A Cost-Effective Electrochemical Sensor Using a Graphite Pencil Electrode for Sensitive Quantification of Phenolic Antioxidants in Human Plasma and Food Samples

Abstract

The pressing challenge in electroanalysis revolves around the creation of a user-friendly analytical sensor that is accessible to individuals lacking specialized expertise. Such sensor should offer minimal cost, while simultaneously ensuring high sensitivity and reproducibility. Herein, graphite pencil electrode (GPE) has emerged as a promising electrochemical sensor for the determination of polyphenolic compounds, including gentisic acid (GEN), gallic acid (GA), caffeic acid (CAF), and sinapic acid (SA). To comprehensively explore the electrochemical oxidation processes of these antioxidants, a range of electrochemical techniques, namely cyclic voltammetry (CV), differential pulse voltammetry (DPV), and chronoamperometry (CA), were deployed. The results of these investigations unveiled a diffusional oxidation wave associated with phenolic hydroxyl groups, involving a two-electron/two-proton loss step, occurring within the potential range of 0.4–0.6 V vs. Ag/AgCl. Crucially, the GPE exhibited the capacity to establish linear calibration curves for GEN, GA, CAF, and SA, encompassing concentrations from nanomolar to sub-micromolar which highlighted by the corresponding limits of detection (LoD), recorded at 0.086, 0.046, 0.112, and 0.115 μM, respectively. The heightened sensitivity and reproducibility demonstrated by the GPE underscore its potential as an efficient tool for the determination of polyphenolic compounds. Beyond its analytical capabilities, the GPE displayed remarkable applicability in facilitating on-site, cost-effective determinations of polyphenolic compounds in both plasma and food samples. This versatility positions the GPE as a valuable asset in addressing the challenges associated with electrochemical analysis, making it an attractive option for a wide range of applications where simplicity, affordability, and reliability are paramount.