Electrochemical impedance spectroscopy in microfluidic devices for kinetic analysis of binding reactions
Lazar, Jaroslav; Schnakenberg, Uwe (Thesis advisor); Knoch, Joachim (Thesis advisor)
Dissertation / PhD Thesis
Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020
Novel sensors for measuring protein binding using electrochemical impedance spectroscopy (EIS) were developed in this work. Three development steps were carried out in order to successfully perform EIS measurements. First, the stability of the EIS measurements in the presence of potassium hexa-cyanoferrate (HCF) in the electrolyte was examined. It has been shown that the impedance signal of a gold electrode exhibits significant drift behavior in the presence of HCF, which makes reproducible EIS measurements difficult. The drift is caused on the one hand by adsorption and desorption of chlorine ions and on the other hand by etching gold electrodes by cyanide ions. The drift dependency can be minimized either by using smoother electrode surfaces or by using a non-Faraday electrolyte based on saline solution buffered with phosphate. Second, a flow-over sensor with six individually controllable interdigital microelectrodes, which are integrated in microfluidic channels, was developed. The immobilization of the prostate-specific antigen on the gold electrodes was successfully demonstrated with EIS. The previous results of the stability study were confirmed. The use of HCF leads to a high signal-to-noise ratio, but the stability of the measurement was not satisfactory. In addition, the sensor setup was successfully used for the detection of lectin binding to two glycoprotein polymer topologies using EIS. It was found that the electrical double-layer capacitance and electrical double-layer resistance in particular are measured at low frequencies and the binding characteristics of the lectin to and into the glycopolymer at higher frequencies. Third, a combination of EIS with localized surface plasmon resonance (LSPR) was investigated. For this purpose, a novel microfluidic EIS - LSPR flow sensor system based on a nanoporous filter membrane was developed. The measurements showed for the first time that the EIS signals originate from the sensor surface depending from the applied frequency, and the LSPR signals from the nanohole area. This EIS-LSPR sensor structure, which simultaneously enables an optical and an electrical measurement of binding kinetics on gold surfaces, offers for the first time the possibility of differentiating the EIS signal through correlation be-tween spatial origin and the excitation frequency.