Cu-triggered ratiometric fluorescence sensor based on dual-emission carbon dots for visual monitoring of thiram in food.

A copper and nitrogen co-doped carbon dots (Cu, N-CDs)-based fluorescent sensor is developed for thiram detection. In detail, with increasing thiram concentration the fluorescence intensity of Cu, N-CDs at 405 nm decreases , while that at 495 nm remains largely unchanged. This phenomenon results from the Cu-induced complex formation, which increases the aggregation of Cu, N-CDs and triggers fluorescence resonance energy transfer. Based on these findings, a good linear correlation is observed ranging from 0 to 100 µM (R2 = 0.99489) thiram under the optimized conditions, with a calculated detection limit (LOD) of 38.7 nM. Moreover, a smartphone-integrated optical sensing platform is developed to enable on-site thiram detection, achieving a LOD of 110.8 nM. Furthermore, this platform has been successfully applied to real samples and shows satisfactory relative recoveries for thiram (96.20%-103.40%) with relative standard deviations ranging from 1.47% to 2.54%. Therefore, this novel Cu, N-CDs based platform provides a helpful strategy for detecting thiram residues in the environment.