Electrospun iridium oxide nanofibers for direct selective electrochemical detection of ascorbic acid

We report the electrochemical activity of IrO_x (0 < x ≤ 2) nanofibers prepared by electrospinning for the oxidations of biological species including L-ascorbic acid (AA), 4-acetamidophenol (AP), dopamine (DA), glucose, β-nicotinamide adenine dinucleotide (NADH), and uric acid (UA). Compared to bare glassy carbon electrode, IrO_x nanofibers show high electroactivity for all the tested species and facilitate AA oxidation most significantly, shifting the oxidation potential to the less positive direction by ∼485 mV in linear sweep voltammetry while the oxidation of glucose is almost negligible at both electrodes. The amperometric response of IrO _x nanofibers at the applied potential of -0.01 V (vs. SCE) is linearly proportional to the AA concentration, exhibiting high sensitivity (194.4 ± 6.8 μA mM^-1 cm^-2, n = 5), fast response time (t_95% = 2.9 ± 1.2 s, n = 5), low detection limit (<0.4 μM), and exclusive selectivity over AP, DA, glucose, NADH, and UA at their physiological levels. In addition, excellent potential resolution of IrO₂ nanofibers, sufficient to differentiate AA, DA, NADH, and UA, is confirmed by differential pulse voltammetry. This results support that IrO _x nanofibers are good potential sensing materials selectively for AA and/or simultaneously for AA, DA, NADH, UA in complex biological samples.