Development of an Active Micromixer by Dielectrophrosis Particle Manipulating 姓名：黃朝鴻 Chao-hong Huang 班級：奈米一甲 學號：ＭＡ１１Ｖ１０８

Abstract A particle manipulating micromixer was developed successfully in this study. The present device was fabricated by simply MEMS process. Only two photomasks, one for electrode array chip and another for micro- channel, were needed to manufacture the micromixer. Dielectrophoresis (DEP) force was used to manipulate the particles in the micro-channel. In this experience, polymer particles with diameter of 1­m were tested in the fluid with conductivity of 0.10mS/cm. The results show that the symmetrical vortices were observed at frequency of 100 kHz. The traveling wave DEP (twDEP) occurred when the input frequency was 10MHz. The flow phenomena were obtained and analyzed by micro-PIV technology. In the future, different cells can be manipulated by the present micromixer to achieve the rapid mixing with different driving frequency. It is useful in the biological or biomedical application.

Introduction Introduction In 1950, H.A. Pohl has put forward a brand-new theory, called dielectrophoresis (DEP), to the movement in the even electric field of particle. DEP, in general, has been explored for particle characterization, manipulation, and separation. DEP, however, can be further specified with “conventional DEP (cDEP), “rotation DEP (rotDEP)”, “traveling DEP (twDEP). RotDEP and cDEP are believed to be more suitable for cell characterization and separation while twDEP offers distinct advantages for cell manipulation in terms of motion control, cell selectivity, and the minimization of cell-cell interferences In addition to the handling of cells, beads, bacteria, viruses, and molecules, twDEP can also be applied to separate mixtures of different bio-particles.

Working principle The parallel microelectrodes were used to manipulate the polymer particles and cause the vortex which can stir fluid to achieve mixing. To verify the mechanism of mixing phenomena, the micro-PIV technology was used to demonstrate the flow flied when the microelectrodes triggered.

Chip fabrication and experimental setup A glass slide with a thickness of 1 mm was used in the production of microchip. The thin film with 300 Å Chromium and 1700 Å gold was evaporated by an E-beam evaporator. The wet-etching process was applied after the patterns were exposed and developed. Particle manipulate zone used 10 parallel golden electrodes with same interval which can provide 90˚phase shift between each electrode.

Results In the experiment, two flow conditions for the present micromixer were carried out. One for stationary fluids and one for two-fluids moving flow. For the first testing condition, the fluorescent polymer particles with diameter of 1­m were used in a fluid with conductivity of 0.10mS/cm. A pair of vortices can be observed in the region of the electrode array at input frequency of 100KHz.

Direction of the particles When particles in the fluid with conductivity of 0.10mS/cm, the twDEP effect in the tip of electrodes is obvious at frequency of 10 MHz. We can adjust the phase arrangement to control the moving direction of particles.

Mixing process The flow visualization by the blue dyes and DI water with particles was utilized to observe the mixing process in a time sequence.

Mixing ratio The manipulated particles stirred the two fluids and the interface was stretched. The ink moved toward the lower region as time increased. The experimental results revealed that the mixing occurred at the confluence between two vortices which induced by the particles. The mixing rate was thus obtained by calculating the ratio of the ink area, A, at different time and the initial ink area, A 0, as given in Fig. 8. The results indicate that the mixing was mainly due to diffusion when the driving voltage was lower than 10V.

CONCLUSIONS A new application of DEP in flow mixing has been developed in this study. The DEP micromixer was shown to be able to mix two fluids efficiently by manipulating micro particles with DEP forces especially for very low Reynolds numbers. Moreover, the micro-PIV measurement can provide detailed flow information, which is useful to optimize the design of the micromixer. In the future, different cells can be manipulated by such a DEP micromixer chip to mix with drugs.

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