Design and characterization of electrochemical impedances biosensors for microfluidic devices

Abstract

In the recent years, there has been a merger of microelectronics and biological sciences to develop what are called “Micro Total Analysis System ($μ-TAS$)”. To enhance the portability and disposability of microfabricated analysis systems, much work has been directed increasingly towards the development of on-chip detection for the direct interrogation of the electrical properties and behavior of biological species. In this thesis, electrochemical impedance sensors have demonstrated in terms of the feasibility of label-free deoxyribonucleic acid (DNA) detection and the frequency characteristics and design rule of coplanar impedance sensors. Glass-based microchannel chips were fabricated using micromachining technology, and Pt thin-film microelectrodes, as coplanar impedance sensors, were integrated on them. In chapter 4, DNA detection method based on dielectric properties was described. From capacitance-frequency measurements at various interelectrode distances and ionic concentrations, a significant difference between the deionized (DI) water and the TE buffer (tris-HCl + ethylenediaminetetraacetic acid (EDTA)) was observed. This was discussed from the viewpoint of interfacial phenomena, such as the electrical double layer and Faradaic reactions, the dielectric constant related to the conductivity, and the capacitance inversely proportional to the interelectrode distance. From the nondependence of capacitance on interelectrode distance in the low-frequency region of the TE buffer, we focused on the electrode-electrolyte interface and explained the behavior observed using the double layer model and Fradaic reactions. The addition of ions and molecules increased capacitance due to the diffusive mobile layer and the Faradaic reaction at the electrode-electrolyte interface. The addition of DNA molecules (10ng/㎕) resulted in an increase in capacitance and dielectric loss in the TE buffer at low frequency. It is feasible to use dielectric properties for rapid and dir...