Copper ions modulated growth of TiO2/Bi2S3 heterojunction in-situ: An enhanced photoelectrochemical immunosensor coupled with headspace strategy for chloramphenicol determination.

In this study, CuO functions as a signaling modulator that precisely regulates the formation and concentration of H2S through the release of Cu2+ under acidic conditions. The mechanism involves the reaction between Cu2+ and S2- to form CuS, which consumes part of the S2- introduced via Na2S. This process effectively modulates the in situ deposition of dark brown Bi2S3 on the surface of TiO2/Bi3+ electrodes. Owing to the well-matched band structures of Bi2S3 and TiO2, the resulting heterojunction exhibits excellent photoelectric performance. The photocurrent intensity of the TiO2/Bi2S3 heterojunction shows a concentration-dependent relationship with the level of Cu2+. Based on this principle, we developed a novel photoelectrochemical (PEC) immunosensor integrated with a headspace strategy for the detection of chloramphenicol (CAP), using CuO as an immunomarker. The detection range extended from 1.0 to 5000 pg/mL, and the detection limit was as low as 0.57 pg/mL. This innovative sensor leverages the in situ generation of colored Bi2S3-sensitized TiO2, enabling both qualitative photocurrent-based detection and semi-quantitative visual analysis by the naked eye.