Date of Award

5-2010

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Mechanical Engineering

Advisor

Xuan, Xiangchun

Committee Member

Miller , Richard S

Committee Member

Ma , Lin

Abstract

With the recent advancement in micro-fabrication technology, lab-on-a-chip devices have been developed in order to perform biological analysis through cell manipulation. Microchannels used in these lab-on-a-chip devices have been demonstrated to accurately perform many different cell manipulation techniques such as focusing, separation, trapping, and lysis. Although there are many methods available for these techniques, electrokinetics has been rapidly gaining popularity due to the simplicity of application and removal of the need for in channel micro-structures. This thesis studies the use of electrokinetic flow and accompanying phenomena in various structured microchannels to perform focusing, separation, trapping, and lysis of cells. Three related projects were conducted in series.
First, a parametric study of the focusing of yeast cells using negative dielectrophoresis in a serpentine microchannel was studied. Focusing cells into a single stream is usually a necessary step prior to counting and separating them in microfluidic devices such as flow cytometers and cell sorters. This work demonstrated a sheathless electrokinetic focusing of yeast cells in a planar serpentine microchannel using DC-biased AC electric fields. The concurrent pumping and focusing of yeast cells arose from the DC electrokinetic transport and the turn-induced AC/DC dielectrophoretic motion, respectively. The effects of electric field (including AC to DC field ratio, and AC field frequency) and concentration (including buffer concentration and cell concentration) on the cell focusing performance were studied experimentally and numerically. A continuous electrokinetic filtration of E. coli cells from yeast cells was also demonstrated via their differential electrokinetic focusing in the serpentine microchannel.
Next, negative and positive dielectrophoretic focusing were also studied in their application to particle separation in a serpentine microchannel. This work first demonstrated negative and positive dielectrophoretic focusing of by changing only the electric conductivity of the suspending fluid. Due to the channel turn-induced dielectrophoretic force, particles were focused to either the centerline or the sidewalls of the channel when their electric conductivity was lower (i.e., negative DEP) or higher (i.e., positive DEP) than that of the fluid. These distinctive dielectrophoretic focusing phenomena in the serpentine microchannel were then combined to implement a continuous separation between particles of different sizes and electric conductivities. Such separation eliminates the fabrication of in-channel microelectrodes or micro-insulators that are typically required in DEP-based separation techniques.
Lastly, red blood cells were used to study cell lysis and trapping in a microchannel constriction. Cell Lysis is an important step in the analysis of intracellular contents. Electrical lysis of red blood cells was demonstrated in a hurdle microchannel using a low continuous DC-biased AC electric field amplified by channel geometry. Trapping of cells was also demonstrated using this DC-biased AC electric field, and the transition between trapping and lysis of red blood cells in this microchannel was demonstrated by simply adjusting the applied DC voltage. Further, these phenomena were used in conjunction to demonstrate the separation of Leukemia cells from red blood cells.

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