光鉗輔助量測並量化電液動流對微粒子在不同溶液導電度及抓取位置下之介電泳交越頻率影響

Using optical tweezer system to measure and quantify AC electro-hydrodynamic effect to frequency-dependent dielectrophoretic phenomenon of micro-particle varies with different medium conductivities and captured positions

呂昀緯(Yun-Wei Lu)

指導教授 ： 莊嘉揚

國立臺灣大學/工學院/機械工程學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201802480

摘要

在實驗室晶片研究中微粒子操控是非常普遍且重要的應用，介電泳現象因此被大量運用在實驗室晶片上，藉由改變外加交流電場之頻率與電極之幾何形狀設計，使介電粒子受到特定方向介電泳力，進而進行微粒子的分離、捕捉與操控。介電泳性質的基礎量測與資料對於其應用上有很大的幫助。
由於介電泳力對於頻率之響應分為正-介電泳與負-介電泳，即介電泳力方向可能為指向或遠離電場梯度最強方向，在接近正負介電泳力反轉時頻率，稱作交越頻率。本研究利用光鉗作為量測微粒子受力之精準力感測器，捕捉液體中微粒子至聚焦雷射光腰中心位置，操控微粒子至電極間特定位置並輸入不同頻率之交流電場，介電泳力使粒子偏移雷射中心，粒子受力和粒子與雷射中心距離成正比，而粒子偏移量之大小可以由光電四象儀測得，因此藉由此系統能夠讀取微粒子受力後之偏移情形與震動訊號，進行訊號處理後即可測得交越頻率。
電液動現象如電滲、電泳在電極附近會產生明顯的流場作用，對微粒子交越頻率的量測會產生一定程度的影響，為了探討電液動現象對介電泳交越頻率量測的影響，本研究將微粒子擺在不同位置相對於電極進行實驗量測，透過光鉗系統量測微粒子受介電泳力之大小，搭配有限元素模擬分析建立一電液動流場模型量化微粒子受流場之黏滯力影響。除此之外，微粒子的表面修飾官能基同樣會很大程度地影響交越頻率大小，這部分同樣會由實驗量測不同官能基之微粒子與有限元素模擬進行數值擬合進行分析及探討。
由上述實驗及模擬結果，我們量化了量測微粒子介電泳現象時受電液動流場的影響，解釋為何在特定條件下會量測到相對偏低的實驗結果，並探討表面官能基對交越頻率之影響，最後提供如何量測介電泳現象的最佳方式。

關鍵字

介電泳 ； 交越頻率 ； 馬克斯威應力張量 ； 光鉗 ； 電滲流 ； 電熱流 ； 電液動流 ； 表面官能基

並列摘要

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.

並列關鍵字

Dielectrophoresis ； crossover frequency ； Maxwell stress tensor ； Optical tweezer system ； electro osmosis ； electric thermal effect ； surface functional group

參考文獻

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