Lin Yung-Yi, Lo Ying-Jie, Lei U
Nanometrics Incorporated, Milpitas, CA 95035, USA.
Institute of Applied Mechanics, National Taiwan University, Taipei 10617, Taiwan.
Micromachines (Basel). 2020 Mar 22;11(3):329. doi: 10.3390/mi11030329.
A simple and inexpensive method using planar electrodes was proposed for the measurement of the imaginary part of the Clausius-Mossotti factor, K i , of particle/cell for electrorotation (ER) and travelling wave dielectrophoresis (twDEP). It is based on the balance between the dielectrophoretic and viscous torques on a particle undergoing ER subject to dual frequency operation in an ER chamber. A four-phase ac voltage signal with a given frequency is applied for generating ER for measurement, and another two-phase signal is applied at a selected frequency for generating a negative dielectrophoretic force for confining the particle motion, instead of using laser tweezer or three-dimensional electrodes in the literature. Both frequencies can be applied to the same electrodes in a four-electrode ER system and to alternative different electrodes in an eight-electrode ER system, and both systems are capable for providing accurate measurement. The measurements were validated by comparing with the theoretical result using sephadex particles in KCl solution, and with the existing experimental results for various human cancer cells in medium with conductivity from 0.01-1.2 S/m, using ER with optical tweezer and dual frequency twDEP. Contrast between the ER and the twDEP methods (the current two available methods) was discussed and commented. The present method could provide measurement for wider frequency range and more accurate result near K i = 0, in comparison with the results using the twDEP method. However, the twDEP method could perform much more rapid measurement. Detailed forces and torque were calculated inside the ER chamber for understanding the physics and assessing the characteristics of the dual frequency ER method. This study is of academic interest as the torque in ER and the force in twDEP can be calculated only when K i is known. It also finds biomedical applications as the K i -spectra can be served as physical phenotypes for different cells, and can be applied for deriving dielectric properties of cells.
提出了一种使用平面电极的简单且低成本的方法，用于测量粒子/细胞的克劳修斯 - 莫索蒂因子的虚部(K_i)，以用于旋转电场（ER）和行波介电泳（twDEP）。它基于在ER腔中经历双频操作的粒子上的介电泳扭矩和粘性扭矩之间的平衡。施加具有给定频率的四相交流电压信号以产生用于测量的ER，并且以选定频率施加另一个两相信号以产生用于限制粒子运动的负介电泳力，而不是像文献中那样使用激光镊子或三维电极。这两个频率都可以应用于四电极ER系统中的同一电极，以及八电极ER系统中的交替不同电极，并且这两个系统都能够提供准确的测量。通过将使用KCl溶液中的葡聚糖颗粒的测量结果与理论结果进行比较，以及将使用ER与光镊和双频twDEP的各种人类癌细胞在电导率为0.01 - 1.2 S/m的培养基中的现有实验结果进行比较，验证了测量结果。讨论并评论了ER方法和twDEP方法（目前两种可用方法）之间的对比。与使用twDEP方法的结果相比，本方法可以在更宽的频率范围内进行测量，并且在(K_i = 0)附近提供更准确的结果。然而，twDEP方法可以进行更快的测量。计算了ER腔内的详细力和扭矩，以理解物理原理并评估双频ER方法的特性。这项研究具有学术意义，因为只有当(K_i)已知时才能计算ER中的扭矩和twDEP中的力。它还发现了生物医学应用，因为(K_i)光谱可以作为不同细胞的物理表型，并可用于推导细胞的介电特性。
