Interfacial Charge Regulation in Hollow CuFe2O4/Bi4O5Br2 Heterostructures for Ultrasensitive Photoelectrochemical Detection of Oxytetracycline

Abstract Antibiotic residues are increasingly being regarded as the emerging pollutants worthy of attention. Here, a hollow CuFe2O4/Bi4O5Br2 heterostructure was engineered as an aptamer-free photoactive interface for the highly sensitive determination of oxytetracycline. The hierarchical architecture combines hollow CuFe2O4 nanospheres with flower-like Bi4O5Br2 microspheres, providing enhanced light utilization, abundant interfacial contact sites, and favorable pathways for charge transport. Spectroscopic and electrochemical characterizations reveal pronounced electronic redistribution after heterojunction formation, together with suppressed photoluminescence, reduced interfacial charge-transfer resistance, prolonged carrier lifetime, and substantially enhanced photocurrent generation. Density functional theory calculations further demonstrate a marked work-function mismatch between CuFe2O4 and Bi4O5Br2, supporting spontaneous interfacial electron redistribution, built-in electric-field formation, and an S-scheme charge-transfer pathway that promotes carrier separation while preserving favorable redox capability. Importantly, the coupled interface exhibits substantially stronger adsorption toward oxytetracycline than either individual component. Adsorption of oxytetracycline blocks surface-active sites, perturbs the interfacial charge environment, and suppresses photogenerated carrier transfer, thereby producing a concentration-dependent photocurrent decrease. Under optimized conditions, the resulting CuFe2O4/Bi4O5Br2/GCE platform exhibits a broad analytical range from 5 pM to 80 μM and a detection limit of 2 pM. The sensor also demonstrates satisfactory selectivity, reproducibility, operational stability, and recoveries of 96−105% in soil, water, fish, pork, and beef samples. This work establishes a general strategy for coupling heterointerface charge regulation with adsorption-gated signal transduction and provides a promising route toward simple, recognition-element-free photoelectrochemical analysis of antibiotic contaminants.