Analyte-triggered oxidase-mimetic activity loss of Ag3PO4/UiO-66 enables colorimetric detection of malathion completely free from bioenzymes

Detection of pesticide residues is important because it is related to food and environmental safety. Although lots of sensors have been developed and applied for pesticide analysis, most of them rely on the use of vulnerable bioenzymes, weakening the highlights of these sensors. Here we recommend a bioenzyme-free colorimetric assay of malathion, a typical organophosphorus pesticide, based on the analyte inducing the oxidase-mimicking activity loss of Ag3PO4/UiO-66. Compared to counterparts, the Ag3PO4/UiO-66 composite can provide enhanced oxidase-mimetic catalytic activity to trigger the 3,3′-tetramethylbenzidine chromogenic reaction with the participation of dissolved O2. When malathion exists, it rapidly adsorbs onto the composite surface via their unique interactions and significantly shields the oxidase-like activity of Ag3PO4/UiO-66, thus affecting the catalytic chromogenic reaction. With such a principle, sensing of malathion in a wide linear range (0.0083–5.333 μg/mL) was realized with a detection limit 7.5 ng/mL. Given no biological elements were involved in the proposed assay, it exhibited robust and reliable performance in determining malathion in practical samples. Furthermore, a chromogenic hydrogel-based smartphone sensing system was developed for instrument-free on-site analysis of malathion. With good analytical performance and facile operation, our assay and device will find promising applications in phosphothionate pesticide determination.