Date of Award

8-2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Bioengineering

Advisor

Zhang, Guigen

Committee Member

Gao , Bruce Zhi

Committee Member

Xuan , Xiangchun

Abstract

Dielectrophoresis has long been studied and utilized for the manipulation of microscale particles in solution. This phenomenon is due to the induced polarization of dielectric particles subjected to an electric field. When the field is also inhomogeneous in terms of the distribution of its strength through space, the polarized particles move and come to rest in certain areas due to the relationship between their and the solvent's relative permittivities. If the electric field is homogenous, such as within a parallel plate capacitor, the particles are polarized according to their permittivity and the field's frequency, but they will not move.
These relationships have been exploited for many lab-on-a-chip applications such as positioning cells for tissue engineered structures, separating live cells from dead ones, or separating cells of different types. Some of these systems also employ microfluidics in order to add another level of control, increasing the degrees of freedom when manipulating microparticles.
The goals of this study are to develop and experimentally characterize a low power setup for moving and aligning particles using dielectrophoresis, to perform experiments to quantify the effect of conductivity on the dielectrophoretic force, to analyze and quantify the out of plane force, and to use these experimentally determined relationships to create more accurate theoretical models of dielectrophoresis processes using COMSOL Multiphysics software.
The first step in this process involves the creation of a technique to perform dielectrophoresis using relatively low power. This requires the use of a very thin, durable membrane to separate the particles in solution from the field generating electrodes. The use of this very thin membrane, much thinner than those used in previous studies,1 has revealed a much more complete picture of the behavior of microparticles in response to the forces present during dielectrophoresis. A more complete picture of reality has the potential to lead to the creation of more accurate models and descriptions of the underlying physics.
Once this novel setup was shown to produce consistent results, the studies began. These consisted largely of frequency sweeps at constant voltages and voltage sweeps at given frequencies, similar in basic method to studies which have been peformed to analyze dielectrophoretic systems in the past. No flow is present in the particle suspension for the majority of these studies. This constraint, coupled with the insulating layer over the electrode theoretically limits the forces present to principally those elicited by dielectrophoresis.
With this setup it was found that polystyrene beads were arranged into parallel lines of pearl chains in the spaces between interdigitated electrodes with sufficient predictability that models of this phenomenon could be created and aligned with reality. In addition to these in-plane forces governing the formation of pearl chains, the out of plane forces were also analyzed and modeled. In the case of negative dielectrophoresis, this is the force lifting the beads off of the electrode surface. The effect of media conductivity on particle alignment and levitation has also been analyzed using this setup. In addition to these experiments with polystyrene beads, this setup has also been shown to manipulate cells under low media conductivity conditions.
It is important that the forces and physical relationships involved in these insulated dielectrophoresis setups are better understood, so that such techniques can be more precisely and predictably implemented for lab-on-a-chip and tissue engineering applications.

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