An electrical microcytometer for portable blood analysis in global health applications

Watkins, Nicholas

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https://hdl.handle.net/2142/32048 Copy

Description

Title

An electrical microcytometer for portable blood analysis in global health applications

Author(s)

Watkins, Nicholas

Issue Date

2012-06-27T21:30:25Z

Director of Research (if dissertation) or Advisor (if thesis)

Bashir, Rashid

Doctoral Committee Chair(s)

Bashir, Rashid

Committee Member(s)

• Cunningham, Brian T.
• Jain, Kanti
• Rodriguez, William

Department of Study

Electrical & Computer Eng

Discipline

Electrical & Computer Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Lab on a chip
• point of care diagnostics
• microfluidics
• impedance cytometry
• Acquired immunodeficiency syndrome (AIDS)
• Human immunodeficiency virus (HIV)

Abstract

For three decades the AIDS (Acquired Immune Deficiency Syndrome) pandemic has killed millions and currently affects tens of millions around the world. It has especially crippled resource-poor regions in the world such as sub-Saharan Africa, which contains two-thirds of the world's people living with AIDS. Antiretroviral therapy (ART) to combat the human immunodeficiency virus (HIV) has become more accessible to patients in these regions over the past several years, and has shown to improve the quality of their lives. However, the lack of objective diagnostics—CD4+ T lymphocyte counts—to determine when to start ART and to monitor its success hinders the effective use of treatment in these regions. The industry standard of flow cytometry to obtain CD4+ T cell counts is too taxing on the debilitated healthcare infrastructure of undeveloped nations because of its high cost, technical demands, and lack of portability. Therefore, there is an urgent need to develop a portable, robust, and affordable point-of-care (PoC) CD4+ T cell counter that can reach all HIV/AIDS patients, regardless of geography or socio-economical situation. This dissertation addresses this great need through investigation of a miniaturized, portable PoC platform that can provide CD4+ T cell counts in less than 15 minutes. Standard microfabrication techniques have been used to create a microfludic biochip, which uses electrical impedance sensing to analyze small sample volumes (~10 µL) of blood. The biochip progressively gains more functionality during the study. First, a chip was designed to confirm that the electrical impedance pulse counting technique was a viable method to enumerate CD4+ T cells. Three-dimensional hydrodynamic focusing was used to take advantage of the laminar flow regime found in microfludics and increase the counting accuracy of the device. Second, a differential counting stage was added that selectively counted CD4+ T cells from leukocyte (i.e., white blood cell) populations using immunoaffinity chromatography methods. Total leukocyte counts were obtained before and after the cells flowed through a CD4+ T cell depletion chamber. The difference between these two counts proved to be an accurate representation of the number of captured cells when verified with an optical control. Third, an erythrocyte (i.e., red blood cell) lysis module was added, with which to perform accurate counts on unprocessed blood samples, verified with flow cytometry controls. The success of this final stage suggests that the technology described is a viable answer to bringing PoC CD4+ T cell counts into resource-poor regions. An advantage of this label-free technology is that it can be readily expanded to diagnose other diseases and conditions simply by altering the specificity of its depletion chambers to other cell types. Although this dissertation focuses on the specific application of PoC AIDS diagnostics, it also addresses the fundamentals in microfluidic cytometry. The impedance responses of cells under various conditions were studied, including living cells, dead/dying cells, and cells undergoing chemical modification. Leukocyte subsets were distinguished based on their electrical properties found using multiple AC interrogation frequencies, confirming state-of-the-art findings in the literature. This multiple frequency technique gave a better understanding of the morphological and electrical characteristics of leukocytes, such as cell volume and membrane capacitance. Different electrical sensor designs were investigated to increase sensitivity and signal integrity, and to know cell flow direction through the counter. Various sensing channel designs were explored to determine the optimal balance between counting accuracy and fabrication complexity.

Graduation Semester

2012-05

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http://hdl.handle.net/2142/32048

Copyright and License Information

Copyright Nicholas Noel Watkins

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