Flower-like Mn7O13/PVP nanozyme with oxidase mimetic activity for selective and colorimetric detection of tetracyclines based on double antigen sandwich immunoassay

Herein, we present a novel magnetic colorimetric immunosensor designed for the ultrasensitive detection of tetracycline. This immunosensor employs Fe₃O₄-TC-mAb conjugates as capture probes and Mn₇O₁₃•5H₂O/PVP-TC-BSA nanozymes as signal probes, operating under a competitive immunoassay format. After magnetic separation of the formed immunocomplexes, the unbound signal probes remaining in the supernatant catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB), yielding a distinct colorimetric signal at 652 nm. This enables the quantitative detection of TC over a broad linear range (50–1000 ng/mL) with an ultra-low detection limit of 0.396 ng/mL. The sensor exhibits excellent accuracy, with recoveries ranging from 95.56 % to 100.79 % in spiked milk samples, and facilitates rapid analysis. Compared to conventional methods, this approach offers significant improvements in both sensitivity and operational efficiency, making it well-suited for food safety monitoring. This research lays a foundation for the development of simple, rapid, and ultrasensitive tetracycline detection technologies, with potential applications extending to food safety and environmental monitoring.