Electrical Impedance Spectroscopy and Its Application in the Study of Electrochemical Sensors

Abstract

Electrochemical methods are widely used in characterisation of catalytic properties and analytical application of the electrode materials. Study of electrical impedance spectra in electrochemistry, electrochemical impedance spectroscopy (EIS), is a technique frequently used as a supplementary method in the study of electrical properties of electrochemical sensors. However, the interpretation of the EIS results requires more complex knowledge about the electrochemical process, for instance the mechanism of the reaction, morphology and characterization of the electrode material [1]. Among various electrochemical sensors, the glucose ones represent majority of the sensors industry and cyclic voltammetry, chronoamperometry and EIS are used for complex studies of their electrochemical properties. Currently, the scientific community makes an effort to overcome the drawbacks of commercial glucose sensors and to develop nonenzymatic kinds based on the direct oxidation of glucose on the electrodes. Various electrode materials were used to achieve specific electroanalytical properties, such as low limit of detection, wide linear concentration range, sensitivity, and reproducibility [2]. Gold and titanium dioxide represent two different types of materials with diverse electrical properties. Gold as an electrode material displays great conductivity and electrocatalytical activity toward the glucose oxidation. As a transition metal, it displays an ability to attain multiple oxidation states and to absorb electroactive species. Possibility to detect glucose in neutral media is the great advantage because it makes predisposition for development of the continuous glucose sensor. Gold also displays wide linear concentration range and good reproducibility. Titanium dioxide is a multifunctional material which due to its semiconductive nature got an application in electronics and electrochemistry. TiO2 nanotubes are widely used in energy generation, accumulation and saving. In case of electrochemical sensors TiO2 nanotubes are suitable as a substrate because of its great surface area [3]. Electrochemical impedance spectroscopy was used to study the electrochemical properties of the gold and titanium dioxide as potential electrode materials for glucose determination. Even if gold and TiO2 display different electrical properties and mechanisms of interaction with glucose, the EIS measurements display similar results. For the gold electrodes the current response increases linearly with the glucose concentration. Process of glucose oxidation begins with an adsorption of the molecule on the gold surface followed by electrochemical oxidation. In the case of titanium dioxide, the current response decreases in the presence of glucose in comparison with cyclic voltammogram of the blank sample. Current response decrease is probably connected with the formation of the covalent bond between glucose and TiO2. In this study EIS enables the usage of different (in principle) interaction mechanisms between the electroactive material surface and glucose for the similar purpose – detection and its quantitative determination. Acknowledgement: This work was supported by the projects VEGA 1/0074/17 of the Slovak Scientific Grant Agency, APVV-16-0029 of the Slovak Research and Development Agency, VVGS-PF-2018-794 and VVGS-PF-2018-795 of Pavol Jozef Šafárik University in Košice, Slovakia.