Date on Master's Thesis/Doctoral Dissertation

5-2012

Document Type

Master's Thesis

Degree Name

M. Eng.

Department

Mechanical Engineering

Committee Chair

Williams, Stuart J., 1981-

Author's Keywords

Dielectrophoresis; Nano-probe; Electrokinetic; Non-uniform electric field

Subject

Dielectrophoresis; Nanoparticles

Abstract

Dielectrophoresis (DEP) is an electrokinetic force capable of attracting or repelling neutrally charged particles due to a non-uniform electric field [1, 2]. Positive dielectrophoresis attracts particles in the region of the highest electric field gradient; negative dielectrophoresis repels particles from the region of the highest electric field gradient. The dielectrophoretic force is directly proportional to the square of the electric field gradient, as well as the cube of the radius of the particles involved. As particles decrease in size, the gradient of the electric field must increase rapidly in order to capture or repel the particles. The intense electric field gradients were produced using fabricated silver gallium (Ag2Ga) nano-probes electrodes in conjunction with indium tin oxide (ITO) coated microscope cover slips, which served as the opposite electrode. The silver gallium nano-probes ranged from approximately 100-500 nm in diameter and were typically positioned less than 40 ?m above the ITO cover slips. Positive and negative dielectrophoretic forces were able to dominate the other electrokinetic forces acting on sub-micron particles, which were suspended in deionized water and aqueous potassium chloride, using the nano-probes and ITO cover slips as electrodes. Colloidal quantum dots of gold, as small as 5 nm in diameter, were captured using positive DEP forces, as were sub-micron fluorescent polystyrene particles. Negative DEP forces repelled sub-micron fluorescent polystyrene particles suspended in a low conductivity solution.

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