Electrokinetic Micromixer and Cell Manipulation Platform Integrated with Optical Tweezer for Bio-analytical Applications

by Chien, Yu-sheng

Abstract (Summary)
Integrated microfluidic devices for biomedical analysis attract lots of interest in the MEMS (Micro-Electro-Mechanical-Systems) research field. However, the characteristic Reynolds number for liquids flowing in these microchannels is very small (typically less than 10). At such low Reynolds numbers, turbulent mixing does not occur and homogenization of the solutions occurs through diffusion processes alone. Hence, a satisfactory mixing performance generally requires the use of extended flow channels and takes longer to accomplish such that the practical benefits of such devices are somewhat limited. Consequently, accomplishing the goal of u¡VTAS requires the development of enhanced mixing techniques for microfluidic structures. This study first presents a microfluidic mixer utilizing alternatively switching electroosmotic flow and proposes two microchannel designs of T-form and double-T-form micromixer. Switching DC field is used to generate the electroosmotic force to drive the fluid and also used for mixing of the fluids simultaneously, such that moving parts in the microfluidic device and delicate external control system are not required for the mixing purpose. Furthermore, this study also proposed a novel pinched-switching mode in the T-form microfluidic mixer, which could be effectively increase the perturbation within the fluid to promote the mixing efficiency. In this study, computer simulation for the operation conditions is used to predict the mixing outcomes and the mixing performance is also confirmed experimentally. Result shows the mixing performance can be as larger as 95% within the mixing distance of 1 mm downstream the common boundary between the different sample fluids. The novel method proposed in this study can be used for solving the mixing problem in a simple way in the field of micro-total-analysis-systems. Furthermore, in order to demonstrate the proposed micromixer is feasible for on-line bio-reaction, this study designs a fully integrated device for demonstration of DNA/enzyme reaction within the microfluidic chip. The microchip device contains a pre-column concentrating region, a micro mixer for DNA-enzyme mixing, an adjustable temperature control system and a post-column concentration channel. The integrated microfluidic chip has been used to implement the DNA digestion and extraction. Successfully digestion of £f-DNA using EcoRI restriction enzyme in the proposed device is demonstrated utilizing large-scale gel electrophoresis scheme. Results show that the reaction speed doubled while using the microfluidic system. In addition, on-line DNA digestion and capillary electrophoresis detection is also successfully demonstrated using a standard DNA-enzyme system of $X-174 and Hae III. Finally, this reasearch also proposes a novel cell/microparticle manipulation platform by integrating an optical tweezer system and a micro flow cytometer. During operation, electrokinetically driven sheath flows are utilized to focus microparticles to flow in the center of the sample stream then pass through an optical manipulation area. An IR diode laser is focused to generate force gradient in the optical manipulation area to manipulate the microparticles in the microfluidic device. Moving the particles at a static condition is demonstrated to confirm the feasibility of the home-built optical tweezer. The trapping force of the optical tweezer is measured using a novel method of Stocks-drag equilibrium. The proposed system can continuously catch moving microparticles in the flowing stream or switch them to flow into another sample flow within the microchannel. Target particles can be separated from the sample particles with this high efficient approach. More importantly, the system demonstrates a continuously manipulation of microparticles using non-contact force gradient such that moving parts and delicate fabrication processes can be excluded. The proposed system is feasible of high-throughput catching, moving, manipulation and sorting specific microparticles/cells within a mixed sample and results in a simple solution for cell/microparticle manipulation in the field of micro-total-analysis-systems. In this thesis, low-cost soda-lime glass substrates are adopted for the microchip fabrication using a simple and reliable fabrication process. Three kinds of novel microfluidic devices including an electrokinetically-driven microfluidic mixer, a high throughput DNA/enzyme reactor and an optically cell manipulation platform are successfully demonstrated. It is the author¡¦s believes that the results of this study will give important contributions in the development of micro-total-analysis-systems in the future. With the success of this study, we have a further step approaching to the dream of lab-on-a-chip system for bio-analytical applications.
Bibliographical Information:

Advisor:Che-hsin Lin; Fu-jen Kao; Chii-rong Yang; Lung-ming Fu

School:National Sun Yat-Sen University

School Location:China - Taiwan

Source Type:Master's Thesis

Keywords:biomedical analysis microfluidic optical tweezer electroosmotic flow micromixer cell manipulation


Date of Publication:07/20/2005

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