Green nanozyme, rapid sensing: A DES-synthesized Cu-BTC platform for rapid tetracycline detection in food

Rapid detection of antibiotic residues in food is essential for public health. This study aims to develop a highly sensitive colorimetric sensing platform based on a novel nanozyme. To this end, we used a green, tunable, and safe choline chloride/urea-based deep eutectic solvent (DES) to synthesize a metal organic framework, Cu-BTC (BTC: 1,3,5-benzenetricarboxylate), with many highly dispersed copper active sites. As a result, the prepared Cu-BTC showed strong peroxidase-like activity. In the presence of hydrogen peroxide (H 2 O 2 ), it efficiently catalyzed the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to the blue product TMBox. Importantly, we found that tetracycline (TC) specifically and significantly inhibits this color reaction. The inhibition occurred because TC can directly reduce the blue TMBox, suppressing color development. Based on this effect, we developed a new colorimetric method for sensitive TC analysis. The method had a wide linear range (0.025-25 μM) and a very low detection limit (0.0024 μM). Moreover, it was successfully applied to accurately detect TC in complex food matrices such as milk and honey. Thus, this work not only provides a green route to synthesize high-performance nanozymes, but also establishes a simple, fast, and sensitive colorimetric platform for on-site detection of antibiotic residues in food.