Automated air plasma-assisted functionalization of graphite electrodes for enhanced electrochemical sensing of uric acid

A lab-made robotic system is presented that integrates an arc discharge air plasma generator with automated X- and Y-axis motion, enabling rapid treatment (25 s per 0.19 cm²) of graphite sheet (GS) electrodes with improved reproducibility compared to manual handheld plasma treatment. Scanning electron microscopy (SEM) revealed an increase in surface roughness and the formation of 3D nanoflake structures following plasma treatment. Complementary Raman spectroscopy analysis showed an elevated D-to-G band intensity ratio (ID/IG), indicating a higher density of structural defects. Electrochemical characterization using cyclic voltammetry demonstrated enhanced electrochemical responses for ferricyanide and various organic compounds, including catechol, codeine, ketamine, paracetamol, sibutramine, and uric acid. The improvements were observed as increased current intensities and negative shifts in redox peak potentials, reflecting enhanced electron transfer kinetics at the treated electrode surface. The lower charge transfer resistance measured by electron impedance spectroscopy (EIS) and the higher heterogeneous electron transfer rate constant (k0) obtained for plasma-treated GS electrodes are consistent with these results. As proof of concept, treated GS sensors were used to detect uric acid, an important clinical biomarker, in spiked synthetic saliva and urine samples, using optimized differential pulse voltammetry (DPV) conditions. Linear ranges (between 1.0 and 400.0 and 400.0–1000.0 µmol L− 1) and a limit of detection (LOD) of 0.08 µmol L− 1 were achieved. Appropriate recovery values (106–109%) were also obtained for the analysis of spiked samples.