Date of Award


Document Type

Open Access Dissertation


Mechanical Engineering

First Advisor

Guiren Wang


Electrokinetics involves the study of liquid or particle motion under the action of an electric field; it includes electroosmosis, electrophoresis, dielectrophoresis, and electrowetting, etc. The applications of electrokinetics in the development of microfluidic devices have been widely attractive in the past decade. Electrokinetic devices generally require no external mechanical moving parts and can be made portable by replacing the power supply by small battery. Therefore, electrokinetic based microfluidic systems can serve as a viable tool in creating a lab-on-a-chip (LOC) for use in biological and chemical assays. Here we present our works of electrokenitic based mixing and separation in microfluidics systems.

Firstly, we present a novel fast micromixer of quasi T-channel with electrically conductive sidewalls and some newly observed phenomena on mixing process. The sidewalls of the microchannel can be either parallel or non-parallel with an angle. The mixing behaviors in the micromixer with different angles between the two electrodes located at the sidewalls are studied in terms of velocity and scalar concentration distributions. It is found that mixing can be enhanced rapidly at a small angle about 5° between the two electrode sidewalls even at low AC voltage, compared with that in parallel sidewalls. The effectiveness of several parameters were explored for the further enhancement of the fluid mixing, including conductivity gradient, AC electric flied frequency, applied voltage, AC signal phase shift between the electrodes, etc. The results reveal that the mixing is the stronger under high conductivity gradient, low frequency, high voltage and 180º signal phase shift between the two electrodes. Fast mixing under high AC frequency can be achieved in this quasi T-channel micromixer as well. The most important observation is that for the first time turbulence can be achieved under AC electrokinetic forcing at low Reynolds number in the order of 1 in this novel design. Thus, turbulent mixing can also be generated in micofluidics to cause rapid mixing. The turbulent flow is also measured with laser induced fluorescence photobleaching anemometer.

Secondly, we have successfully manipulated and isolated cancer cells from other cells and bio-particles, by dielectrophoresis (DEP) in a microfluidic platform in a continuous operation. In this cell sorter, the cancer cells were treated as target cells and were deflected to a side channel from a main channel as they experienced a negative DEP force, when an AC electric field at the cross-over frequency of the cancer cells was supplied. This motion consequently led to the separation of the cancer cells from other cells and bio-particles. Colorectal cancer cells (HCT116) were firstly separated from human Embryonic Kidney 293 cells (HEK 293) and Escherichia coli (E. coli) bacterium. Then prostate cancer cells (LNCaP) were separated from HCT116 cells. Furthermore, we developed a cascade configuration sorter to increase purity of the isolated target cells, and a staggered sorter with two side channels in opposite side walls to increase sample throughput without compromising enrichment factor. Comparing to a single side channel DEP cell sorter, the isolation purity was improved from 80% to 96% by single cascade sorter and the sample throughput was increased from 0.2 µL/min to 0.65 µL/min by a single staggered side channel sorter.

Here we report the theory and method, experimental setup, results and discussion. The future work and direction will be proposed as well.