Doctor of Philosophy
James C. Hwang
For the first time, the impedance spectrum of live Jurkat T-lymphocytes human cells was characterized in a single sweep spanning six decades of frequency from 9 kHz to 9 GHz. The ultrawide bandwidth bridged the traditional impedance spectroscopy at kilohertz to megahertz frequencies with the recently developed microwave dielectric spectroscopy, which can probe the cell interior without being hindered by the cell membrane. Based on the measured scattering parameters and a simple cell model, an equivalent circuit of four nondispersive elements, including membrane resistance, membrane capacitance, cytoplasm resistance, and cytoplasm capacitance, was extracted and found sufficient to explain the so-called β relaxation over the frequencies measured. The extracted cell parameters were in general agreement with the literature. However, the presently extracted membrane capacitance of 0.4 pF and cytoplasm resistance of 0.75 MΩ are on the low and high end of the literature, respectively. This could be explained by having separated out the shunt effects of the membrane resistance and cytoplasm capacitance, respectively. In fact, the present membrane resistance and cytoplasm capacitance, at 2.8 MΩ and 10 fF, respectively, are believed to be more reliable due to the low-conductivity solution and the microwave frequency used.
Meanwhile, sensitivity analysis was carried out for extracting lumped cell characteristics such as membrane resistance and cytoplasm capacitance from the scattering parameters. The scattering parameters were measured on a coplanar waveguide with a Jurkat cell trapped by dielectrophoresis either in a series or shunt configuration. The sensitivity analysis validated our previous empirical observation that the insertion loss of a series-trapped cell and the return loss of a shunt-trapped cell were most sensitive to the cell impedance. Additionally, the membrane resistance and cytoplasm capacitance were most sensitive to low- and high-frequency scattering parameters, respectively.
Furthermore, the dissertation presents a novel in situ single-connection calibration using biocompatible solutions, which is demonstrated in single-cell characterization from 0.5 GHz to 9 GHz for the first time as well. The characterization is based on quickly trapping and detrapping the cell by dielectrophoresis on a coplanar waveguide (CPW) with a small protrusion in one of its ground electrodes, which doubles as the calibration standard when covered by different liquids. Consistent with theoretical analysis, the difference in the transmission coefficient increases with increasing frequency and is generally smaller than the difference in the reflection coefficient. With improved accuracy and throughput, the calibration technique may enable broadband electrical characterization of single cells in a high-speed cytometer.
Ma, Xiao, "Dielectric Spectroscopy of Biological Samples" (2019). Theses and Dissertations. 5682.