Ultrasensitive split-type electrochemical sensing platform for sensitive determination of organophosphorus pesticides based on MnO2 nanoflower-electron mediator as a signal transduction system.

Organophosphorus pesticides (OPs) are extensively used worldwide as agrochemicals; however, excess use may threaten the health of humans. Thus, it is an urgent need to develop a sensitive method for determination of OPs. Herein, a simple and sensitive split-type electrochemical method was developed by using MnO2 nanoflower-electron mediator as a signal transduction element. The MnO2 nanoflower-electron mediator was synthesized and shows an excellent electrochemical signal attributed to the high specific surface area of MnO2 nanoflower. Meanwhile, the inhibition of OPs on butyrylcholinesterase (BChE) was carried out in the homogeneous system. In the absence of target molecule, a large number of thiocholines (TCh) were yielded from hydrolysis of acetylthiocholine (ATCh) by BChE. The MnO2 nanoflower was cracked, and subsequently, multiple electron mediator molecules were released from the platform after treated with TCh, thus decreasing the electrochemical response. Furthermore, the inhibition of OPs on BChE resulted in the reduced generation of TCh, thus inducing the recovery of electrochemical signal. Under the optimal experimental, dichlorvos can be detected in a wide range of 10-6-10-10 M, with a detection limit of 3 × 10-10 M. Moreover, the assay was successfully used to analyze dichlorvos in cucumber juice and pear juice, showing a great promising potential for detecting organophosphorus pesticides in complex samples. Graphical abstract In this assay, a split-type electrochemical biosensor was proposed for the ultrasensitive determination of organophosphorus pesticides based on the MnO2 nanoflower-electron mediator as an electrochemical signal component.

Rolling circle amplification promoted magneto-controlled photoelectrochemical biosensor for organophosphorus pesticides based on dissolution of core-shell MnO2 nanoflower@CdS mediated by butyrylcholinesterase.

A photoelectrochemical (PEC) aptasensing platform is devised for sensitive detection of an organophosphorus pesticide based on dissolution of core-shell MnO2 nanoflower@CdS (MnO2 NF@CdS) by thiocholine (TCh). TCH is produced from the butyrylcholinesterase-acetylthiocholine system, accompanied by target-triggered rolling circle amplification (RCA). The core-shell MnO2 NF@CdS with excellent PEC performance was synthesized and employed as a photo-sensing platform. The target was detected on a functionalized magnetic probe with the corresponding aptamer. Upon malathion introduction, the aptamer was detached from the magnetic beads, while capture DNA (cDNA, with primer fragment) remained on the beads. The primer fragment in cDNA can trigger the RCA reaction to form a long single-stranded DNA (ssDNA). Furthermore, a large number of butyrylcholinesterase (BChE) were assembled on the long ssDNA strands through the hybridization with the S2-Au-BChE probe. Thereafter, TCh generated from hydrolysis of ATCh by BChE can reduce MnO2 NF (core) to Mn2+ and release the CdS nanoparticles (shell) from the platform electrode, significantly enhancing the PEC signal. Under optimal conditions, the proposed aptasensor exhibited high sensitivity for malathion with a low detection limit of 0.68 pg mL-1. Meanwhile, it also presents outstanding specificity, reproducibility, and stability. Importantly, the sensing platform provides a new concept for detection of pesticide. Graphical abstract Herein, this work devised a photoelectrochemical (PEC) aptasensing platform for sensitive detection of organophosphorus pesticide based on dissolution of core-shell MnO2 nanoflower@CdS (MnO2 NF@CdS) by the as-produced thiocholine (TCh) from the butyrylcholinesterase-acetylthiocholine system, accompanying with the target-triggered rolling circle amplification (RCA).

Enzymatic oxydate-triggered AgNPs etching: A novel signal-on photoelectrochemical immunosensing platform based on Ag@AgCl nanocubes loaded RGO plasmonic heterostructure.

A well-defined Ag@AgCl nanocubes loaded on the reduced graphene oxide plasmonic heterostructure (Ag@AgCl/RGO) was facilely prepared by sacrificial salt-crystal-template process and ethylene glycol-assisted reduction. The Ag@AgCl/RGO heterostructure shows superior photocurrent response and stability under the visible light irradiation. The enhanced performance mainly attributes to the plasmon resonance effect of AgNPs by improving the absorbance and transfer of photogenerated electrons. Significantly, we observed that the photocurrent could be dramatically decreased with the introduction of H2O2 and experimental results demonstrated the etching effect of H2O2 to AgNPs should be responsible for this phenomenon. Inspired by this phenomenon, employing H2O2 that generated from glucose oxidase catalyzed glucose triggered AgNPs etching as a novel signal mode, an improved photoelectrochemical immunosensing platform was constructed by employing Ag@AgCl/RGO heterostructure as photoactive material. As a proof of concept application, the photoelectrochemical immunosensor employed for ochratoxin A (OTA) detection with competitive-type format and it exhibited excellent analytical performance. Under optimized conditions, the photocurrent increased with the concentration of target OTA in the dynamic range of 0.05 to 300 nM with a limit of detection (LOD) of 0.01 nM (4.0 pg mL-1). The immunosensor also showed high sensitivity, good reproducibility, and satisfactory accuracy. Although the methodology proposed here focused on OTA sensing, it could flexibly extend to monitor other targets by replacing the corresponding bio-recognition elements. Thus, this work provides a new paradigm for designing novel photoelectrochemical biosensing mode based on the plasmonic metal/semiconductor heterostructure.