsten trioxide (WO 3 ) sensitized with CdS quantum dots (QDs) heterojunction is developed for solar-driven, real-time, and selective photoelectrochemical (PEC) sensing of H 2 O 2 in the living cells. The structure is synthesized by hydrothermally growing platelike WO 3 on fluorine doped tin oxide (FTO) and subsequently sensitized with CdS QDs. The as-prepared WO 3 -CdS QDs heterojunction achieve significant photocurrent enhancement, which is remarkably beneficial for light absorption and charge carrier separation. Based on the enzymatic etching of CdS QDs enables the activation of quenching the charge transfer efficiency, thus leading to sensitive PEC recording of H 2 O 2 level in buffer and cellular environments. The results indicated that the proposed method will pave the way for the development of excellent PEC sensing platform with the quantum dot sensitization. This study could also provide a new train of thought on designing of self-operating photoanode in PEC sensing, promoting the application of semiconductor nanomaterials in photoelectrochemistry. [ABSTRACT FROM AUTHOR]

In this work, a “signal-off” photoelectrochemical DNA sensing strategy was proposed on the basis of the DNA hybridization induced conformational conversion using CdS quantum dots (QDs) sensitized titanium oxide (TiO 2 ) nanorod array as photoactive material. Highly oriented, single-crystalline TiO 2 nanorod arrays were grown directly on fluorine doped tin oxide (FTO) substrate by the hydrothermal method and employed as matrix for immobilization of capturing hairpin DNA probe, whereas CdS QDs as visible light antennae were successively labeled on the terminal of capturing hairpin DNA probe. Compared with pure TiO 2 nanorods array, CdS QDs sensitized TiO 2 nanorods array evidently extended the absorption edge and exhibited enhanced photoelectrochemical response in the visible region. In the absence of the target DNA, the direct attachment of CdS QDs to TiO 2 nanorod array could reduce charge recombination and hence amplify photocurrent intensity. While in the presence of target DNA, the specific recognition of the target DNA with the capturing hairpin DNA–CdS probe would trigger the conformational conversion of capturing hairpin DNA–CdS probe leading to the quenching of photocurrent. Under optimized conditions, this “signal-off” photoelectrochemical sensing strategy shows a linear relationship between photocurrent variation and the logarithm of target DNA concentration in the range from 10 aM to 100 pM with a detection limit of 5.2 aM. Moreover, it exhibits good performance of excellent specificity, high stability, and acceptable fabrication reproducibility. This present strategy opens an alternative avenue for photoelectrochemical signal transduction and expands the applications of photoelectrochemical biosensing and clinical diagnosis. [ABSTRACT FROM AUTHOR]

Abstract: Driven by the urgent demand of high-selectively point-of-care testing device for pesticide, molecular imprinting-photoelectrochemistry (MI-PEC) was introduced into microfluidic paper-based analytical strategy to design a novel paper-based photoelectrochemical (paper-based PEC) protocol. The MI-PEC strategy was constructed based on CdTe quantum dots dotted molecular imprinted polymers (CdTe QDs@MIPs), and triggered by a common ultraviolet lamp (∼365nm, 50$). The paper-based PEC sensor was fabricated by immobilizing CdTe QDs@MIPs on paper-based screen-printed working electrodes (WEs) via gold nanoparticles (Au NPs), which was electrodeposited on the surface of WE to improve the electron transfer efficiency for high sensitivity. Using S-fenvalerate as model analyte, the produced photocurrent from the proposed paper-based MI-PEC sensor upon ultraviolet radiation decreased with the increasing concentrations of S-fenvalerate solution, and the quenched paper-based MI-PEC showed a low detection limit of 3.2×10−9 molL−1. This study has made a successful attempt in the development of highly selective and sensitive photoelectrochemical sensor for S-fenvalerate monitoring. [Copyright &y& Elsevier]

• Exciton-plasmon interactions gated self-checking functional PEC system was developed. • A BiVO 4 -BP p-n heterojunction was explored. • Exciton-plasmon interactions triggered energy transfer between BiVO 4 -BP and Au NPs. • Dual-signal output guarantees accuracy. Current photoelectrochemical (PEC) sensing system usually suffers from false-positive readout caused by the environmental factor. Herein, a PEC sensing platform with wide spectrum responsive based on exciton-plasmon interactions gated energy transfer between photoelectrode and Au NPs was designed for ultrasensitive detection of adenosine by coupling with self-checking function. Specifically, 2D black phosphorus (BP) nanosheets sensitized nanoporous BiVO 4 (BiVO 4 -BP) acted as photoelectrode could harness light from ultraviolet to near infrared and accelerate charge separation, thus obviously promoted PEC performance. The detection mechanism was designed by controlling exciton-plasmon interaction on the influence of energy transfer between photoelectrode and dispersed Au NPs. Taking advantage of the disaggregation of Au NPs aggregates upon the addition of adenosine, which leads to a shift in the plasmonic band of the Au NPs accompanied by a color change of the solution from blue to purplish red enables a naked-eye readout semiquantitation of the adenosine. Meanwhile, the plasmonic shift gates the photocurrent response of photoelectrode for accurate quantitation of the adenosine exposure ranged from 0.1 nM to 1 μM with acceptable reliability. Enabled by the unique mechanism, this approach provides a new horizon for designing multi-functional PEC sensing platform. [ABSTRACT FROM AUTHOR]

Herein, a CRISPR/Cas12a-mediated photoelectrochemical (PEC) biosensor based on entropy-driven catalysis (EDC) cycle amplification technology was presented for identification of miRNA-21. On the one hand, sensitizer methylene blue (MB) was introduced by double-strand DNA (H1-H2) on the electrode modified by ZnIn 2 S 4 nanoflowers and CdS quantum dots (QDs), which further optimized initial photocurrent. On the other hand, compared with traditional work, the two single strands generated by EDC cycle triggered by miRNA-21 were fully utilized, the problem of low utilization of EDC cycle products was cleverly solved and the multiple signal amplification with simpler operation was realized by combining with CRISPR/Cas12a. A signal strand S1 generated by EDC cycle made the MB-labeled single strand (H2-MB) bend into a hairpin structure to approach electrode, maximizing the PEC signal. Another signal strand S2 formed a ternary complex with CRISPR/Cas12a to activate the trans-cleavage characteristics, the MB-labeled hairpin structure was cut randomly, which made MB left electrode to significantly reduce the signal, realizing sensitive identification of miRNA-21. The designed PEC biosensor presented a satisfactory linear relationship within the scope of 10 fM-100 nM, and detection line as low as 1.5 fM, supplying a new idea in biomarkers assay and disease diagnosis. • The ZnIn 2 S 4 /CdS QDs composites nanomaterial provided strong photocurrent signal. • Entropy-driven catalysis cycle products were sufficiently utilized to amplify the signal. • CRISPR/Cas12a system improved the selectivity and sensitivity of the PEC biosensor. [ABSTRACT FROM AUTHOR]