An Inexpensive Biosensor for Uric Acid Determination in Human Serum by Flow-Injection Analysis

Enzyme-modified indium tin oxide microelectrode array-based electrochemical uric acid biosensor

We fabricated a miniaturized electrochemical uric acid biosensor with a 3-aminopropyltriethoxysilane (APTES)-modified indium tin oxide (ITO) microelectrode array (μEA). The ITO-μEA on a glass plate was immobilized with the enzyme uricase, through a cross-linker, bis[sulfosuccinimidyl]suberate (BS³). The enzyme-immobilized electrode (uricase/BS³/APTES/ITO-μEA/glass) was characterized by atomic force microscopy and electrochemical techniques. The cyclic voltammetry and impedance studies show an effective binding of uricase at the μEA surface. The amperometric response of the modified electrode was measured towards uric acid concentration in aqueous solution (pH 7.4), under microfluidic channel made of polydimethylsiloxane. The μEA biosensor shows a linear response over a concentration range of 0.058 to 0.71 mM with a sensitivity of 46.26 μA mM⁻¹ cm⁻². A response time of 40 s reaching a 95% steady-state current value was obtained. The biosensor retains about 85% of enzyme activity for about 6 weeks. The biosensor using μEA instead of a large single band of electrode allows the entire core of the channel to be probed though keeping an improved sensitivity with a small volume of sample and reagents.

Amperometric carbon paste enzyme electrodes for uric acid determination with different mediators

In this study, two new amperometric carbon paste enzyme electrodes for determination of uric acid were developed. The carbon paste was prepared by mixing uricase enzyme, 1,4-benzoquinone or poly(vinylferrocene) (PVF) as a mediator, graphite powder, paraffin oil and then the paste was placed into cavity of a teflon electrode body. Determination of uric acid was performed by oxidation of enzymatically generated H2O2. The effects of enzyme loading, mediator amount, buffer type, pH, buffer concentration, working potential and temperature were investigated for both electrodes. The working range of the 1,4-benzoquinone modified enzyme electrode was 1.9 × 10–8–2.7 × 10–3 M, detection limit 1.9 × 10–8 M and response time 150 s. Optimum buffer type, pH, buffer concentration, working potential, temperature and amounts of enzyme and mediator for 1,4-benzoquinone modified enzyme electrode were found to be Tris, 8.0, 0.20 M, +0.25 V, 30 °C, 2.0 Unit and 13%, respectively. The working range of the PVF modified enzyme electrode was 7.4 × 10–8–7.0 × 10–3 M, detection limit 7.4 × 10–8 M and response time 120 s. Optimum buffer type, pH, buffer concentration, working potential, temperature and amounts of enzyme and mediator for PVF modified enzyme electrode were found to be phosphate, 8.0, 0.05 M, +0.70 and +0.30 V, 40 °C, 2.0 Unit and 10.9%, respectively. The repeatability, storage stability of the enzyme electrodes and interference effects were also investigated. Enzyme electrodes were used for determination of uric acid in serum samples and the results were in a good agreement with those obtained by commercial enzymatic kits.