Detection of Oxytetracycline Residues in Milk Samples Based on the Fluorescence Quenching Effect of AgInS2/ZnS Quantum Dots

Water-soluble ZnS-coated AgInS 2 quantum dots (AIS/ZnS QDs) were synthesized via a one-pot aqueous method, and their crystal structure, surface composition, morphology and optical properties were systematically characterized. Based on the fluorescence quenching effect of AIS/ZnS QDs toward oxytetracycline (OTC), a fluorescence spectrophotometric method was established for OTC detection in milk. Under optimal conditions (QDs preparation at pH 5.5, detection temperature of 20 °C, and detection concentration of 0.160 g/L, with a 25 min reaction time), the relative fluorescence quenching degree (ΔF/F 0 ) showed a good linear correlation with logC (OTC concentration), with a linear equation of ΔF/F 0 = 0.2933 logC + 2.3388 (R 2 = 0.9984), a linear range of 1.22 × 10 -8 to 2.5 × 10 -5 mol/L and a detection limit of 1.82 × 10 -9 mol/L. The spiked recoveries of OTC in milk were 96.9%-107.1%. Furthermore, the possible quenching mechanism was proposed. This work offers insights into AIS-based functional material synthesis and expands their applications in fluorescence analysis.