Ultrasensitive Voltammetric and Impedimetric Aptasensor for Diazinon Pesticide Detection by VS Quantum Dots-graphene Nanoplatelets/carboxylated Multiwalled Carbon Nanotubes As a New Group Nanocomposite for Signal Enrichment

Polluted water and groundwater resources contaminated by pesticides are among the most important environmental distresses. Therefore, a simple, ultrasensitive, and selective electrochemical aptasensor is proposed for diazinon (DZN) determination as an organophosphorus compound. The vanadium disulfide quantum dots (VSQDs) were synthesized by a facile hydrothermal method and doped on the graphene nanoplatelets/carboxylated multiwalled carbon nanotubes (GNP/CMWCNTs) as a new group of nanocomposite. The prepared nanocomposite (VSQDs-GNP/CMWCNTs) on a glassy carbon electrode (GCE) was incubated with the DZN binding aptamer (DZBA) through electrostatic interaction (GCE/VSQDs-GNP/CMWCNTs/DZBA). The modified electrode was used for the low detection of DZN by monitoring the oxidation of [Fe(CN)6] as the redox probe. The characterizations of the modified electrode were performed by several electrochemical methods include: cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Also, the prepared nanocomposite was characterized with field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), UV-Vis absorption spectroscopy, fourier transform infrared (FT-IR), fluorescence emission spectroscopy, dynamic light scattering (DLS), elemental mapping, and energy dispersive spectroscopy (EDS). The DZBA selectively adsorbs DZN on the modified electrode, leading to a decrease and increase in the current of DPV and charge transfer resistance (R) of EIS, respectively, as analytical signals. The developed electrochemical aptasensor at the optimal conditions have low limits of detection (LOD) equal to 1.1 × 10 and 2.0 × 10 mol L with wide dynamic ranges of 5.0 × 10-1.0 × 10 mol L and 1.0 × 10-1.0 × 10 mol L for DPV and EIS calibration curves, respectively. Finally, this aptasensor had good selectivity, stability, reproducibility, and feasibility for the DZN detection in various real samples.