Stepwise enhanced photoelectrochemical activity of BiOCl by Fe(III)-doping and aptamer immobilization for ultrasensitive detection of tetracycline.

Tetracycline (TC), a widely used broad-spectrum antibiotic in veterinary medicine and agriculture, poses significant environmental and health risks, necessitating rapid and sensitive detection methods. Herein, a novel photoelectrochemical (PEC) aptasensor based on Fe-doped BiOCl (BiOCl@Fe) was developed for TC detection. The synthesized BiOCl@Fe heterostructure exhibited a uniform flake-like morphology, and Fe3+ doping significantly enhanced the PEC response by narrowing the band gap and improving light absorption efficiency. Benefiting from the strong Fe3+-PO43- coordination affinity, the 5'-PO43--terminated aptamer was directly immobilized onto the BiOCl@Fe-modified electrode without exogenous crosslinkers. Notably, this coordination chemistry not only enabled aptamer immobilization but also further enhanced the PEC signal, leading to an ultrasensitive aptasensor for tetracycline with a wide linear range (10 nM-100 μM) and a low detection limit of 1.27 nM. The aptasensor was successfully applied to TC detection in milk samples, demonstrating its potential for food safety and environmental monitoring.