Detection of guanine at a redox polymer modified indium tin oxide electrode

The electrochemical behavior of guanine at a redox polymer film modified indium tin oxide electrode is examined by voltammetry and amperometry. The results indicate that the modified electrode reduces the overpotential of guanine oxidation by as much as 550 mV. The oxidation of guanine is pH dependent and occurs at 0.61 V (versus Ag/AgCl) under physiological conditions, the lowest oxidation potential of guanine ever reported. Rotating disk electrode (RDE) experiments reveal that the kinetics of the electrocatalysis is very fast, and hence the oxidation current is solely controlled by mass-transport process in solution. Guanine is detected amperometrically at 0.65 V at the modified electrode with a sensitivity enhancement of two orders of magnitude over an unmodified electrode. A calibration curve is linear over the concentration range of 8.0 nM–100 μM with a correlation coefficient of 0.997 and a detection limit of 5.0 nM. The modified electrode also shows good anti-fouling properties towards the oxidation product of guanine and surfactants.