Models and ultra-sensitive apparatus for electronic single cell analysis

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Cells are dynamic electronic materials that change electronic state in response to environmental pressures. There have been many demonstrations that cells exhibit dielectric changes that coincide with important physiological changes such as the differentiation of stem cells, the development of multi drug resistance (MDR) in cancer cells, and programmed cell death (apoptosis). Single cell measurements of the dielectric response can identify dielectric sub-populations and temporal changes to these sub-populations that are not possible with common bulk probes. The proposed research program will derive quantitative models of the relationship between electronic and physiological changes in cells and also to produce instrumentation with superior ability to detect these dielectric changes in single cells. The work will focus on the use of dielectrophoresis (DEP) in a flow system that bring cells from a reservoir to the analysis region, making the analysis of a large number of cells practical in a reasonable time frame. In collaboration with G. Bridges I have developed a flow based single cell DEP analysis instrument. It can detect apoptosis by sensing the modified polarization that results from a drop in intracellular potassium, concentrations. Using a microwave interferometer in a differential detection approach, this DEP cytometer detected apoptosis in Chinese Hamster Ovary (CHO) cells. I propose to investigate some of the basic mechanisms of dielectric changes in cells using compounds that are well known to inhibit or activate specific biochemical pathways that will impact the dielectric properties of the cell. For example, Ouabain inhibits the operation of the K+Na+ pumps in the cell causing changes to the ion concentrations within the cell and hence its dielectric properties. Other compounds control the pores that allow ions in and out of the cells. Some of these compounds may also prove useful as “dyes” that provide a specific dielectric read out. In some of the physiological events outlined above these pumps and pores have been hypothesized to play a major role. The proposed research will measure the impact of these compounds and derive mathematical models that relate the inhibition of specific processes to dielectric changes. The small volume of cells makes single cell dielectric measurements very challenging. New microwave interferometer designs and DEP actuation methods will be used to lower the dielectric detection limits. The goal of the work is to detect dielectric changes (Clausius Mossotti Factor) of less than 5% in a single cell. The HQP from this interdisciplinary research program will gain skills for many career paths. This group is one of the few with the collaborations and tools to undertake this research. This work will impact users and researchers of bulk dielectric and single cell dielectric measurements and provide desperately needed new tools for single cell biophysiology.