Abstract: A method for the determination of methyl parathion (MP), glyphosate (GLY), and acephate (Ace) residues in grains, has been established utilizing three carbon quantum dot-based nano-fluorescent probes based on the fluorescence quenching effect. The carbon quantum dots-based nano-fluorescent probe (CQDs-NFP) captured pesticides through the –COOH and –OH groups on its surface. The nitrosulfur-modified carbon quantum dots-based nano-fluorescent probe (N,S-CQDs-NFP), introducing –NH2 and –SH groups through nitrogen and sulfur doping, thereby enhancing its electron transfer capability, selectively targeted MP and GLY. Furthermore, the L-tyrosine methyl ester modified carbon quantum dots-based nano-fluorescent probe (L-CQDs-NFP) could specifically detect Ace through its enzyme-like catalytic activity. The three types of probes, prepared from corn stalks by the one-step hydrothermal method, exhibited emission peaks at 415, 425 and 455 nm, respectively, when excited at 340 nm. The results indicated that the calibration curve for these three organophosphorus pesticides exhibited a good linear relationship within the concentration range of 0.001 to 16 µg/mL, with determination coefficients ranging from 0.995 6 to 0.998 1. The detection limits (RSN = 3) were found to be between 1.8 and 2.5 µg/kg, and the quantification limits (RSN = 10) ranged from 6.01 to 8.33 µg/kg. Recoveries for spiked samples from 10 types of grains at three concentration levels varied between 95.33% and 105.56%, with relative standard deviations (RSD) below 3.64%. This method was successfully applied to analyze actual samples, demonstrating advantages such as simplicity in operation, rapidity, high sensitivity, low cost of nanomaterials, and excellent performance, thereby making it suitable for detecting organophosphorus pesticide residues in grains.

Key words: carbon quantum dots; fluorescent probes; organophosphorus pesticides; multi-residue