Electrochemical sensor modified with heterostructure of graphitic carbon nitride/gold nanoparticles for non-invasive uric acid detection in saliva

A gold nanoparticle/graphitic carbon nitride heterostructure nanocomposite was synthesized via an in-situ chemical reduction of Au³⁺ on the surface of graphitic carbon nitride and was applied for the non-invasive electrochemical detection of uric acid (UA) in human saliva. In this configuration, gold nanoparticles (Au-NPs) acted as highly active electrocatalytic sites, while graphitic carbon nitride (g-C₃N₄) served as a high-surface-area scaffold facilitating uniform nanoparticles dispersion and efficient electron transfer. Morphological and elemental characterization using scanning electron microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDX), BET analysis, and infrared spectroscopy (IR) confirmed the homogeneous distribution of Au-NPs anchored to the g-C₃N₄ sheets. Furthermore, electrochemical characterization was performed through electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Electrochemical measurements demonstrated that Au-NPs@g-C₃N₄/CPE generated significantly higher UA oxidation peak currents compared with bare CPE. Under optimized pH conditions, accumulation potential, and differential pulse parameters the sensor exhibited a well-defined linear calibration range 0.5–10.0 μM (r = 0.9943) with a detection limit of 0.31 μM uric acid. Selectivity tests in artificial saliva showed negligible signal deviations (≤ ±2 %) in the presence of common salivary interferents such as ascorbic acid, creatinine, and glucose. Spike and recovery experiments using actual saliva samples achieved recoveries of 95.56-98.27 % confirming high analytical accuracy in complex biological matrices. Furthermore, the electrode retained over 90 % of its initial response after 60 days of ambient storage indicating excellent stability. The synergistic integration of Au-NPs with g-C₃N₄ significantly enhanced catalytic activity, electron transport, and UA adsorption making the Au-NPs@g-C₃N₄/CPE a cost-effective, sensitive, and reliable platform for point-of-care UA monitoring in saliva for clinical diagnostics and health applications.