Impedance Characteristics of Gold-Extended-Gate Electrodes for Biosensor Applications

Electrochemical impedance spectroscopy technique has been used to study a variety of electrochemical phenomena on an electrode–electrolyte interface. The electrical characteristics of the electrode–electrolyte interface can be investigated using electrochemical impedance spectroscopy techniques for considering an extended-gate electrode of a field-effect transistor with an extended-gate electrode. In this paper, we present impedance characteristics between a reference electrode and gold electrodes with several dimensions fabricated on a glass wafer using electrochemical impedance spectroscopy technique. For this study, we have fabricated the circular gold-extended-gate electrodes with diameters of 0.1 mm, 0.2 mm, 0.5 mm, 1.0 mm and 2.0 mm. Then, the impedance which is changed by reaction of streptavidin onto biotin molecules was measured and compared for the different diameters. We have investigated that the variation of electron transfer resistance was greater than the interfacial capacitance in all cases, by immobilization of biotin or by reaction of streptavidin. We have also verified that the electrode with 0.2 mm in diameter showed the largest variation in electron transfer resistance and explained the reason. Additionally, we have considered about the field-effect transistor-based biosensor with extended-gate electrode in this study.