Polarity-switchable photoelectrochemical sensor enabled by in situ polydopamine-regulated Z-scheme charge transfer...

Photoelectrochemical (PEC) sensing has emerged as a powerful analytical technique because of its high sensitivity and low background noise. However, most reported PEC sensors rely exclusively on photocurrent intensity as the analytical output, making them susceptible to environmental fluctuations and nonspecific interference, which compromises detection reliability and selectivity. Developing a polarity-resolved PEC sensing strategy that employs photocurrent polarity rather than signal magnitude as the readout therefore represents an attractive yet largely unexplored approach.

Herein, a photocurrent polarity-switchable PEC sensor was developed for dopamine (DA) detection by integrating BiOI/BiOCl, Cu₂O@CuO, and ZnIn₂S₄ into a cascaded heterostructure with well-matched energy levels. Under dual-wavelength excitation, the synergistic effect of energy-band alignment and Z-scheme-like charge transfer facilitated efficient separation and directional migration of photogenerated charge carriers, producing stable bidirectional photocurrent outputs. During sensing, DA simultaneously served as the target analyte and underwent in situ oxidative polymerization to form a polydopamine (PDA) film on the electrode surface. The PDA layer regulated interfacial charge-transfer kinetics through oxygen adsorption and redistribution of charge-carrier migration pathways, thereby inducing photocurrent polarity reversal and amplifying the photoelectrochemical response. More importantly, DA generated a photocurrent polarity opposite to that produced by common interfering species, enabling polarity-resolved discrimination with markedly improved analytical selectivity. The proposed sensor exhibited a wide linear range from 100nM to 5 mM with a detection limit of 33.3 nM under alternating blue and red light irradiation.

This work establishes an analyte-induced photocurrent polarity-switching strategy by coupling heterojunction engineering with interfacial charge regulation. The introduced polarity-resolved sensing mode provides an additional analytical dimension beyond conventional intensity-dependent PEC sensing, improving signal discrimination and anti-interference capability and offering a promising route for dopamine-specific PEC sensing.