Ethylenediamine-Coupled Lysine-Modified Pencil Graphite Electrode for the Quantification of Indigo Carmine

Food colors have a notable role in this 21st century. The use of food colors in our everyday life has increased alarmingly; consequently, there is a growing desire for the detection of food colors. Ethylenediamine-coupled lysine was synthesized for the detection of indigo carmine (IC). This work focuses on the cost-effective, easily disposable, and biocompatible pencil graphite electrode (PGE) for the modification of ethylenediamine-coupled lysine. The synthesized compound can be modified on the surface of a PGE in several ways, including physical adsorption, covalent bonding, drop casting, and electropolymerization. In the present study, the electropolymerization method was used to modify the PGE. The study employed differential pulse voltammetry (DPV) to assess the influence of several parameters, such as monomer concentration, pH of the electrolyte solution, number of polymer cycles, and potential scan rate, on the electrochemical response of IC at the polymerized electrode surface. The polymerized electrode was characterized using scanning electron microscopy (SEM), Fourier transform infrared (IR) spectroscopy, atomic force microscopy (AFM), Raman spectroscopy, and electrochemical impedance spectroscopy (EIS). All surface characterizations demonstrated substantial alterations from the bare PGE surface, confirming the successful polymerization on the surface of electrode. The proposed sensor is specific for IC, while the other structurally similar food colorants showed no response. The proposed sensor is cost-effective, selective, stable, and versatile for detecting IC. The fabricated sensor demonstrated remarkable analytical performance with a broad linear range of 0.4– $110~\mu $ M, an impressively low limit of detection (LOD) of $0.37~\mu $ M, and a high sensitivity of $73.61~\mu $ A/ $\mu $ M/cm2.