Dual-mode colorimetric and photothermal detection of thiram using a smartphone-integrated platform with an Fe-doped ZIF-8-derived nanozyme.

Abstract

The extensive use of the fungicide thiram in agriculture poses health risks, necessitating sensitive on-site monitoring. Conventional detection methods often rely on costly and unstable biological recognition elements, while many nanozyme-based strategies still depend on complex cascade reactions involving natural enzymes. Herein, we report a robust, enzyme-free dual-mode sensing platform based on Fe-doped ZIF-8 derived nanozyme (Zn-NC/Fe). Through systematic optimization of iron doping, the optimized Zn-NC/Fe5% nanozyme exhibits superior peroxidase-like activity with low Michaelis constants, attributed to abundant Fe-Nx active sites. Thiram specifically passivates these sites via Fe-S coordination, enabling direct inhibition-based detection. Using TMB as substrate, we constructed a colorimetric sensor and a complementary photothermal sensor based on oxTMB's near-infrared light-to-heat conversion. To enable field use, the nanozyme was encapsulated in sodium alginate hydrogel microspheres and integrated with smartphone-assisted RGB readout, achieving an LOD of 11.25 μM and linear range from 20 to 1000 μM. The platform was successfully validated in environmental water and fruit juice samples with recoveries of 95.6-108.2%. Elliptic Joint Confidence Region analysis further confirmed the statistical accuracy of the three modes. This work provides a stable, cost-effective, and user-friendly toolkit for thiram monitoring, advancing food safety applications.