Commercial ink-coated PVC: No longer abrading conventional PVC surfaces for electrode fabrication using pencil drawing

Abstract

Using pencil drawing, a rapid “do-it-yourself” approach is reported to fabricate electrochemical sensors on commercial ink-coated polyvinyl chloride (PVC) substrates. Unlike conventional PVC, the ink-coated substrates have a rougher surface, enabling graphite deposition without a mechanical pretreatment step and simplifying the fabrication method. Three-electrode electrochemical sensors were designed with 2B, 6B, and 8B graphite pencils. Regardless of the pencil type, the fabrication process was conducted with the same number of pencil movements while a commercial multimeter monitored the graphite trails’ electrical resistance. 8B graphite pencils exhibited superior performance due to their softness. Such a feature facilitated the graphite exfoliation and deposition, producing continuous conductive trails and enhancing the sensors' electrochemical responses. Similarly to conventional glassy carbon electrodes, the proposed sensors showed a diffusion-controlled electrochemical behavior for the hexaammineruthenium, requiring only 80 µL of solution for electrochemical measurements. The sensors also exhibited repeatability and reproducibility. Additionally, the sensors’ mechanical stability was demonstrated through bending tests, demonstrating robustness. Under optimized conditions, the analytical performance of the sensors was initially evaluated for analytes with forensic and food interest, such as cocaine-free base (COC) and caffeic acid (CA). As a proof of concept, caffeic acid was successfully quantified in tea samples using square wave voltammetry, achieving a low detection limit of 0.37 μmol L-1. Therefore, this work brings a straightforward alternative to fabricating electrochemical sensors using cheap daily-use materials and showcases the resulting device's utility for antioxidant sensing in tea samples.