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 HO and experimental results demonstrated the etching effect of HO to AgNPs should be responsible for this phenomenon. Inspired by this phenomenon, employing HO 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). 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.