Fabrication and characterization of nanoparticulate and related iridium oxide-based glucose biosensors
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AbstractThe electrochemical oxidation of glucose utilizing nanoparticulate hydrous Ir oxide (IrOx) films, formed using an approach similar to sol-gel (SG) synthesis, was studied in neutral phosphate buffer solution. The results were compared to glucose detection at IrOx films formed electrochemically on bulk Ir wires and foils. The synthesis of the Ir sol involved an Ir precursor (IrCy and a reducing agent (sodium ethoxide) refluxed in ethanol. The sol was found to be composed of stable metallic nanoparticles of Ir (~ 2 nm in dia.) suspended in the solution phase. Several techniques were used to characterize the products and films formed from the Ir sol. Cyclic Voltammetry (CV) results showed that approximately 46% of the IrCl3 was converted to metallic Ir in the sol phase, while the remaining 54% was present in the precipitate phase. The precipitate phase was composed mainly of Ir02, based on the X-Ray Diffraction, CV and Thermogravimetric analysis results, in both pure ethanol and in a 50:50 ethanohwater solvent, employed to stabilize the enzyme, glucose oxidase (GOx). GOx was immobilized in the IrOx films formed by the electrochemical oxidation of the Ir sol in neutral buffer solutions, and the response of these films to glucose was studied under a range of conditions. It was found that these films respond well to glucose in the presence of oxygen, utilizing the oxidation/reduction signal of H2O2 (non-mediated conditions). As well, these films also showed a very good response to glucose in the absence of oxygen by regenerating the GOx active sites via the Ir(III)/Ir(IV) oxide redox sites. When coated with Nafion®, these films showed a very good selectivity towards glucose, and were unresponsive to interferences like ascorbic acid, uric acid and acetaminophen. The characterization of the Ir-GOx sol-derived films using Transmission Electron Microscopy showed that the Ir/IrOx particles retained their nanometer size (2.2 nm in dia). However, the CV results demonstrated that the IrOx electrochemistry was suppressed at high GOx concentrations in the film. The Michaelis-Menten kinetics (MM) plots for these films were examined, and the kinetic parameters, such as the apparent MM constant (K'm ) and the maximum reaction velocity (imax) were also determined. It was shown that K'm values for the mediated conditions are higher than for the non-mediated, at the same GOx concentrations. Also, a deeper analysis of these kinetic parameters shows that glucose detection at sol-based IrOx films is more sensitive, reproducible and stable vs. glucose biosensors fabricated using bulk Ir.
Bibliography: p. 192-200