Abstract

The increasing demand for efficient separation processes of micron-sized particles, including microorganisms, highlights the importance of developing low-cost, non-labor-intensive, and time-efficient techniques. Insulator-based electrokinetic (iEK) systems have proven to be a practical alternative to bench-scale methodologies such as centrifugation and membrane filtration. Several studies have reported the separation of microparticles by employing direct current (DC) voltages. However, all of them have overlooked the phenomenon of nonlinear electrophoresis (EPNL) and its role in the electrokinetic migration of particles. This study combines mathematical modeling and experiments to extend the capabilities of iEK systems. This dissertation has four aims: (1) to separate microparticles and cells using iEK systems, (2) to improve iEK device designs for charge- and size-based separation, and (3) to employ EPNL for reversing migration order of analytes in EK separations, and (4) to develop an empirical equation for particle retention time based on particle characteristics, microdevice features, and applied DC voltages, with a focus on EPNL. In the first aim, electrokinetic separations of mixtures of micron-sized particles, bacteria, and yeast cells was conducted, achieving the challenging separation of highly similar microparticles, a significant contribution to the field. By combining modeling and experimental approaches, two distinct types of microparticles (~5 µm) with a small zeta potential difference of 3.6 mV were successfully separated. The promising findings from this study paved the way for separating microorganisms even in the same domain and genus. Also, this aim presents cell separation in iEK systems where three different binary mixtures of cells (Escherichia coli vs. Saccharomyces cerevisiae, Bacillus cereus vs. Saccharomyces cerevisiae, Bacillus cereus vs. Bacillus subtilis) were separated, with the difficulty level increasing in each subsequent separation. The second aim is to improve the device design for separating a more complex sample, a tertiary sample of microparticles. By combining mathematical simulations and iEK separation experiments, iEK systems were improved for more efficient charge-based and size-based separation. In this study, two configurations were selected for the effective separation of complex samples. The third aim is to reverse the migration order of analytes by altering the electrokinetic regime in electrokinetic microsystems by changing the applied DC voltage. In this study, a charge-based separation of particles was performed in the linear electrokinetic regime, and within the same microdevice, a size-based separation was performed under the nonlinear electrokinetic regime, marking the first reported reversal in elution order in iEK systems. Also, in a different study, the improved design found in Aim 2 was tested to reverse the elution order cells of the same domain and genus but different strains (two strains of Saccharomyces cerevisiae). The successful reversal of elution order in two strains of Saccharomyces cerevisiae highlighted the efficiency of the improved design. Aim four focuses on gathering the findings obtained in Aims 1 to 3 and analyzing the information to develop correlations based on the electrokinetic characteristics of particles and device configuration to predict parameters such as retention time in the separation of (bio)particles. This aim introduces a method to predict particle retention time in iEK systems under linear EK conditions while considering EPNL, particle properties, electric fields, and microdevice features. Experiments with eight distinct microparticles (3.6–11.7 µm, ~-20 mV, and ~-30 mV zeta potentials) were conducted in three iEK microdevices: a device with asymmetrical insulating posts, one with symmetrical insulating posts, and one without posts (postless). The microparticle retention times tR,e were measured at 400–1450 V, leading to three empirical equations for particle velocity, incorporating linear and nonlinear effects. Validation with control particles showed a fair prediction error, highlighting the equations' potential for designing particle separations in iEK systems. This dissertation highlights the capability of iEK systems to achieve highly discriminatory separations of mixtures containing micron-sized entities, including microparticles and cells.

Library of Congress Subject Headings

Electrophoresis; Electrokinetics; Labs on a chip; Filters and filtration

Publication Date

5-13-2025

Document Type

Dissertation

Student Type

Graduate

Degree Name

Biomedical Engineering (BS)

Department, Program, or Center

Biomedical Engineering

College

Kate Gleason College of Engineering

Advisor

Blanca H. Lapizco-Encinas

Advisor/Committee Member

Tom Gaborski

Advisor/Committee Member

Vinay Abhyankar

Campus

RIT – Main Campus

Plan Codes

BMECHE-PHD

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