Detection of Biothiols in Vegetables by Switched Fluorescence Sensor with Nitrogen-Doped Carbon Dot

The study established a switchable fluorescent sensor for rapid detection of Hg²⁺ and biothiols. Nitrogen-doped carbon dots(N-CDs)was prepared by citric acid and urea as processors through one-pot hydrothermal method. The surface morphology,ultraviolet/fluorescence spectra and surface group characterization were performed. The detection conditions of biothiols were optimized by using the pH of detection system,Hg²⁺ concentration,and incubation time(fluorescence quenching and recovery time)as single factors and the corresponding standard curve was established under the optimal detection condition. The results showed that the optimal excitation and emission wavelength of N-CDs were 340 and 432 nm respectively,and the fluorescence quantum yield(FLQY)was 32.72%. The optimal detection conditions for glutathione(GSH)were pH=5.0,Hg²⁺ concentration 200 μmol/L,fluorescence quenching of 460 s and fluorescence recovery of 380 s;for cysteine(Cys)were pH=5.6,Hg²⁺ concentration 300 μmol/L,fluorescence quenching of 440 s and fluorescence recovery of 400 s. The sensor had a linear response to 0~300 μmol/L GSH and 100~400 μmol/L Cys,and the detection limit(LOD)was 2.56,3.46 μmol/L respectively under optimal conditions. The recoveries of this method in spiked samples were between 80% and 120%. These results indicated that the sensor showed good selectivity and accuracy for biothiols detection in vegetables,herein providing a new idea for the fast fluorescence detection of biothiols in food matrix.