Digitale Mikrofluidiksysteme zur Charakterisierung von Immobilisationsvorgängen von Biomolekülen mittels elektrochemischer Impedanzspektroskopie

• Digital microfluidic systems for the characterization of immobilization processes of biomolecules by means of electrochemical impedance spectroscopy

Kremers, Tom; Schnakenberg, Uwe (Thesis advisor); Knoch, Joachim (Thesis advisor)

Aachen : RWTH Aachen University (2021)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2021

Abstract

Digital microfluidic (DMF) systems utilizing the electrowetting effect to manipulate discrete droplets by modulating the contact angle by applying electric fields. This enables droplet transport across hydrophobic surfaces. The droplets and the required electrodes are separated by a hydrophobic and an insulating layer. Hence, these systems are called electrowetting on dielectric (EWOD) systems. Small droplets in the range of nano- to picoliter can be created, transported, merged with other droplets and mixed via EWOD. The motion patterns of the droplets can be programmed by individually addressing of electrodes. This allows the application of EWOD systems in different research fields and industrial applications (e.g. polymerase chain reaction (PCR) for biomedical diagnostics).In this work, two EWOD platforms are developed - a labview and mechanical relais based platform and a portable EWOD platform. The portable EWOD platform PortaDrop provides the ability to manipulate droplets and to carry out electrochemical measurements without additional external equipment. PortaDrop uses a Raspberry Pi as the central control unit of the EWOD platform for the first time. Hence, the integration of additional external measurement devices is possible and basically implemented. As an example of application, an EIS sensor is embedded into the EWOD platform. For enhanced stability of the measurements, the counter- and reference electrodes are coated with the conducting polymer polypyrrole:polystyrene sulfonate (PPy:PSS). The electrical properties of the PPy:PSS-layers are determined by EIS. Therefore, the electrode/electrolyte junction of the electrodes is measured in a salt containing solution. For the first time, the measurements are fitted to an electric equivalent circuit and the evolution of the circuit elements is associated with the mechanism of growth of the layers. The developed EIS sensor is finally used for monitoring the successful glycosylation of a neo-glycoprotein (NGP) throughout a fucosyltransferase (FucT) longitudinally enabling the extraction of the binding constants.This thesis is structured as follows: First, the basics of DMF and EIS as well as conducting polymers are presented followed by a summary of the state of the art. Subsequently, the development of necessary fabrication processes for the electrode substrates including the integrated EIS sensor and the development of the hard- and software for both EWOD platforms is described. Subsequently, these developments are characterized and discussed. The application of the developed components and systems is shown my monitoring immobilization processes of biomolecules via EIS. The thesis is closed with a conclusion and an outlook is given.

Institutions

• Chair of Micro- and Nanosystems and Institute of Materials in Electrical Engineering [612510]