Charge transfer accelerated by internal electric field of MoS2 QDs-BiOI p-n heterojunction for high performance cathodic PEC aptasensing

•High quality MoS2 QDs-BiOI p-n heterojunctioned photocathode is designed for self-power cathodic PEC aptasensing platform.•Intense visible light-harvesting, faster photo-generated carrier separation/transfer and magnified photocurrent are noted.•The origin of high photoelectric conversion efficiency is explored.•Reliable cathodic PEC detection of TNF-α is exemplified with an ultralow detection limit.•Feasibility of simplified sensor fabrication procedures by designing heterojunctioned photoelectrode is highlightened. Integrating the advantages of excellent anti-interference and high stability superior to photoanode, cathodic photoelectrochemical (PEC) bioanalysis is promising and competitive in precise monitoring targets in complex matrices. However, serious consideration of the photocathode is far behind the anodic one. Herein, we report a high quality MoS2 QDs-BiOI p-n heterojunctioned material and exemplify the feasibility of constructing cathodic PEC aptasensing platform. Intense visible light-harvesting, high photoelectric conversion efficiency and magnified photocurrent is observed, which origin is detailed explored by various spectroscopic and electrochemical study. Taking the tumor necrosis factor-alpha (TNF-α) as a model analyte and by coupling the simplest target-induced conformational change mechanism, high selectivity and ultrasensitive self-power cathodic PEC detection is exemplified. Stable and reproducible PEC responses are achieved in a wide linear range of 10 fg/mL to 0.1 ug/mL with an ultralow detection limit (5.2 fg/mL) surpassing most sensors reported so far. Monitoring TNF-α in biological system is realized with desired accuracy and satisfactory recovery.