DETERMINATION OF URIC ACID IN URINE USING A LOW-COST SENSOR AND HYDROGEL-BASED ELECTROCHEMICAL CELL

Uric acid (UA), found in various bodily fluids such as blood, sweat, urine, and tears, is a compound of significant interest for study using diverse analytical methods and sensors. [1] This work proposes a cost-effective approach for determining uric acid in synthetic urine samples, using a stencil electrode and hydrogel-based (originally used for slow watering of plants) electrochemical cells. The sensors were fabricated using a stencil mold on a pre-polished acetate surface, incorporating a 30:70% (w/w) mixture of graphite as the conductive material and stained-glass varnish as the polymeric binder. Following a 24-hour curing period, the electrodes were further refined by polishing with 2000-grit wet sandpaper. The sensors were characterized using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) with the [Fe(CN)₆]³⁻/⁴⁻ redox probe (2.5 mmol L⁻¹). The charge transfer resistance of 588 Ω and the electroactive area of the working electrode was 3.15 mm². For the analysis, the hydrogel is initially immersed in the solution for 6 hours. The influence of pH on UA oxidation was assessed using a 0.1 mol L⁻¹ BR buffer, with pH ranging from 2.0 to 10.0, identifying pH 6.0 as optimal for the analysis. Differential pulse voltammetry was optimized with a step potential of 4 mV, amplitude of 60 mV, and modulation time of 0.1s. The optimized method demonstrated a linear working range of 2.0 to 10.0 µmol L⁻¹, showing excellent analytical performance (LOD = 0.95 µmol L⁻¹) and high sensitivity. The method also exhibited recovery rates between 94% and 106% for uric acid detection in synthetic urine samples.

Acknowledgements. We would like to acknowledge the universities UFJF, and the funding agencies CAPES, CNPq, and FAPEMIG.

References. [1] TIAN, F. et al., Nanomaterials, v. 13, (2023).