Date of Award

Fall 2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Mechanical and Aerospace Engineering

Committee Director

Ali Beskok

Committee Member

Shizhi Qian

Committee Member

Michael Stacey

Call Number for Print

Special Collections; LD4331.E56 G467 2013

Abstract

In recent years microfluidics has become one of the most commonly used tools to investigate cellular biology and to provide a platform for novel biomedical devices. Electrical Impedance Spectroscopy (EIS) was formulated as a non-invasive and label-fi.ee method to investigate the dielectric and the structural properties of materials. Since the early 20th century, EIS and Dielectric Spectroscopy have been applied to measure the dielectric properties of biological cells and tissues. Information about the cell membrane, cytoplasm and the nucleus can be extracted by dielectric spectroscopy. This thesis focuses on the applicability of the analytical models, in particular the Maxwell-Wagner Interfacial Polarization model, to extract the dielectric properties from cell suspensions where the height of the measurement chamber is comparable to the diameter of the cell. Two cases are investigated. The first case is comprised of a single standard human T-cell leukemia cell (Jurkat) being suspended in a measurement chamber. The chamber dimensions are varied to obtain the electrical impedance spectra of the cell in suspension. Physical models are fitted to the electrical impedance data to extract the dielectric properties of the cell. The errors in the estimation of the dielectric properties are compared to find the optimized chamber dimensions for single cell dielectric spectroscopy. Such a measurement chamber is also found to be stable to variations in the radius of the cell. Finally, the effect of changes in the vertical position of the cell on the estimation of the dielectric properties was investigated. It was observed that the estimated dielectric properties change significantly when the cells are moved close to the electrodes. The second case consists of a monolayer of Jurkat cells loaded into a measurement chamber whose height is comparable to the diameter of the cells. This simulation was accomplished using a parallel circuit approximation that matches the volume fraction and area of the electrodes while only simulating the impedance spectra of a single cell. These simulated impedance spectra were compared to corresponding effective medium model based impedance spectra and were found to predict the impedance spectra effectively. The sensitivity of the simulated impedance spectra to changes in the cell membrane permittivity and conductivity and the cytoplasm conductivity for different medium conductivities and volume fractions are investigated. Finally, the effect of the vertical distribution of the cells in the chamber is investigated. It was observed that the analytic models are only able to predict the impedance spectrum correctly if the cells are uniformly distributed within the chamber. The dielectric property estimation is inaccurate for all other cases.

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DOI

10.25777/h5n1-jx43

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