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

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 PO₄^3-, 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.