Scanning electrochemical impedance microscopy for investigation of glucose oxidase catalyzed reaction.

In this research biointerface based on immobilized glucose oxidase (GOx) was evaluated by scanning electrochemical impedance microscopy (SEIM), which consisted of merged scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS). The gluconolactone, which is quickly hydrolyzed to gluconic acid, is produced during the enzyme-catalyzed glucose oxidation reaction. Gluconic acid formed above an enzyme-modified not-conducting plastic surface, was evaluated by EIS technique. A two electrode cell consisting of a scanning probe, which was based on 10 μm diameter ultramicroelectrode and stationary platinum counter/reference electrode was applied for the measurement. Locally measured solution impedance depends on the gluconic acid concentration close to the ultramicroelectrode surface and on the ion diffusion, which is hindered when the electrode is approaching close to the GOx-modified surface. EIS results were evaluated by applying an equivalent circuit consisting of elements representing solution resistance, double-layer capacitance, charge-transfer resistance and Warburg impedance. Solution resistance was calculated and showed to be dependent on the position of ultramicroelectrode. Also it was observed that the thickness of the conducting layer and gluconic acid concentration both are changing in time. The results indicate that here proposed SEIM technique could become a valuable tool for the investigation and characterization of enzyme-modified surfaces of biosensors and biofuel cells.