Electrochemical Determination of Carbofuran in Tomatoes by a Concanavalin A (Con A) Polydopamine (PDA)-Reduced Graphene Oxide (RGO)-Gold Nanoparticle (GNP) Glassy Carbon Electrode (GCE) with Immobilized Acetylcholinesterase (AChE)

A new biosensor method was developed to determine residual carbofuran in tomatoes in a rapid and convenient fashion based on immobilizing acetylcholinesterase (AChE) on an electrode modified by concanavalin A (Con A)/polydopamine (PDA)-reduced graphene oxide (RGO)-gold nanoparticle (GNP) nanocomposites. The specific binding between Con A and AChE was investigated by the Ellman method and cyclic voltammetry (CV). The synthesis of nanocomposites was monitored by ultraviolet-visible absorption spectroscopy, scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). The results showed that, due to the specific binding and good electrical conductivity, the biosensor had 2.2 times higher bioactivity, leading to high sensitivity with a low Michaelis constant of 0.10 mM. Parameters that affect the response of the biosensor, such as the pH, enzyme loading, ionic concentration, and inhibition time, were optimized. When used for the detection of carbofuran, this biosensor showed a wide range of applicability from 5 µg/kg to 40 µg/kg with a detection limit of 0.012 µg/kg. In addition, the biosensor demonstrated good recovery values of 101% and 90% for 10 µg/kg and 100 µg/kg of the analyte, good stability, high repeatability, and a rapid detection time of 20 min for carbofuran in tomatoes, which provides significant advantages for future analysis.