Multi‐Peak Redox Strategy for Ultrasensitive Adsorptive Stripping Voltammetric Detection of 5‐Hydroxyindole Acetic Acid on a Thermally Oxidized Graphite Felt

The precise determination of 5-hydroxyindole acetic acid (5-HIAA), an essential biomarker for neuroendocrine tumors and neurological diseases, is of paramount importance. Herein, we develop a sensitive electrochemical sensor based on an oxidized graphite felt (OGF) electrode, functionalized with oxygen-containing groups via facile thermal oxidation. The synergistic integration of these moieties with the inherent 3D porous structure facilitates hydrogen-bonding interactions, enabling efficient capture of a crucial oxidative intermediate of 5-HIAA: its cationic free radical. This unique molecular recognition mechanism generates a distinctive six-peak voltammetric signature in cyclic voltammetry, providing deeper insights into the complex oxidation pathway of 5-HIAA. Utilizing adsorptive stripping square wave voltammetry, the OGF sensor achieves a wide linear range of 0.35-26.5 μmol/L and a low limit of detection of 0.094 μmol/L (S/N = 3). The enhanced analytical performance is directly linked to the superior intermediate-trapping capability of OGF, highlighting its potential for reliable biosensing applications.