Graduation Year

2007

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Electrical Engineering

Major Professor

Shekhar Bhansali, Ph.D.

Keywords

Biosensor, Bioimpedance, Cell-based assays, Whole cell assays, Cell substrate sensing

Abstract

The objective of this research is to develop fundamental understanding of cell-substrate (CS) and cell-cell (CC) interactions in the culture space for time evolving cell cultures. Space resolved CC and CS interactions are important indicators of cell-density distribution, localized cellular behavior, and multiple cell-layers which are differentiators of normal and abnormal cell behavior. In this research, CS and CC interactions and the variations therein due to a) Cell growth, 2) cell-drug interaction, and 3) effect of Cytotoxin were studied using multielectrode, multi-frequency Electrochemical Impedance Spectroscopy (EIS). Contemporary impedance based methods sense either CC or CS interaction as a space averaged macroscopic quantity. A major contribution of this research is that, both CC and CS interactions are recorded and analyzed with spatio-temporal resolution. This research led to the development of an automated cell culture monitoring system, namely, CellMap.

A planar eight electrode sensor was fabricated on a glass substrate and interfaced with a switching circuit. The switching circuit sequentially selects consecutive electrodes upon input of a 5V trigger pulse which is generated by the frequency response analyzer at the end of each frequency scan, thereby facilitating automated switching and recording of multielectrode dataset. Calibration standards and protocols were developed to null the channel parasitics of individual channels. A set of eight impedance measurements for eight electrodes constitutes a "frame". Frames are recorded at regular time intervals over the desired course of time. Impedance mapping of adhesion, spreading, motility and detachment of OvCa429 ovarian cancer cells was performed over a period of 70 hours. The cell-layer resistance, which indicates cell-cell contact, increased as a function of time until confluence, and decreased thereafter due to cell death and detachment.

This was also confirmed by optical microscopy observations. Similarly, the cell layer Constant Phase Element (CPE) parameters, which were found to correlate well with cell density distribution, also increased as a function of time until confluence and decreased thereafter. Additionally, the cell-growth mapping revealed that the CellMap system is able to resolve non-uniform cell distributions in the culture space, which may be useful in differentiating between normal and pathological cells.

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