Biogenic synthesis of a nanocomposite based on gold nanoparticles and exfoliated graphite nanoplatelets as an electrocatalyst for methyldopa detection

In this study, we report the development of an electrochemical sensor modified with exfoliated graphite nanoplatelets (xGnP) and gold nanoparticles (AuNP) synthesized using green grape plant extract (Vitis vinifera L.). The modified electrode, denoted as xGnP/AuNP-Grape/GCE, was successfully applied for the determination of methyldopa (MD) using square wave voltammetry (SWV). The characterization of the AuNP-Grape was performed using UV–Vis and ATR-FTIR spectroscopies, while transmission electron microscopy and X-ray diffraction were employed to analyze the xGnP-AuNP-Grape nanocomposite. The electrochemical properties of the modified electrodes were investigated using electrochemical impedance spectroscopy and cyclic voltammetry. AuNP-Grape/GCE and xGnP-AuNP-Grape/GCE exhibited a remarkable electrocatalytic effect of 250 mV towards MD compared to the bare glassy carbon electrode (GCE). In addition, notably, the utilization of xGnP-AuNP-Grape/GCE as the working electrode induced a change in the electrochemical behavior of MD from irreversible to reversible when compared to GCE. SWV was optimized with appropriate parameters, and a calibration plot for methyldopa was constructed within the concentration range of 0.082–14 µmol L^‒1. The obtained limits of detection and quantification were 0.024 and 0.082 µmol L^‒1, respectively. The proposed xGnP/AuNP-Grape/GCE electrochemical platform demonstrated excellent stability and sensitivity, offering a simple and rapid method for the quantification of methyldopa. The findings of this study contribute to the development of efficient electrochemical sensors for pharmaceutical and clinical analysis and demonstrate the versatility of using plant extract-mediated synthesis of AuNP in sensor applications.