Generalized Dielectrophoresis near Walls – Theory, Experiment and Application
Date Issued
2010
Date
2010
Author(s)
Lo, Ying-Jie
Abstract
Generalized dielectrophoresis (DEP), including conventional DEP, electrorotation, and travelling wave DEP, are effective tools in the manipulation and characterization of particles in micro-fluidic systems. Current theory in literatures was derived for a particle in an infinite medium. However, most of the particle manipulations are performed in a confined region. Effect of wall(s) could be important. The goal of this dissertation is to carry out a rigorous study on generalized DEP in the vicinity of wall(s), and apply it to perform characterization and manipulation of various cells.
Quasi-static force and torque expressions were derived on a spherical particle next to a wall and between two parallel walls using effective moment approach and image method. According to the theory, the wall effect is minor for electrorotation, traveling wave DEP, and conventional DEP parallel to wall(s), but could be significant for conventional DEP perpendicular to the wall. Such theoretical findings were numerically validated using the Maxwell stress tensor calculation in a purely radial electrical field, and experimentally through suitable force balances between DEP force, viscous fluid drag and buoyancy in an approximate radial field and an approximate uniform field. The experiments with polystyrene particles in de-ionized water agree with the theory within 8.1% discrepancy. The repelling normal DEP force associated with the (insulated) wall effect was found to be a powerful mechanism to focus particles to flow along particular path parallel to the wall(s) in micro channels, and employed to construct the devices in the present study.
Two radial flat micro channels based on suitable force balances were designed and fabricated for the measurements of the real and imaginary parts of the Clausius-Mossotti factors for various cells. The Clausius-Mossotti factors are distinct for different cells, and can probably be served as distinct phenotypes for cancer cells of similar origin but at different metastatic stages. A microfluidic device was thus designed and fabricated for cell manipulation. It consists of a rectangular flat channel with grooves (or holes for capturing single cells) on its ceiling and two large electrodes on the bottom wall at both ends. Under proper geometry and operation, we can design various net forces acting on the particle at different elevations of the device, and thus perform particle isolation and separation. 100% isolation of various cells can be obtained essentially provided that the operation flow rate is sufficiently small (say, less than 20 ul/h). For the separation, preliminary result for lung cancer cells shows that 68% of CL1-0 and 33% of CL1-5 (more invasive) can be captured in the grooves at 5 MHz and 40ul/h. The result may be improved by repeating the operation in sequence.
A possible CTC detection (detecting rare cells in blood) device is proposed based on continuous lysis of red blood cells as the medium flows through the device with the rare cells survive. The device is essentially a micro channel with an electrode array on its bottom wall, with ac voltage applied at neighboring electrodes. As the medium flows through the device, the cells are subjected to the polarized force associated with the electric field, the fluid shear, and the thermal effect due to Joule heating. It is found that the red blood cells are continuously lyzed as the medium flows through the device, with the cancer cells (here is CL1-5) left at the exit because of their stronger mechanical properties.
Subjects
generalized dielectrophoresis
wall effects
Clausius-Mossotti factor measurements
cell isolation and separation
cell lysis
CTC detection
SDGs
Type
thesis
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