Date of Award

December 2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Engineering

First Advisor

Woo Jin Chang

Committee Members

Mohammad H Rahman, Yongjin Sung, Jorg C Woehl, Istvan G Lauko

Keywords

cross-over frequency, dielectrophoresis, oxide insulating layer, particle trapping, trap geometry, trap stiffness

Abstract

Dielectrophoresis (DEP) is an electrokinetic phenomenon in which neutral but polarizable particles suspended in a liquid medium experience a net movement due to a force generated from the permittivity difference between the liquid medium and the particles when subjected to a non-uniform electric field. We have developed a microfluidic particle trapping system using alternating current (AC) based DEP force for trapping spherical polymeric beads and biological particles. The DEP microfluidic device was constructed using orthogonal electrode configuration and fitted with three different basic geometric shapes, i.e., triangular, square, and circular. Effect of trap shape on particle trapping dynamics was quantitatively studied utilizing trap stiffness and particle trapping efficiency using negative dielectrophoresis. The analysis of three different trap shapes provides important insights to predict trapping location, the strength of the trapping zone, and optimized geometry for high throughput particle trapping. The effect of different operating conditions such as potential and the frequency of the applied electric field was also investigated. The dielectrophoretic cross-over frequencies of micro- and nano-sized polystyrene spherical particles were investigated as a model system. The cross-over frequency, where the DEP force reverses polarity, is a unique characteristic of the particles that varies based on their size, shape, structures, and polarization characteristics, e.g. conductivity, permittivity, and polarizability. Regarding the trap stiffness, the triangular shape trap was found strongest while the square shape trap was the weakest at the optimized DEP condition of 10 VP-P at 1 MHz with no-flow condition. However, the trapping efficiency of the square trap was found to be higher more than double compared to the triangular trap when tested in the flow-through condition. Characteristics of the microfluidic DEP device were examined through finite element simulation. This study was also extended to investigate the effect of oxide layer deposited on the metal electrode surface for reduction of electrochemical corrosion at the liquid-metal interface.

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