Date of Graduation

12-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Microelectronics-Photonics (PhD)

Degree Level

Graduate

Department

Graduate School

Advisor

Ingrid Fritsch

Committee Member

Chao-Hung S. Tung

Second Committee Member

Christa Hestekin

Third Committee Member

David Paul

Fourth Committee Member

Kenneth G. Vickers

Keywords

Pure sciences; applied sciences; Biosensing; Electrochemistry; Lab-on-a-chip; Microfabrication; Microfluidics; Redox-magnettohydrodynamics

Abstract

Unique microfluidic control actuated by simply turning off and on microfabricated electrodes in a small-volume system was investigated for lab-on-a-chip applications. This was accomplished using a relatively new pumping technique of redox-magnetohydrodynamics (MHD), which as shown in this dissertation generated the important microfluidic features of flat flow profile and fluid circulation. MHD is driven by the body force, FB = j × B, which is the magnetic part of the Lorentz force equation, and its direction is given by the right hand rule. The ionic current density, j, was generated in an equimolar solution of potassium ferri/ferro cyanide by applying a constant current/potential across the gap between an anode-cathode pair of the electrodes. The magnetic field, B, was produced with an NdFeB permanent magnet beneath the chip.

Two types of microelectrode geometries were used in this dissertation: microbands and concentric disks and rings. Horizontal flow profiles having uniform velocities (≤124.0 µm/s) at fixed heights across different gaps were sustained along a ~25.0 mm path using microband electrodes, in a small volume contained over an insulated silicon chip. Microfluidic rotational flow with velocity ≤ 14 µm/s was also achieved over an annular region between concentric disk (radius: 80 µm) and ring (inner radius: 800 µm) microelectrodes. In a different but related series of studies, natural convection generated by electrochemical processes was studied in a steady state microfluidic system, but without using redox-MHD convection. Natural convection was found to generate a maximum fluid velocity of < 10 µm/s radially across the gap between concentric disk-ring microelectrodes.

A proof-of-concept magnetic microbead enzyme assay was also integrated with the redox-MHD flat flow profile generated by [Ru(NH3)6]3+/2+ in Tris buffer. Selective placement of the assay complex at different locations combined with the uniform transport of the electroactive species by-product generated a strong current signal at the locations that were on the same flow path as the detector. When the assay complex was placed at other locations that were on parallel flow paths the current signal at the detector was insignificant (20%), thus confirming the potential of redox-MHD microfluidics to perform multiple, parallel assay detections.

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