Electron-conducting DNA track-mediated BiOI homojunction pre-enhanced platform for DNA walker-guided photoelectrochemical polarity inversion.

Although polarity-inversion photoelectrochemical (PEC) sensing can effectively suppress false-positive and false-negative responses induced by interferents, achieving high sensitivity remains challenging due to signal prereversal suppression and intrinsic signal quenching at DNA-modified interfaces. Herein, we propose an electron-conducting DNA track-mediated BiOI homojunction pre-enhanced platform, which not only effectively facilitates electron transfer to eliminate the inherent signal quenching effect of conventional DNA interfaces, thereby achieving pronounced pre-enhancement of the initial PEC signal, but also guides the DNA walker to achieve photoelectrochemical polarity inversion, enhancing anti-interference capability and detection sensitivity. A morphology-engineered BiOI homojunction is first constructed to generate a strong and stable baseline cathodic photocurrent by promoting efficient charge separation and interfacial transport through the electron-conducting DNA track. Upon microRNA-125b (miRNA-125b) recognition, a catalytic hairpin assembly (CHA)-amplified DNA walker is activated to migrate along the electron-conducting DNA track, directing the in situ accumulation of polydopamine (PDA) as a signal-reversal mediator and inducing a controllable photocurrent inversion from cathodic to anodic. By coupling electron-conducting DNA track-mediated pre-enhancement with walker-guided polarity inversion, this strategy establishes a high-contrast dual photocurrent window, enabling sensitive and rapid detection of miRNA-125b with a linear range from 1 pM to 1 nM and a detection limit as low as 0.13 pM. This work establishes a generalizable PEC sensing strategy that integrates electron-conducting DNA track engineering with signal-polarity modulation, providing a robust platform for quantitative detection of nucleic acids.