Cu2+-Triggered Carbon Dots with Synchronous Response of Dual Emission for Ultrasensitive Ratiometric Fluorescence Determination of Thiophanate-Methyl Residues

Copper ion (Cu2+)-triggered carbon dots (CDs/Cu) with dual emissions were utilized to develop a ratiometric fluorescence sensor for ultrasensitive detection of inert thiophanate-methyl (TM). TM could be recognized by CDs/Cu through π–π stacking and could chelate Cu2+ of CDs/Cu through metal ion coordination, inducing synchronous fluoresent quenching of the dual emission of CDs/Cu based on the excited state intramolecular proton transfer and the ligand-to-metal charge transfer. The fluorescence ratio of CDs/Cu (F416/F481) linearly responded in a TM concentration of 0.10–20.00 μmol/L with an ultralow limit of detection of 2.90 × 10–6 μmol/L. A synchronous response of the ratiometric sensor enhanced the specificity toward TM and presented remarkable capability of anti-interference in complex matrices. The sensor exhibited satifactory accuracy and precision for practical applications with recoveries of 88.33–101.09% and relative standard deviations of 1.61–5.06%, demonstrating an ultrasensitive ratiometric fluorescent nanosensor for detecting pesticides residues in complex matrices.