Wideband dielectrophoresis cytometers for studying single cells under starvation and thermal stresses
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Date
2019-07-22
Authors
Afshar Delkhah, Samaneh
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Abstract
Dielectrophoresis enables label-free and non-invasive cellular characterization and identification based on a cell’s distinctive dielectric properties. This thesis introduces a multi-frequency dielectrophoresis based technique which provides an approach for simultaneous determination of multiple dielectric properties of intracellular constituents. Here, a cytometer capable of dual-frequency DEP analysis of single cells while in-flow is developed. The application of the cytometer is demonstrated by simultaneous characterization of the membrane capacitance and cytoplasm conductivity of Chinese hamster ovary (CHO) cells. It is shown that the dual-frequency DEP cytometer enables identification of different dielectric related changes in a cell sample with multiple subpopulations. This application is demonstrated for CHO cells under starvation-induced apoptosis by using one frequency of the cytometer to identify viable and apoptotic cells within a sample and the other frequency to characterize their dielectric parameters. Results show that during starvation, membrane capacitance starts to decrease even before cells reach the apoptotic state. Results also show that cytoplasm conductivity initially remains constant and declines dramatically for early apoptotic cells.
In the second part of this thesis, a wide-band DEP cytometer capable of characterizing DEP response of single cells over the entire β-dispersion region is developed. Wideband DEP cytometry provides the Clausius–Mossotti factor (CMF) spectrum of a cell enabling development of a complete dielectric model for biological cells. It also provides the first and second crossover frequencies of the CMF spectrum allowing accurate identification of different cell types. The application of this system is demonstrated for CHO cells under starvation-induced apoptosis. Results show that transition of cells from viable to apoptotic state is accompanied by decrease in their CMF spectra over the β-dispersion region and subsequently an increase in their first crossover frequency as well as a decrease in their second crossover frequency.
The last part of this thesis focuses on using the DEP cytometer to investigate the impact of thermal stress on single CHO cells. It is observed that the membrane capacitance of cells decreases for a small increase in the temperature, suggesting alteration in morphological features of the cell membrane surface. It is also shows that the cell’s cytoplasm conductivity remains fairly stable over the hyperthermia temperature range and decreases at higher temperatures.
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Keywords
Biological cell, Chinese hamster ovary (CHO), di- electric spectroscopy, dielectrophoresis (DEP), interferometer, microfluidic, microwave Sensor, single cell