Selective Label-Free Detection of Imidacloprid by a Graphene Quantum Dot Fluorescent Probe

We developed a fluorescence aptamer sensing method based on gold nanoparticles and graphene quantum dots for the rapid detection of imidacloprid residues in Chinese herbal medicines. In the absence of imidacloprid, gold nanoparticles are dispersed in the solution and effectively quench the fluorescence intensity of the quantum dots due to the protective effect of the aptamer. Because of the aptamer's specific recognition of imidacloprid, a complex forms between the two compounds, and the gold nanoparticles are no longer protected by the aptamer and can aggregate. Consequently, the fluorescence intensity of the graphene quantum dots remain unquenched, resulting in fluorescence recovery. Under optimal conditions, the fluorescence intensity showed a good linear relationship with the imidacloprid concentration in the range of 100-3 × 10⁴ ng/mL. The correlation coefficient was 0.9914, and the detection limit was 52.42 ng/mL. The recoveries of imidacloprid in the yam, matrine, and aloe leaf were 92.27-101.7%, and the relative standard deviation was 0.45-4.14%. This method has potential field applications for rapid quantitative analysis of imidacloprid residue.