Abstract: Using waste broccoli stems and leaves as the precursor, nitrogen, sulfur and silicon doped carbon quantum dots (CDs) were prepared by hydrothermal carbonization method, and their structural characterization and element analysis were conducted by dynamic light scattering (DLS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Furthermore, according to the principle of enzyme inhibition, a CDs/Fe2+/acetylcholinesterase reaction system was constructed and used to fabricate a fluorescence sensor to detect organophosphorus pesticides. The results showed that the new CDs had a graphene-like structure, with a quantum yield of 9.53% and good water solubility and photoluminescence properties. The particle size was measured to be about 30 nm, nitrogen, sulfur and silicon were found to be present in the surface of CDs, and the dots contained functional groups dominated by oxygen and nitrogen. The limit of detection (LOD) of the fluorescence sensor for dichlorvos was about 8 ng/mL. Finally, the oxidized/reduced CDs/Fe2+ fluorescent probe was applied to the determination of dichlorvos in commercial foods. The results showed that the recoveries for the spiked samples ranged from 90% to 97% with relative standard deviation (RSD) not larger than 1% (n = 3), indicating the practicality and accuracy of the probe. The CDs/Fe2+ fluorescent probe has a broad prospect for the detection of organophosphorus pesticides in the fields of biology and food in the future.

Key words: stems and leaves of broccoli; carbon dots; characterization; dichlorvos; fluorescence detection