A self-powered photoelectrochemical sensor with ultra-low background based on ZnIn₂S₄@CdS photoanode and Bi₂WO₆...

Self-powered photoelectrochemical (PEC) sensing features no external power supply, fast response, strong anti-interference and high sensitivity, providing a powerful strategy for ultrasensitive detection of β-site amyloid precursor protein cleaving enzyme 1 (BACE1), a key biomarker for early Alzheimer's disease (AD). In this work, a dual-photoelectrode self-powered PEC biosensor with ultralow background signal was constructed. ZnIn₂S₄ was grown in situ on fluorine-doped tin oxide (FTO) via hydrothermal reaction, and CdS quantum dots were loaded through successive ionic layer adsorption and reaction to fabricate ZnIn₂S₄@CdS/FTO photoanode. The obtained photoanode delivered a photocurrent of 279 μA, which was 2.3 times higher than pure ZnIn₂S₄/FTO, benefiting from superior visible light absorption and charge separation capacity. Bi₂WO₆@polydopamine (Bi₂WO₆@PDA) probes were anchored on peptide substrates in 96-well plates. When BACE1 existed, enzymatic cleavage released Bi₂WO₆@PDA heterojunction probes onto bare FTO photocathode to generate obvious photocurrent. In the absence of BACE1, the photocathode remained equivalent to bare FTO without Bi₂WO₆@PDA probe. Under visible light and zero bias, the sensor realized sensitive BACE1 detection with a linear range of 1 fg mL^-1-500 pg mL^-1 with a limit of detection of 0.30 fg mL^-1. The biosensor possessed favorable selectivity and stability with serum sample recoveries of 96.9%-102.5%, and it could be applied to screen BACE1 inhibitors. This self-powered biosensor with near-zero background shows great application prospect in early AD clinical diagnosis.