Multicolor nitrogen dots for rapid detection of thiram and chlorpyrifos in fruit and vegetable samples

The development of sensitive fluorescence sensors and efficient preparation of samples is a challenge in the detection of pesticides in complex samples. In this study, multicolor nitrogen dots (M-Ndots) were synthesised via microwave irradiation at 140 °C for 10 min with 5-amino-1H-tetrazole and p-phenylenediamine as precursors, which have a high fluorescence quantum yield of up to 31%. Furthermore, the M-Ndots were employed as fluorescence sensors for pesticide detection by being combined with a gas membrane separation device, to eliminate the interference from the complex sample matrix. In this process, the M-Ndots were used for sensing thiram and chlorpyrifos through their affinities to Cu²⁺ and Fe³⁺, respectively. Because thiram could decompose into volatile CS₂, its derivate was sensed using the fluorescence of M-Ndots via a complexation reaction with Cu²⁺. Chlorpyrifos, due to its volatility, can reduce the Fe³⁺ ion by inhibiting the activity of acetylcholinesterase, which produces H₂O₂ to oxidise Fe²⁺. In a real application, the time consumption for 96 samples was less than 30 min in one run of the gas membrane separation device. The recoveries for thiram and chlorpyrifos ranged from 90.0% to 115.0%, and the analytical results were validated using LC-MS/MS methods, with relative errors ranging from -7.4% to 10.1%.