Formation of MnO₂-coated ITO electrodes with high catalytic activity for enzymatic glucose detection

We present the formation of a cheap and environmentally friendly working electrode material for glucose biosensors with good catalytic properties. The classic electrode in such devices consists of a conductive material modified with the enzyme glucose oxidase. The working principle is the electrochemical detection of hydrogen peroxide as a product of the enzymatic transformation of glucose. As a base material, we offer manganese dioxide; it is a natural highly selective catalyst for the decomposition of H₂O₂ and is electrochemically deposited onto the surface of ITO. We approached the formation of MnO₂ films systematically. By changing parameters such as the deposition method, pH of the electrolyte, and the drying temperature of the precipitate, a series of electrodes were formed. These electrodes were characterized by SEM, electrochemical impedance spectroscopy, and XPS and their electrocatalytic activity was studied. Significant differences in the sensitivity of the electrodes were detected. The manganese dioxide film with the best catalytic characteristics is formed in the electrolyte with pH 1 by cyclic voltammetry and then drying at 60 °C. The surface of the electrode was then modified with a solution of GOx enzyme with a concentration of 2 mg ml^-1 (100-250 units per mg solid). The sensitivity of such an electrode is 117.8 μA mmol^-1 cm^-2. The range of determined concentrations of glucose is from 0.1 mM to 3 mM. The sensitivity is comparable to that of electrodes based on expensive materials such as graphene and noble metals.