Colorimetric Sensor Based on the Oxidase-like Activity of Au@MnOx Nanozyme for High-Sensitivity Detection of Malathion

Organophosphorus pesticide residues severely threaten agricultural products. Thus, it is important to explore sensitive and efficient analytical detection methods for target detection. In this study, a lychee-like gold core-manganese oxide shell structure (Au@MnOx) was synthesized, which displays prominent oxidase (OXD)-like activity. It is able to catalyze 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation to a blue product (oxTMB) without the need for hydrogen peroxide. Malathion can inhibit acid phosphatase (ACP) activity, reduce L-ascorbic acid (AA) production, weaken the color-quenching effect, and restore blue color to the system. Based on this “signal inhibition-recovery” mode, a colorimetric sensor was constructed and applied to quantitatively analyze malathion in food matrices, with a limit of detection (LOD) of 1.51 ng/mL. The average recoveries of malathion in cucumber and cabbage samples were in the ranges of 97.2–104.5% and 99.4–102.5%, respectively, with all relative standard deviations (RSDs) less than 7%. This study provides a sensitive and efficient colorimetric detection strategy for malathion, which has significant application value in the field of food safety.