Synergistic PET/IFE-driven fluorescence-phosphorescence dual signal quenching in RTP CDs sensor for sensitive thiram monitoring in food safety.

Thiram, a fungicide used to protect fruits and vegetables from fungal diseases, poses severe health risks due to its residues, so rapid and reliable detection methods are required. Herein, we developed a dual signal sensor based on copper-doped room temperature phosphorescence (RTP) carbon dots (CDs) embedded in a boric acid matrix (Cu-CDs@BA) for detecting thiram in fruits and vegetables. The rigid B₂O₃ matrix, formed through high-temperature oxidation of boric acid, suppresses non-radiative transitions and oxygen quenching in the carbon dots, stabilizing RTP and enabling simultaneous fluorescence and phosphorescence emissions. Copper ions within the Cu-CDs@BA acted as recognition sites by forming a Cu²⁺-thiram complex. The dual signal quenching mechanism involved photoinduced electron transfer (PET) and inner filter effect (IFE), which concurrently quenched fluorescence and phosphorescence. This dual signal output established an intrinsic self-calibration mechanism, significantly enhancing detection sensitivity by compensating for environmental changes. The sensor exhibits exceptional selectivity for thiram, rapid response (< 5 min), and simplified operation by eliminating the need for exogenous Cu²⁺ supplementation. The spiked recovery experiments in real food matrices (banana, carrot) verified the practicality and reliability of the method. This work provided a novel strategy for multi-modal rapid detection of pesticide residues, addressing critical needs in food safety and environmental monitoring.