A Microfluidic Device for Impedance Spectroscopy

Recently, microfluidics has become a versatile tool to investigate cellular biology and to build novel biomedical devices. Dielectric spectroscopy, on the other hand, allows non-invasive probing of biological cells. Information on the cell membrane, cytoplasm, and nucleus can be obtained by dielectric spectroscopy provided that appropriate tools are used in specific frequency ranges. This dissertation includes fabrication, characterization, and testing of a simple microfluidic device to measure cell dielectric properties. The dielectric measurements are performed on human T-cell leukemia (Jurkat), mouse melanoma (B16), mouse hepatoma (Hepa), and human costal chondrocyte cells. Dielectric measurements consist of measuring the complex impedance of cell suspensions as a function of frequency. Physical models are fitted to raw impedance data to obtain parameters for cell compartments. The dielectric measurements are further supported by dielectrophoresis (DEP) experiments. Crossover frequency, which is the applied frequency when the DEP force is equal to zero, is recorded for cells by changing buffer conductivity. Cell membrane properties are also estimated from the crossover frequency measurements. Sensing capability of the microfluidic device to external stimuli is tested with Jurkat, chondrocyte, and Hepa cells. Jurkat and chondrocyte cells are suspended in buffers with changing osmolarity, and cell membrane properties are probed. Results indicate osmotic swelling of Jurkat cells. Interestingly similar changes were not observed in chondrocyte cells. Ion efflux from Hepa cells is quantified by conductivity measurements, and ionic flux from an average cell is calculated. Finally, a separability parameter is introduced and plotted for Jurkat and B16 cells pair. The separability parameter is based on the difference of two cells\u27 Clausius-Mossotti factors, which is a function of the dielectric parameters of the cells, field frequency, and buffer conductivity. Using the separability maps one can choose the optimum conditions for cell separation using DEP