A smartphone-powered photoelectrochemical POCT via Z-scheme Cu2O/Cu3SnS4 for dibutyl phthalate in the environmental and food

Ion exchange reaction-mediated highly sensitive and selective photoelectrochemical assay of Hg(II) based on indirect Z-scheme heterostructure of TiO2 NPs/Au/3D tremella-like ZnIn2S4

An indirect Z-scheme heterostructure of TiO2 nanoparticles (NPs)/Au/3D tremella-like ZnIn2S4 as a photoelectrochemical (PEC) substrate was utilized to construct a highly sensitive and selective PEC sensor for the detection of Hg(II) by combining an ion exchange reaction-mediated signal amplification strategy. After assembling TiO2 NPs, Au NPs, and 3D tremella-like ZnIn2S4 step by step on the indium tin oxide (ITO) electrode, the indirect Z-scheme heterostructure was built, in which ZnIn2S4 works as Hg(II)-recognition probe. Importantly, this heterostructure could effectively restrict the rapid recombination of photoinduced carriers to generate an enhanced initial photocurrent for upgrading the sensitivity. With the introduction of Hg(II), the selective Zn-to-Hg ion exchange reaction was activated, and it could in situ form HgS, leading to the quenching of the PEC signal. The designed PEC device presented good performance for Hg(II) assay, with a broad linear range from 0.0005 to 10,000 nM and a detection limit of 0.32 pM. Thus, this protocol is expected to be utilized for elevating food supervision and environmental assessment via Hg(II) determination.

Long-lasting chemiluminescence-based portable biosensor for POCT of food contaminant azodicarbonamide

Azodicarbonamide (ADA) in flour products is easily converted to semicarbazide which greatly threatens human health. Herein, a long-lasting chemiluminescence (CL)-based biosensor was developed for quantitative point-of-care testing (POCT) of ADA. The threonine (Thr)-functionalized Cu-hemin MOFs (Cu-hemin@Thr) could induce persistent CL of luminol with excellent stability. The CL intensity was related to the competition reaction among ADA and a composite of glutathione-silver ions (GSH-Ag+). In the presence of ADA, GSH is oxidized to glutathione disulfide (GSSG), which breaks the coordination between Ag+ and GSH. The CL of the sensing system is then decreased which is expected to be used for ADA detection. By combining a homemade portable device as a detector and a smartphone as an analyzer, quantitative POCT of ADA was successfully achieved. The limit of detection was 0.562 μM (0.065 ppm), which is much lower than the maximum permissible concentration of ADA (45 ppm) in flour extract. The developed strategy demonstrated quantitative POCT capabilities along with advantages of low cost, excellent selectivity, and repeatability, presenting great potential application in food safety and environment monitoring.

Photothermal-assisted S-scheme heterojunction of Cu3SnS4/Mn0.3Cd0.7S for enhanced photocatalytic hydrogen production

Photocatalytic hydrogen evolution is regarded as an economically viable and environmentally benign strategy. However, the practical application of photocatalytic hydrogen production is constrained by the sluggish reaction kinetics and rapid recombination of photogenerated charge carriers. Herein, a Cu3SnS4/Mn0.3Cd0.7S (CTS/MCS) S-scheme photocatalyst with photothermal effect was synthesized via an ultrasound-assisted self-assembly method and applied for the first time to photocatalytic hydrogen evolution. The hydrogen production rate of CTS/MCS-5 reached 72.5 ± 0.8 mmol/h g-1, representing a 3.44-fold increase relative to Mn0.3Cd0.7S, and the apparent quantum yield of CTS/MCS-5 reached 17.5 % at 450 nm. The photothermal effect induced by Cu3SnS4 can elevate the local surface temperature of the catalyst, providing a portion of the energy required for the reaction, thereby reducing the reaction barrier and further promoting photocatalytic reactions. This research highlights the significance of the S-scheme heterojunction and the photothermal effect as an effective strategy to enhance photocatalytic activity, offering new insights for the development of photocatalytic hydrogen evolution technology.

A "super-off" photoelectrochemical biosensor based on Cu-BTC nanozyme quenching strategy for the detection of dibutyl phthalate plasticizer

Ultrasensitive detection of phthalic acid (PAEs) is an extremely critical mission in environmental monitoring. We designed a "super-off" photoelectrochemical (PEC) biosensor by using MoO3/Bi2MoO6 as photoanode and copper(II) benzene-1,3,5-tricarboxylate (Cu-BTC) nanozyme as highly efficient signal quencher. It was found that the PEC signal of MoO3/Bi2MoO6 photoelectric material is very sensitive to the concentration of co-reactor H2O2. Therefore, a target-triggered endonuclease-assisted recycle was employed to convert the target DBP into amount of output DNA, which can trigger the assembly of DNA nanonet for the immobilization of Cu-BTC nanozyme. Thanks to the peroxidase-like activity of Cu-BTC, a "super off" photocurrent was observed due to the consumption of electron donor H2O2 in the electrolyte. Compared with the traditional quenching strategies such as steric hindrance and light energy competition, this enzymatic reaction on the electrode interfaces is more effective to induce the distinct decrease of photocurrent for analysis. Ultimately, the constructed PEC sensor exhibited a broad linear range from 1 fM to 100 nM and a detection threshold of 0.3 fM. This work highlights the significance of using peroxide-mimic enzyme as a signal amplifier in PEC sensing platform for environmental monitoring.

Construction of dual-signal output sensing platform for different scene of rapid and sensitive ochratoxin A detection in corn

Photoelectrochemical (PEC) is a highly sensitive and fast analytical method that can be used at low concentrations, while photoelectrochromic is a simple and low-cost method primarily utilized for high concentration detection. Therefore, we have developed a dual-signal output sensing platform based on both PEC and photoelectrochromism for rapid and sensitive OTA detection. The sensing platform is divided into signal generation (SG) region and signal output (SO) region, which modified with WO3/BiVO4 photoactive nanocomposites and polyaniline (PANI), respectively. By irradiating the SG region, photogenerated electrons are generated and injected into the SO region through the conductive pathway, resulting in a decrease in surface blue polyaniline and a change to green. The smart device can accurately measure the RGB-Green values, enabling the construction of a photochromic visual sensing platform. After immobilizing the OTA aptamer in the SG region, a linear correlation was observed between the concentration of OTA and the RGB-Green value within the range of 20 ng/L ∼250 μg/L. The detection limit was determined to be 8.33 ng/L (S/N = 3). Furthermore, for a more sensitive OTA detection, a PEC sensing platform was developed utilizing the SG region as a photoanode, exhibiting a linear correlation in the range of 2 pg/L∼300 μg/L with a detection limit of 0.8 pg/L (S/N = 3). The detection of these two modes under the requirement of the international standard for the maximum limit realizes the sensitive OTA detection. The RGB-Green is verified to PEC signal, which improves the detection accuracy. The sensing platform has several advantages and is suitable for various application scenarios.

Target-induced enzymatic cleavage cycle amplification reaction-gated organic photoelectrochemical transistor biosensor for rapid detection of okadaic acid

Okadaic acid (OA), a predominant toxic entity in Diarrhetic Shellfish Poisoning (DSP), carries substantial significance for both marine ecosystems and human well-being. The nascent organic photoelectrochemical transistor (OPECT) biosensor has emerged as a promising biometric methodology, poised to offer a fresh realm for the detection of marine biotoxins. In this work, a biosensor utilizing signal amplification based on Cd0.5Zn0.5S/ZnIn2S4 quantum dots (CZS/ZIS QDs) in OPECT was proposed for OA detection, where ZIS QDs were labeled on aptamer and a substantial quantity of QDs were generated via cyclic shearing facilitated through target-induced Exo I enzyme. Owing to the sensitizing influence of ZIS QDs on CZS, the photoelectric conversion efficiency was augmented, culminating in a notable anodic photocurrent upon exposure to light, thereby inducing a transformation in the channel state of the polymer poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) and consequently producing a remarkable modification in the channel current. The detection limit of the biosensor as low as 12.5 pM and a superior stability and specificity was confirmed, which also showed commendable outcomes in actual samples testing. Consequently, this study not only introduces a novel pathway for swift OA detection, but unveils a novel perspective for future expedited and convenient on-site detection of marine biotoxins.

Comprehensive and Sensitive Analysis of Total PAEs Using a Label-Free Zero-Voltage Photoelectrochemical Biosensor

The sensing of phthalate esters (PAEs) is vital for people's health and environmental protection. This study aimed to develop a highly sensitive and selective photoelectrochemical (PEC) biosensor for PAEs analysis in complex samples. The biosensor is based on a CdS nanoparticle/TiO2 nanotube (CdS NP/TiO2 NT) electrode substrate and a truncated PAEs aptamer (PAEs-apt). By exploiting spatial variations in the potential resistance of the sensing interface, the biosensor achieved superior sensitivity in determining the concentration of PAEs compared to the SELEX aptamer. It exhibited a linear correlation in the range of 0.005 to 1 ng/mL with a detection limit of 1.67 ng/L. Furthermore, the biosensor displayed excellent selectivity for PAEs, with an analysis error factor below 0.277 when the concentration of interfering species was 100 times that of the target. The high performance of the biosensor was attributed to the excellent photoelectronic properties of CdS NPs/TiO2 NTs, high density of PAEs-apt for PAEs, high affinity of PAEs-apt for PAEs, and specific recognition of PAEs. Notably, this PEC biosensor could be used for the PAEs assay in urine and water samples, providing a sensitive and simple analytical method for detecting the same class of compounds with similar chemical structures in complex samples.

Au@Pt nanoparticles-based signal-enhanced lateral flow immunoassay for ultrasensitive naked-eye detection of SARS-CoV-2

With SARS-CoV-2 N protein as a model target, a signal-enhanced LFIA based on Au@Pt nanoparticles (NPs) as labels is proposed. This Au@Pt NPs combined the distinguished localized surface plasma resonance (LSPR) effect of Au NPs and the ultrahigh peroxidase-like catalytic activity of Pt NPs. Au@Pt NPs could trigger substrate chromogenic reaction, generating a color signal orders of magnitude darker than their intrinsic color. In the detection, after the coloration of the strips, 3,3',5,5'-tetramethylbenzidine (TMB) and H2O2 were added, and a dark blue chelate (OxTMB) was produced soon, enhancing the band color significantly. After the signal amplification, the naked-eye detection limit for N protein reached 40 pg/mL. The detection sensitivity enhanced more than 1000 times than that without signal amplification. Compared with mainstream LFIA requiring complex readout instruments, the Au@Pt-based LFIA achieved a comparable sensitivity using naked eyes detection. This point is crucial, especially for unprofessional users or low-resource areas. Hence, this signal-enhanced LFIA may serve as a sensitive, cost-effective, and user-friendly detection method. It can shorten the testing window period and help identify early infections.

A sensitive fluorescence biosensor based on ligation-transcription and CRISPR/Cas13a-assisted cascade amplification strategies to detect the H1N1 virus

We propose a sensitive H1N1 virus fluorescence biosensor based on ligation-transcription and CRISPR/Cas13a-assisted cascade amplification strategies. Products are generated via the hybridization of single-stranded DNA (ssDNA) probes containing T7 promoter and crRNA templates to a target RNA sequence using SplintR ligase. This generates large crRNA quantities in the presence of T7 RNA polymerase. At such crRNA quantities, ternary Cas13a, crRNA, and activator complexes are successfully constructed and activate Cas13a to enhance fluorescence signal outputs. The biosensor sensitively and specifically monitored H1N1 viral RNA levels down to 3.23 pM and showed good linearity when H1N1 RNA concentrations were 100 pM-1 µM. Biosensor specificity was also excellent. Importantly, our biosensor may be used to detect other viral RNAs by altering the sequences of the two probe junctions, with potential applications for the clinical diagnosis of viruses and other biomedical studies.

Recent Progress in Photoelectrochemical Sensing of Pesticides in Food and Environmental Samples: Photoactive Materials and Signaling Mechanisms

Pesticides have become an integral part of modern agricultural practices, but their widespread use poses a significant threat to human health. As such, there is a pressing need to develop effective methods for detecting pesticides in food and environmental samples. Traditional chromatography methods and common rapid detection methods cannot satisfy accuracy, portability, long storage time, and solution stability at the same time. In recent years, photoelectrochemical (PEC) sensing technology has gained attention as a promising approach for detecting various pesticides due to its salient advantages, including high sensitivity, low cost, simple operation, fast response, and easy miniaturization, thus becoming a competitive candidate for real-time and on-site monitoring of pesticide levels. This review provides an overview of the recent advancements in PEC methods for pesticide detection and their applications in ensuring food and environmental safety, with a focus on the categories of photoactive materials, from single semiconductor to semiconductor-semiconductor heterojunction, and signaling mechanisms of PEC sensing platforms, including oxidation of pesticides, steric hindrance, generation/decrease in sacrificial agents, and introduction/release of photoactive materials. Additionally, this review will offer insights into future prospects and confrontations, thereby contributing novel perspectives to this evolving domain.