A portable paper-based and smartphone-assisted colorimetric sensor for copper oxychloride

Copper oxychloride (CuOxy) is a copper-containing fungicide and bactericide used to combat fungal diseases in fruits, vegetables, and ornamental crops. The maximum residue limit (MRL) for CuOxy is crop- and region-specific. The MRL for CuOxy is set in a range of 5-30 mg kg^-1 for different sources by the European Food Safety Authority (EFSA). Herein, we report a novel colorimetric sensing platform based on coumarin triazole-functionalized silver nanoparticles (CT-AgNPs) for rapid, selective, and highly sensitive detection of CuOxy. The CT-AgNPs-based sensor exhibits excellent sensitivity, with a limit of detection (LoD) of 0.007 µM, a limit of quantification (LoQ) of 0.023 µM, and a linear detection range (LDR) of 0.1-100 µM. The system is efficiently integrated with AI-assisted smartphone detection and paper-based analytical devices (PADs) for real-time, on-site detection of CuOxy. Under optimized conditions, the sensor demonstrated outstanding selectivity, with no substantial interference from other environmental contaminants. The sensor's real-world applicability was verified through testing on actual samples, including tap and river water, along with different fruits and vegetables. To our knowledge, this is the first report of a CuOxy sensor combining both smartphone integration and paper-based analysis. The approach demonstrated high recovery rates in various environmental samples, validating its capability for quantitative CuOxy monitoring and offering a promising tool for ensuring food safety and environmental health.