Improved sensitivity and selectivity of uric acid voltammetric sensing with mechanically grinded carbon/graphite electrodes

Determination of uric acid (UA) levels in body fluids is important for diagnostics and prevention of severe metabolic disorders. Electrochemical determination of the UA relies on an oxidation signal measurable at different carbon-based electrodes. Improvement of the UA electrochemical sensing has usually been attained via various modifications of the electrode surfaces. In this paper we show that a strong enhancement of the UA oxidation signal can be reached by a simple mechanical grinding of the surfaces of glassy carbon or edge plane-oriented pyrolytic graphite electrodes with SiC particles of an optimum size 15 μm. In contrast to fine polished electrodes (finally with 1-μm particles), the grinded ones exhibited an excellent separation of oxidation signals of ascorbic acid, dopamine (representing most important natural interferents in UA determination), xanthine and hypoxanthine (precursors of UA in purine catabolism), making it possible to detect these substances in a mixture. Enhancement of UA and dopamine (DA) oxidation signals at the grinded electrodes allowed their easy detection at nanomolar levels in up to 10⁴-fold excesses of ascorbic acid. Due to a strong adsorption at the electrode surface, nanomolar concentrations of UA and DA can be determined by ex situ voltammetry. Similarly strong enhancement of oxidation signals was observed for purine nucleobases, guanine and adenine. The grinded electrodes have been tested in analysis of real clinical samples of human serum or urine. An excellent agreement between electrochemical and routine biochemical determination of UA in the biological samples is demonstrated.