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.