Cell sorting and Separation via High Frequency Dielectrophoresis
Authorhadady gharehghieh, Hanieh
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The primary research goal of this dissertation was to examine high-frequency (20-80 MHz) dielectrophoresis (DEP) to separate and sort cells based on differences in cytoplasmic conductivity and other interior features. Microalgae were the target for the majority of this study due to the ease in which cytoplasmic lipid content can be controlled and measured. The primary outcome of this dissertation is that increases in lipid content within the microalgal cell will change the high-frequency DEP response due to a decrease in cytoplasmic conductivity. In particular, the upper crossover frequency (i.e. a high-frequency at which no DEP-induced motion is observed) was shifted to lower frequencies as the amount of lipids within the cell increased. Therefore, a range of frequencies exist where cells with high lipid content and low lipid content can be separated since the DEP-induced motions will be in opposite directions.Extensive analytical, numerical, and experimental studies of high-frequency DEP have been carried out to determine the correlation between the lipid content of a microalgal cell and the cell's high-frequency DEP response. Hollow liposomes were used to confirm the single-shell model where the upper crossover frequency is dictated primarily by the dielectric properties of the cytoplasm. Chlamydomonas reinhardtii was cultured under stressful nitrogen free conditions and the lipid content was quantified via fluorescent microscopy. The microalgae cells with different lipid amount were stationary separated at 42 MHz where upper crossover frequency of high lipid cells was shifted to 25 MHz. The upper crossover frequency of the low lipid cells was a function of electric conductivity of the culture medium. A continuous-flow screening device that can sort microalgae on the basis of lipid content was designed and built for the purpose of exploring one potential application of this technology. Two distinct strains, mutant (MU) and wild type (WT) C. reinhardtti, were cultured to provide microalgae with different lipid amounts (MU accumulates half the lipid as WT). This device enabled separation of the microalgae cells with different lipid content at 50 MHz with 1000 cells/s throughput and 74% enrichment of the high lipid cells population (WT). Lastly, flow cytometry was used to perform a sensitivity analysis for separation via high-frequency DEP in continuous-flow microfluidic device. The goal of this last study was to quantify high-frequency DEP separation based on lipid content.