Integrierte Impedanzspektroskopie aerober Zellkulturen in biotechnologischen Hochdurchsatzscreenings

  • Integrated impedance spectroscopy of aerobe cell cultures in high throughput screenings

Hofmann, Mirko; Mokwa, Wilfried (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2009)
Dissertation / PhD Thesis

Aachen, Techn. Hochsch., Diss., 2009


The presented work focuses on the development, fabrication and characterisation of electrical sensors to measure dielectrical properties of biological cell solutions during fermentation processes. For this, two different sensor concepts are tested and compared: galvanically decoupled sensors and sensors with four-electrode-configuration. All sensors are fabricated on flexible polyimide foils with processes based on MEMS-technology. In order to characterise the developed sensors physically, all sensors are tested in KCl-solutions of different conductivity. The conductivity varies in a range of 3 mS/cm up to 19 mS/cm. Furthermore, impedance measurements in cell solutions are carried out during fermentation processes. All these measurements are compared and interpreted with postulated theoretical models. Beside the electrical also the material properties of the fabricated electrodes are of interest. Therefore, electrodes with pure platinum surfaces are compared to electrodes covered by a thin iridiumoxyde layer. By a simple electrical pre-conditioning of the iridium-electrodes the electrochemical impedance of the electrode surface can be reduced significantly compared to those made out of pure platinum. Measurements in high concentrated cell-solutions and during fermentation processes show the applicability of the developed sensors for the online monitoring of biological processes and cell growth. The cell culture used in this work is the yeast culture Hansenula Polymorpha. Even at low concentrations of less than 15 g/l the growth of these cells can be monitored clearly. In addition to this, tests with bacteria Escherichia Coli are carried out in complex TB-medium (terrific broth medium). As the maximum frequency is not higher than 10 MHz in this work it is not possible to detect the whole frequency-step of the beta-dispersion of the small bacterial cells (< 2 µm). Therefore, the capacitive measurement signal is not a clear indicator for the biomass. Changes in conductivity due to the metabolism or morphological changes of the cells can influence the measured signal of the electrical properties as well. In this work the feasibility of integration of impedance measurement systems in standard microtiter plates is shown. The information achieved by the electrical measurements is suited for monitoring and characterising fermentation processes of aerobe cell cultures even in small volumes of less than 200 µl.


  • Chair of Materials in Electrical Engineering I and Institute of Materials in Electrical Engineering [611510]