Carbon Black-Assisted Electrochemical Activation of Sugandh Kokila into a Surface-Confined Phyto-Redox Interface for Gallic Acid Sensing

Abstract Plant-derived phytochemicals are attractive alternatives to synthetic redox mediators, but their direct electrochemical use is often limited by weak electron transfer and poor surface retention. In this work, a commercially obtained Sugandh Kokila material (KK), supplied under the label Cinnamomum cecidodaphne, was used as the plant-derived matrix, was converted into a stable, surface-confined, redox-active electrode interface via carbon black (CB)-assisted electrochemical activation. The bare glassy carbon electrode (GCE) showed no reproducible Faradaic response in KK medium. In contrast, GCE/CB generated a stable KK-derived redox layer after in situ cycling and blank transfer in pH 2 HCl:KCl medium. The optimized GCE/CB@KK@ER electrode exhibited E0′ ≈ 0.612 V vs Ag/AgCl, ΓKK = 2.8 × 10–9 mol cm–2, relative standard deviation (RSD) = 4.1%, α = 0.487, and ks = 0.645 s–1, confirming reproducible surface-confined redox behavior. GC–MS and NMR analyses provided tentative chemical information suggesting that the retained electroactive material comprises a chemically heterogeneous KK-derived phenolic/aromatic fraction. The available data do not permit unequivocal assignment of the electrochemical response to a single molecular constituent; accordingly, the retained material is described here as a KK-derived redox-active fraction rather than as an identified molecular mediator. The GCE/CB@KK@ER platform enabled gallic acid oxidation over 5–50 μM by cyclic voltammetry with a sensitivity of 0.5 μA μM–1 and over 5–60 μM by Amperometry at 0.6 V with a sensitivity of 0.04 μA μM–1. The developed sensor showcased a limit of detection (LOD) and limit of quantification (LOQ) of 1.5 μM and 5.0 μM, respectively, with high stability, reproducibility and selectivity when evaluated against common interferents. The novelty of this work lies in converting a chemically complex, initially nonretainable plant-derived matrix into a stable surface-confined electroactive layer through carbon black-assisted electrochemical reconstruction, rather than employing an isolated phytochemical or a presynthesized redox mediator. This establishes a phytochemical-to-redox-interface strategy in which a crude natural matrix is transformed directly into a functional carbon-supported redox-active interface for electrochemical sensing.