Fluorescence detection based on molecularly imprinted microspheres and graphene quantum dots/graphite carbon nitride for three tetracyclines determination in dairy products

Tetracyclines (TCs) residues in dairy products pose a potential threat to food safety and public health, necessitating sensitive and selective detection methods. In this study, a fluorescence-based sensing method was constructed by embedding nitrogen and phosphorus co-doped graphene quantum dots (NP-GQDs) into graphite carbon nitride (g-C 3 N 4 ). The composite was subsequently combined with doxycycline-specific molecularly imprinted microspheres (MIM) to obtain MIM@NP-GQDs/g-C 3 N 4 . The composite-based assay exhibited a linear range of 2–50 ng/mL (R 2  > 0.99), with detection limits of 0.8–1.8 ng/mL for three TCs. The method showed excellent reproducibility, allowing up to six reuse cycles, and recovery rates in TC-free dairy samples ranged from 83.5 % to 96.7 % (RSD <5 %). This study demonstrated the application of MIM@NP-GQDs/g-C 3 N 4 for TC detection in dairy products, offering a highly selective and reusable fluorescence-based detection strategy.