Gold nanoparticles and nitrogen-doped carbon dots based fluorescent nanosensor for ultrasensitive detection of thiram in hawthorn

Development of highly efficient and sensitive methods for trace detection of pesticides in foods is in great need. In this study, a signal “on–off-on” fluorescent nanosensor was proposed based on gold nanoparticles (AuNPs) and biomass derived nitrogen-doped carbon dots (N-CDs) for accurate qualitation and quantitation of thiram in hawthorn. The water-soluble orange peel-derived N-CDs were obtained through a facile one-step microwave-assisted synthesis strategy. The fluorescence of biomass N-CDs could be effectively quenched by AuNPs through inner filter effect (IFE), and recovered when AuNPs were aggregated. In the presence of thiram, N-CDs specially bound with AuNPs through Au-S bonds, causing the aggregation of AuNPs with a visible color change from red to blue, accompanying with the release of N-CDs and a recovery of fluorescence. The restored fluorescence intensity was relevant with the added amount of thiram in a concentration-dependent manner for reliable quantitation. Under the optimized conditions, the newly-developed fluorescent nanosensor exhibited high selectivity for thiram out of other six interfering pesticides, as well as excellent sensitivity with an ultralow detection limit of 4.7 ng/mL and a wide detection range of 10–200 ng/mL. The practical application of the established nanosensor in the spiked hawthorn samples confirmed satisfactory recoveries of 102.22–107.57% with relative standard deviations (RSDs) lower than 5%. The results indicated the feasibility, practicality and wide application prospect of the proposed fluorescent nanosensor for thiram in foods and other commodities.