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 (muEA). The ITO-muEA 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-muEA/glass) was characterized by atomic force microscopy and electrochemical techniques. The cyclic voltammetry and impedance studies show an effective binding of uricase at the muEA 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 muEA biosensor shows a linear response over a concentration range of 0.058 to 0.71 mM with a sensitivity of 46.26 muA 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 muEA 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.