| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 106 === Dielectrophoresis (DEP) has been extensively used in lab-on-a-chip systems for trapping, separating and manipulating micro-substance suspended in liquid medium.
Base on the frequency of electric field, the DEP force can be classified into two types, the positive DEP force and negative DEP force, which means the direction of force will be toward or away from the high gradient region of electric field. In our work, we apply optical tweezer (OT) system as a precise force detector to capture the micro-particle, exert frequency sweep of AC electric field, and then get the positon or force signal by quadrant photodiode (QPD) in OT system. After processing signal, we can measure the frequency-dependent dielectrophoretic properties.
Since electro-hydrodynamic (EHD) effect, such as electro-osmosis and electric thermal flow, will influence the measured result, to discuss and quantify the EHD effect, we will capture the particle in different positions to do measurement, and utilize finite element simulation to calculate flow field of EHD effect. In the other hand, functional group on the particle surface will change its overall dielectric properties, and cause variation of crossover frequency. To explain its mechanism, we do simulation curve fitting to fit experiment data, and then analyze the result.
By coming experiment measurement and simulation analysis, we analyze what factors will affect the value of crossover frequency of polystyrene micro-particle, and quantify both the EHD and DEP effect to micro-particle. And by our work, we also provide the most proper method to measure the pure DEP phenomenon.
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