Polydopamine and phosphate-induced photocurrent polarity reversal and fluorescence quenching dual mechanism for dopamine detection

Photoelectrochemical (PEC)-based dual-mode sensing and photocurrent polarity switchable PEC are highly promising analytical strategies for increasing sensitivity and accuracy. However, the construction of a sensing platform integrating both mechanisms faces challenges. Herein, a novel PEC-fluorescence (FL) dual-mode triple-signal sensing platform is proposed for dopamine (DA) detection based on the polydopamine (PDA) and phosphate-induced FL quenching and photocurrent polarity reversal dual mechanism. Silver sulfide quantum dots (Ag 2 S QDs), acting as both FL probe and PEC enhancer for the SnO 2 and sulfur-doped BiOCl (SnO 2 /SBOC). In the presence of DA, PDA forms and adheres onto the surface of Ag 2 S QDs in alkaline conditions, effectively quenching the FL of Ag 2 S QDs. The resulting PDA@Ag 2 S droplets on the SnO 2 /SBOC and creates a multi-heterojunction structure that significantly enhances the PEC response. PO 4 3− facilitates the substitution of sulfur and chlorine atoms in the SBOC, creating a shielding effect that impedes electron conduction and induces photocurrent polarity reversal of the sensing platform. The detection of DA is achieved with an ultralow detection limit of 1.2 × 10 −8  M and wide linear detection range of 0.20–225 μM. The designed dual-mode, three-signal sensing strategy greatly improves the sensitivity and reliability, enabling self-calibration of the detection results. PDA and phosphate-induced polarity conversion presents a pioneering perspective for advanced biosensing, highlighting its potential for future applications.