Single cell analysis and quantitative modelling of ion concentrations and dielectric properties of Chinese hamster ovary cells
The dielectric properties of biological cells are indicators of their physiological states. Cells dielectric properties change in response to physiological changes such as stem cell differentiation, the transition of cancerous to multidrug-resistant cancer cells, and apoptosis. Ion concentrations make an important contribution to the dielectric response of cells in these processes. Single-cell dielectric analysis techniques can be used to detect these events and monitor the dielectric response of cells. However, in order to link the dielectric response of cells to their physiological states, a quantitative model of ion fluxes is required. In this thesis, a quantitative model of ion concentrations and hence cytoplasm conductivity for Chinese hamster ovary (CHO) cells, which are used in 70% of all biopharmaceuticals, is presented. A flux-based assay has been used to study ion channel and Na+/K+ ATPase pumps activity and determine CHO-specific model parameters. In order to validate the model, temporal changes in cytoplasm conductivity of pump inhibited CHO cells using 5 mM Ouabain are monitored using a dielectrophoresis cytometer. The model predictions match the experimentally observed temporal changes in cytoplasm conductivity of pump inhibited cells. The second part of this thesis focuses on monitoring the cytoplasm conductivity of CHO cells during nutrient deprivation since the nutrient level directly influences the activity level of Na+ /K+ ATPase pumps and cytoplasm conductivity. Employing single-cell dielectrophoresis, the cytoplasm conductivity of nutrient-deprived and nutrient-reintroduced cells are monitored. A minimum cytoplasm conductivity of nutrient-deprived cells that maintain the ability to restore to the normal viable level when nutrients are reintroduced is determined, 0.3 S/m. The developed quantitative model is also used to predict the minimum cytoplasm conductivity of nutrient-deprived cells with the ability to recover to the normal viable state, and the predicted value is in agreement with the experimental results. In the last part of this thesis, an optical dual-source DEP cytometer capable of high throughput characterization of single CHO cells is developed. The developed optical cytometer provides the Clausius Mossotti factor spectrum of viable CHO cells. This system is also capable of quantitative characterization of 10 μm-diameter polystyrene spheres with more than 300 particles per second analysis rate.
Dielectric properties, Dielectrophoresis, Single cell analysis, Chinese hamster ovary cells, Microfluidic, Quantitative model