Preparation of Silver-Copper Bimetallic/Histidine-Functionalized Graphene Quantum Dot/Graphene Hybrid and Its Application in Electrochemical Determination of Chlorpyrifos, Carbofuran and Carbendazim in Cucumber

In order to improve the dispersion of metal nanoparticles on graphene sheets, the histidine-functionalized graphene quantum dot (His-GQD) was used as a bridge to design and prepare silver-copper bimetallic/His-GQD/graphene hybrid (AgCu/His-GQD/G). His-GQD was fixed to graphene oxide by π-π stacking, then combined with Ag ions and Cu ions to form a complex, and finally thermally reduced under the protection of N₂ to obtain AgCu/His-GQD/G. The synthesized hybrid had an unique three-dimensional structure, and Ag and Cu nanoparticles were uniformly dispersed on the graphene sheets. The electrochemical aptamer sensor was constructed based on the hybrid, and the aptamer was connected to Ag and Cu nanoparticles in the hybrid through Ag-N and Cu-N bonds, to modify to the electrode surface, which was used for the determination of chlorpyrifos, carbofuran and carbendazim. The aptamer sensor showed high sensitivity and selectivity. The linear ranges of standard curves of chlorpyrifos, carbofuran and carbendazim were 1.00×10^-2-1.00×10³pmol·L^-1, 1.00×10^-1-1.00×10⁴pmol·L^-1 and 1.00-1.00×10⁶pmol·L^-1, with detection limits (3S/N) of 3.20×10^-3pmol·L^-1, 2.30×10^-2pmol·L^-1 and 2.90×10^-1pmol·L^-1, respectively. The aptamer sensor was used for the determination of carbofuran, chlorpyrifos and carbendazim in cucumber samples, and only carbendazim was detected, with the detected amounts of 1.21 pmol·L^-1 and 1.25 pmol·L^-1. Test for recovery was carried out according to the standard addition method, giving results in the range of 99.3%-100%.