A low-cost and portable platform for on-site detection of dimethoate using Ag2CO3 nanozymes and smartphone image analysis

Nanozymes have replaced natural enzymes in various biosensing applications. However, they still face certain challenges in terms of heterogeneous recognition, stability, and anti-interference capability, particularly in peroxidase-based biosensing. Herein, we constructed an oxidase-based biosensing platform leveraging the specific interaction of Ag S coordination for the rapid detection of dimethoate. Ag₂CO₃ nanoparticles synthesized via a low-temperature ion-exchange method exhibit oxidase-mimicking activity, enabling them to catalyze the oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to produce a blue oxidation product (oxTMB), which exhibits a characteristic absorption peak at 652 nm. Intriguingly, the presence of dimethoate significantly enhances this oxidase-like activity. The enhancement mechanism is attributed to the specific interaction between dimethoate molecules and the Ag₂CO₃ surface, which increases the exposure of catalytic sites and promotes the generation of reactive oxygen species (·O₂ − and 1 O₂). Based on this phenomenon, a novel colorimetric sensor was developed for dimethoate detection. The color intensity, deepening from light to dark blue with increasing dimethoate concentration (20–200 μg·L −1 ), allows for visual and spectrophotometric quantification with a detection limit of 10.5 μg·L −1 . Furthermore, a portable detection platform was established by integrating smartphone-based image analysis (using RGB values) for on-site quantitation. The method demonstrated high selectivity for dimethoate and was successfully applied to detect dimethoate residues in vegetables with satisfactory recovery rates (84.4%–95.7%). This cost-effective and instrument-free strategy shows great potential for the rapid on-site screening of pesticide residues.