A Cu2+-modulated UCNPs@RBD sensor for sensitive detection of tetracyclines in food based on the spirolactam open-loop reaction

Abuse of tetracycline (TC) leads to the development of drug-resistant bacterial strains that threaten public health. This paper proposed a novel Cu 2+ -modulated UCNPs@RBD sensor for detecting TC. The sensor utilizes rhodamine B derivatives (RBD) that bind to Cu 2+ , forming RBD-Cu through a spirolactam open-loop reaction. The fluorescence of upconversion nanoparticles (UCNPs) is quenched by RBD-Cu via the inner filter effect (IFE). Upon addition of TC, TC-Cu forms due to electron-donor groups in TC, which decreases the generation of RBD-Cu, thereby enhancing the fluorescence of UCNPs . Under optimized conditions, the sensor exhibits remarkable accuracy across a concentration range of 50–50000 µg L −1 , with a limit of detection (LOD) of 1.72 µg L −1 . Moreover, the sensor demonstrates high selectivity for TC, validated by its application in food samples. The relative standard deviation (RSD) in real sample analysis was below 4.17 %, and the results were consistent with the HPLC method ( P > 0.05). Hence, the sensor exhibited a high level of sensitivity and reliability, making it suitable for the detection of TC in food.