Enzyme-free multicolor sensor for visual detection of malathion based on a bimetallic magnetic nanozyme-mediated gold nanorod etching

Malathion plays an important role in agricultural production, and the accurate detection of malathion residues is essential to ensure food safety. A novel enzyme-free sensing method was proposed by employing bimetallic magnetic nanozymes for both colorimetric quantification and multicolor semi-quantitative detection of malathion. The nanozyme exhibits peroxidase-like activity, catalyzing H 2 O 2 -mediated oxidation of 3,3′,5,5′-Tetramethylbenzidine dihydrochloride (TMB). Malathion inhibits this activity via Zr O P coordination, reducing oxidized TMB (oxTMB) generation. Under acidic conditions, oxTMB is further converted to TMB 2+ , which etches gold nanorods, inducing aspect-ratio variations accompanied by distinct multicolor changes. This method demonstrates low detection limits of 0.68 ng/mL. It does not require biological enzymes and can semi-quantify the malathion concentration through color changes. Thus, it can achieve convenient and accurate quantitative analysis without instruments, meeting on-site detection requirements. This work contributes to food safety and the development of efficient and reliable methods for malathion detection.