Engineering BiOBr/L-cysteine interface with enriched active sites for enhanced photoelectrochemical detection of trace Zn2.

The development of highly sensitive and selective platforms for trace Zn2+ detection is crucial for environmental monitoring and biomedical diagnostics. Herein, a photoelectrochemical (PEC) sensor was constructed using an L-cysteine (L-Cys)-functionalized BiOBr composite, in which surface-interface engineering was adopted to enrich available recognition sites and modulate the interfacial PEC response. Compared with pristine BiOBr, the incorporation of L-Cys introduces abundant Zn2+ binding functional groups and modifies the local surface environment of BiOBr, thereby enhancing the photocurrent response and enabling the selective recognition of Zn2+. The sensor operates through a signal-off mechanism, in which the coordination of Zn2+ with surface-bound L-Cys forms an interfacial coordination layer that partially hinders mass transport and interfacial charge transfer, resulting in a decrease in photocurrent. Under optimized conditions, the platform exhibits a wide linear response ranging from 0.5 to 40 nmol/L, with a low detection limit of 2.69 nmol/L (S/N = 3). Furthermore, the applicability of the sensor is validated in real-world scenarios, demonstrating excellent recoveries in tap water, lake water, and complex biological matrices such as HepG2 cell lysates (recoveries, 96.3-108.5%). This work provides a robust strategy for engineering bio-semiconductor interfaces for the detection of essential metal ions in complicated samples.