Colorimetric sensor and visual enzyme sheets for sensitive detection of dimethoate residue in vegetables based on laccase-like activity of coral-like silver citrate

The overutilization of dimethoate may lead to its deposition in both the environment and crops, which potentially induces neurological, respiratory, and hepatic abnormalities upon absorption by organisms. Colorimetry can accurately determine dimethoate, but there are still many challenges in the rapid, convenient, and point-ofcare detection. Herein, based on the inhibitory effect of dimethoate on the laccase activity of silver citrate (AgCit), a smartphone-assisted colorimetric sensor and rapid detection enzyme sheets were constructed. It was demonstrated that dimethoate could adsorb on the surface of AgCit and inhibit the production of semiquinone radicals in the reaction system. Then, the AgCit laccase activity was inhibited, causing the colorimetry sensor and the enzyme sheets turned light red or even colorless. The constructed sensor has higher sensitivity and the limit of detection for dimethoate is 1.0 mu g center dot L-1. Moreover, the developed enzyme sheets have good selectivity and specificity, and display the detection results within 5 min. Thus, the colorimetric sensor and the constructed enzyme sheets are expected to be used for large-scale preliminary detection of dimethoate residues in actual agricultural products.