Field-deployable smartphone colorimetric sensor for rapid quantification of dichlorvos in coastal waters using...

Organophosphorus pesticides (OPs) are extensively utilized in agricultural production as highly effective insecticides. However, the improper and illicit use of highly toxic OPs can pose a threat to marine ecosystems and human health. Given the limitations of traditional detection technologies, which are time-consuming, operationally complex, and require professional personnel, there is an urgent need for swift detection technology. For that reason, a smartphone-integrated portable colorimetric sensor based on the MnO₂/rGO heterojunction nanozyme was developed, which converted the colorimetric signals into digital signals by using the color sampling function, simplifying the processes of data analysis and result interpretation. After optimizing the detection conditions, the colorimetric sensor demonstrated a broad detection range extending from 10^-4 to 10 ng·mL^-1 for dichlorvos, with a low detection limit down to 1.37 × 10^-6 ng·mL^-1 and a limit of quantification of 3.89 × 10^-6 ng·mL^-1. This addresses the issues of narrow detection range and insufficient precision in traditional colorimetric sensors. It demonstrates high accuracy in seawater samples with 94.5 to 103% recovery rates and relative standard deviations below 5%. Complete analysis requires only 10 to 15 min. The sensor exhibits excellent selectivity against high-concentration interfering ions such as 1.15 × 10⁷ ng·mL^-1 sodium and non-target pesticides along with robust reproducibility showing 1.78% relative standard deviation and maintaining stability over 30 days. Field validation in Beibu Gulf seawater confirmed reliable detection of dichlorvos at 3.34 × 10^-4 ng·mL^-1 concentrations. In this study, with dichlorvos as the model analyte, the colorimetric sensor enables the on-site detection of dichlorvos in seawater. This not only provides a new method for designing high-efficiency nanozymes and developing organophosphorus pesticide detection systems, but also holds great significance for protecting the marine ecosystem and human health.