Date of Award

2023

Document Type

Open Access Master's Thesis

Degree Name

Master of Science in Chemical Engineering (MS)

Administrative Home Department

Department of Chemical Engineering

Advisor 1

Adrienne R. Minerick

Committee Member 1

Caryn Heldt

Committee Member 2

Rebecca G. Ong

Abstract

Electrokinetic microfluidics is a versatile technology utilized within lab on a chip (LOC) devices for diagnostic and analytical applications; advantages include reduced resource demands, flexibility, and simplicity of use. Dielectrophoresis (DEP) is a precision nonlinear electrokinetic tool utilized within microfluidic microdevices to induce polarization and control bioparticle motions for applications that range from hemoglobin separations to cancer cell isolation and detection. Despite promising results, undesired side phenomena can occur in electrokinetic systems which impede reproducibility and accuracy. These unfavorable phenomena have not been comprehensively explored in the literature. Prior preliminary research suggests the fundamental phenomena originate from microelectrodes utilized in the electrokinetic systems whose surface reactions drive ion byproducts into the adjacent medium. The medium variations can thus affect the cell’s viability as well as bioparticle structure and function.

The research results reported in this thesis focuses on characterizing pH gradients in an aqueous solution under nonlinear electric fields generated via non-uniform electrode geometries to more fully characterize microdevice-imposed artifacts on cells in clinical diagnostic devices. In addition to exploring frequency dependence, this work also explores the use of a hafnium dioxide (HfO2) dielectric coating over the electrodes as a strategy to eliminate the undesired reactions.

Results revealed pH changes in the frequency range of 0.2 to 1.4 times the electrode charging frequency at a constant electric field of 0.07 Vpp/ in devices with T-shaped and star-shaped electrode geometries. The pH change was quantified with respect to time, applied frequency, electrode geometry, as well as uncoated and HfO2-coated electrodes. This work provides insight that the pH changes correlate directly with electric field density gradients and frequency. Further, results demonstrate that HfO2 is a viable tool to impede the surface reactions driving pH changes at frequencies at and above the electrode charging frequency, but the HfO2 coating and impeding properties rapidly deteriorate at lower frequencies.

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