A photoelectrochemical aptasensor based on chlorine-doped double perovskite Cs₂AgBiBr₆ for highly sensitive detection of sulfadiazine

Lead-free double perovskites like Cs₂AgBiBr₆ are attractive for photoelectrochemical (PEC) biosensing, but their charge separation and interfacial kinetics remain suboptimal. Here, chlorine-doped Cs₂AgBiBr₆ (Cl-Cs₂AgBiBr₆) is designed via a controllable halide-doping strategy. DFT calculations and spectroscopic analyses reveal that Cl doping reconstructs the electronic structure and promotes superoxide radical (·O₂^-) generation. Based on this material, a label-free PEC aptasensor is constructed for sulfadiazine. The sensor shows a linear range of 0.01-1000 ng/mL, a detection limit of 0.67 pg/mL, excellent selectivity, and good stability. In spiked milk samples, recoveries range from 89.57% to 104.03%. This work provides a feasible route to enhance double-perovskite-based PEC biosensors for antibiotic residue analysis in complex matrices.