使用介電泳分離微粒子之計算探討

Abstract

本研究主要利用介電泳原理在微流體裝置下以分離同性質之不同大小群體微粒子，並計算分析此一分離過程。此一過程是藉著設計不同電極的形狀，包括有層狀電極、梯狀電極、雷狀電極三種形狀，以產生異質非均勻電場的效應。在本研究中，通過電場的粒子大小選定為5微米、10微米、15微米和20微米，並藉由負介電泳作用力(粒子遠離電場較強的方向)和史托克力(流體的阻力)的相互作用，使得粒子通過電場。這種負介電泳作用力是由Clausius-Mossotti (CM) 因子的參數對應頻率範圍所選定。因此，分離的結果是經由負介電泳作用力和史托克力(流體的阻力)的總和所推導出的粒子軌跡方程式而計算出的。並分析分離因子(負介電泳作用力和史托克力的比值)與分離結果的關係，來探討粒子作用力的平衡和在三種不同形狀電極下的分離狀態。 經由本研究的計算，當頻率大於600赫茲時，不同大小的粒子可於層狀電極和梯狀電極中依據其尺寸被分離。整體而言，本研究所採用的分離因子與分離的效果有極為密切的關係。根據分離因子的分析，發現當電極的交流輸入訊號增加時，可分離粒子之流速也會隨之增加且流速範圍加大，這是本研究極為重要的考量之一。而在雷狀電極的設計及計算結果的分析中，當粒子大小同時包括有10微米、15微米、20微米時，其分離結果良好。且當粒子大小同時有5微米和10微米時亦然。然而，當粒子大小同時包括有5微米、10微米、15微米和20微米時，則其分離的結果不佳。

This thesis presents the computation of separation of size-specific particles using dielectrophoresis (DEP) in a microfluidic device. The goal of the study is to separate heterogeneous population of particles into bins downstream. Different configurations of electrodes are designed, such as gradual, step, and deterministic, in order to achieve non-uniform electric field strength. Particles of diameters 5μm, 10μm, 15μm, and 20μm are used. Parameters of the Clausius-Mossotti (CM) factor were determined to achieve negative dielectrophoresis (nDEP) at the range of specified frequencies. The relations between negative dielectrophoretic force (nDEP) and drag force are used to derive the governing equation of particle trajectories. An overarching parameter, called sorting factor, was derived to account for the force balance on the particle and it also serves to compare performance among the three electrode designs. Results of computation showed that size-specific particles could be separated at the frequency above 600Hz by using gradual and step electrode designs. As a whole, the sorting factor serves well to correlate the efficacy of separation in most cases studies. According to sorting factor analysis, if the input A.C. signals increases, the range of the flow velocity also increases which is an important consideration for this device. Furthermore, the suitable input A.C. signals are chosen for this experiment. However, the deterministic electrodes of these devices may separate particles of 10μm, 15μm, and 20μm in diameters and particles of 5μm and 10μm in diameters. For the moment of the result of computation, the deterministic electrode of this device may not completely separate size-specific bioparticles.