Guanosine monophosphate-iron coordination nanozyme as a peroxidase mimetic for colorimetric detection of tetracycline antibiotics in food.

Residues of tetracycline antibiotics (TCs) in food pose a serious threat to human health, creating an urgent need for the development of simple, rapid, and highly sensitive detection methods. Herein, guanosine monophosphate-iron coordination nanozyme (Fe-GMP) were synthesized using the self-assembly of guanosine-5'-monophosphate and iron. Based on the peroxidase-mimicking activity of Fe-GMP nanozyme, a novel colorimetric sensor for the colorimetric detection of TCs was developed. Fe-GMP catalyzes the oxidation of chromogenic substrate 3,3',5,5'-tetramethylbiphenylamine (TMB) in the presence of H2O2, producing a characteristic absorption peak at 652 nm. Interestingly, the introduction of TCs significantly enhances the peroxidase-like catalytic activity of Fe-GMP, causing the solution color to deepen from light to dark blue. Under optimized experimental conditions, the sensor exhibited a linear detection range of 0.2 µmol·L- 1 to 6 µmol·L- 1 for tetracycline, with a limit of detection (LOD) as low as 57.9 nmol·L- 1 (26.7 µg·kg- 1). The sensor has been successfully applied to determine tetracycline antibiotics in real milk and honey samples, with spiked recoveries ranging from 90% to 94%. The developed sensor exhibits a typical "signal-on" response mode, effectively avoiding the false-positive issues caused by nonspecific inhibition in traditional "signal-off" sensors. Furthermore, the sensor is cost-effective, highly efficient, and easy to operate, demonstrating great potential for rapid screening in food safety.