Polarity-Switching Photoelectrochemical Biosensor Enabled by Metal/Semiconductor Nanostructures for Ultrasensitive MicroRNA Detection.

Developing efficient and accurate photoelectrochemical (PEC) sensing strategies to eliminate potential false positive or negative signals is crucial for practical applications. In this work, we report a PEC sensing strategy based on CuO nanoparticle-induced photocurrent polarity switching in a heterostructure of InP/ZnS quantum dots (QDs) combined with PdPt nanospheres (InP/ZnS@PdPt). The PdPt nanospheres not only provide versatile support for loading InP/ZnS QDs but also enable a 10-fold enhancement in the PEC activity of the InP/ZnS@PdPt compared to InP/ZnS QDs, attributed to the combined influence of localized surface plasmon resonance and the Schottky junction. Through a miRNA-155-triggered catalytic hairpin assembly, the introduction of CuO nanoparticles to the InP/ZnS@PdPt photoelectrode surface results in a photocurrent polarity switch from anodic to cathodic. Leveraging the excellent photoelectric conversion efficiency of the InP/ZnS@PdPt heterostructure and the photocurrent polarity switching capability of CuO, the proposed PEC sensing platform demonstrated outstanding assay performance for miRNA-155, with a linear response range from 100 fM to 500 nM, a detection limit of 16.8 fM, and high selectivity and significant potential for practical applications. This study introduces an effective photocurrent polarity switching strategy for PEC biosensing with potential applications in early disease diagnosis and prognosis evaluation.