Catalytic preference-enabled exclusive bimodal detection of methyl-paraoxon in complex food matrices using double site-synergized organophosphorus hydrolase-mimetic fluorescent nanozymes.

Pesticide sensing crucially safeguards food safety and public health against environmental and health hazards. While oxidoreductase-type nanozymes (peroxidase and oxidase) have been widely used in optical pesticide detection, their susceptibility to redox interference as well as poor target specificity limits practical applications. To overcome the deficiencies, here we developed Ca2+-chelated 2-aminoterephthalic acid on nanosized ceria (Ca-ATPA@CeO2) as an organophosphorus hydrolase mimic. This design integrates stable fluorescence and dual-site catalytic activity to specifically detect methyl-paraoxon (MP) in complex food matrices. The synergy between Ca2+ (hard Lewis acid) and CeO2 creates dual active sites to catalyze MP hydrolysis into yellow p-nitrophenol (pNP), and the latter quenches nanozyme fluorescence via inner filter effect. The system enables cross-validated quantification of MP in complex samples, eliminating redox interference through target-specific catalysis. The bimodal "on" colorimetric (pNP color signal) and "off" fluorescence (nanozyme fluorescence intensity) detection achieved linear ranges within 1-200 μM, providing detection limits of 1.43 μM and 0.087 μM, respectively. Our work proposes a reliable strategy for selective MP detection that can avoid redox interference, also providing a simple yet efficient design of high-activity fluorescent hydrolase mimics with broadened applications in food safety analysis and beyond.