Date of Award

Spring 1-1-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Advisor

Victor M. Bright

Second Advisor

John Moreland

Third Advisor

Y. C. Lee

Abstract

This work describes a new magnetic manipulation technique to trap, release, transport, and detect superparamagnetic beads (SPBs) with low-power and addressable spin-valves (SVs). Functionalized SPBs are used as "mobile substrates" or magnetic tags in numerous bioassays. Examples of applicable bioassays include protein and DNA purification, cell fractionation, enzyme immobilization, and immunoassays. SV technology is based on the giant magnetoresistance (GMR) effect and is commonly used in high-density magnetic recording heads and magnetic field sensors. The SV consist of two magnetic layers separated by a spacer layer. An antiferromagnetic (AFM) layer pins the magnetization of one ferromagnetic (FM) layer in one direction while the other FM layer remains free to rotate. When the two layers are parallel (low resistance state), the high magnetic field gradient will attract and trap a SPB. When the two layers are antiparallel (high resistance state), the gradient is low and the SPB will no longer be attracted to the SV; the SPB will be released. In addition to SPB capture and release, the stray fields from a trapped and magnetized SPB affect the SV resistance response, thus a trapped SPB can be detected. The scope of this thesis includes the design, fabrication, and characterization of the microfluidic and micro-electromechanical system (MEMS) to manipulate and detect SPBs with nonvolatile and locally addressable SVs.

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