Electrocatalytic Reduction and Determination of Dissolved Oxygen at a Poly(nile blue) Modified Electrode

A novel dissolved oxygen (DO) sensor based on poly(nile blue) modified glassy carbon electrodes is described. The modified electrodes were prepared by electrochemical cyclic sweep between −0.6 and +1.0 V in a nile blue solution. The electrochemical behavior of poly(nile blue) displayed a two-electron and two-proton surface-controlled quasireversible process with a charge transfer coefficient of 0.17 and electron transfer rate constant of 0.37 s−1. The modified electrodes showed an excellent electrocatalytic activity for the reduction of DO at pH 4.8–5.5. The catalytic peak current is linear with DO concentration in the range from 1.3×10−6 to 2.6×10−5 mol/L with a calculated detection limit of 7.8×10−7 mol/L at a signal-to-noise rate of 3 and a correlation coefficient of 0.998. The variation coefficient of electrocatalytic current for 10 determinations at 2.6×10−5 mol/L DO concentration was 2.6 %. The voltammetric response of the modified electrodes to O2 reduction showed a Michaelis-Menten's behavior at higher O2 concentrations. The Km value for the sensor was found to be 0.028 mmol/L. The low Km value demonstrated that poly(nile blue) immobilized at glassy carbon electrodes exhibited a high affinity to dissolved oxygen.