Sensitive Detection of Kynurenic Acid from Biological Fluids Using a Flexible Electrochemical Platform Based on Gold Nanoparticles and Reduced Graphene Oxide

Kynurenic acid (KA), a key metabolite of tryptophan (TRP) via the kynurenine pathway, plays a significant role in various physiological and pathological conditions, including neurodegenerative diseases, depression, and schizophrenia. This study aims to develop a flexible and sensitive electrochemical sensor platform for the direct detection of KA in biological fluids. Custom carbon-based electrodes were fabricated using specialized inks and a flexible plastic substrate, followed by functionalization with a composite film of gold nanoparticles, graphene oxide (GO), and polyethyleneimine (PEI). The GO was electrochemically reduced to enhance conductivity and sensitivity for the target analyte. The sensor platform was characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). An optimized differential pulse voltammetry (DPV) method was employed for KA detection. The developed sensor demonstrated a detection limit of 0.3 nM and was effective across a concentration range of 1 nM to 500 µM. These findings highlight the potential of this electrochemical sensor as a reliable, rapid, and cost-effective tool for KA detection in various biological samples, offering significant advantages over traditional methods in terms of sensitivity and simplicity.