Smartphone-integrated colorimetric and fluorometric sensor based on copper-doped carbon dots for visual and rapid detection of thiram

Achieving highly selective visual detection of thiram is essential for ensuring food safety and environmental protection. Here, we developed a smartphone-integrated colorimetric and fluorometric dual-mode sensor based on copper-doped carbon dots (Cu-CDs). The Cu-CDs were synthesized via hydrothermal treatment of L-tryptophan and CuCl₂·2H₂O. These Cu-CDs exhibited two fluorescence emission peaks at 350 nm and 450 nm, with a fluorescence quantum yield of 20.8%. Cu²⁺ on the surface of the Cu-CDs could selectively bind to thiram to form a Cu²⁺-thiram complex, which quenched the fluorescence at 450 nm of the Cu-CDs via the inner filter effect and dynamic quenching effect. In contrast, the fluorescence at 350 nm was changed slightly. The color of the solution was changed from colorless to yellow. These changes allowed for a fluorometric and colorimetric dual-mode optical response. The proposed sensor possessed high sensitivity and selectivity and demonstrated reliable performance in real water samples. Its integration with a smartphone further enabled convenient, on-site detection. This work presented a robust and cost-effective strategy for monitoring thiram in applications related to food safety and environmental protection.