Structure-selective colorimetric sensing of dimethoate via suppression of CeO2 nanozyme-triggered Ag NPs formation with smartphone readout.

Selective detection of pesticides, especially the discrimination of structurally similar analogues, is critical for regulating their proper use and ensuring food safety. Dimethoate (DIM), a widely used insecticide, can metabolize in vivo to the more toxic omethoate; however, conventional rapid assays struggled to distinguish between them, leading to residue misestimation and regulatory difficulties. Herein, a CeO2 nanozyme-triggered colorimetric sensor was fabricated for selective detection of DIM. Phosphatase (POP)-mimicking L-Arginine (L-Arg) CeO2 nanoparticles (NPs) hydrolyzed L-ascorbic acid 2-phosphate (AAP) to ascorbic acid (AA) and PO43-, which subsequently reduced Ag+ to Ag NPs, yielding a yellowish-brown color. DIM, however, combined with Ag+ to suppress Ag NPs formation, leading to a color fading. Density functional theory (DFT) calculations revealed that the selective coordination was governed by a bidentate chelation mode involving both the PS and the adjacent CO groups of DIM, which exhibited substantially higher binding affinity than that of omethoate. The sensor exhibited a low detection limit of 5.0 µg L-1 with high anti-interference capability towards other pesticides, including omethoate. The applicability of this sensor was validated by spike-and-recovery experiments in cucumber and cowpea samples. Moreover, a smartphone-based mini-program was developed as a portable detection terminal, enabling real-time image capture, data processing and immediate result readout, thereby facilitating on-site pesticide detection. This work offered a facile and robust route for the selective detection of DIM, and provided a structure-responsive mechanistic paradigm for the rational design of nanozyme-based sensors.