Microfluidic Continuous Separation of Particles and Cells by using AC-Dielectrophoresis

Abstract

AC-dielelectrophoresis is utilized inside a lab-on-a-chip device to separate particles and cells. Dielectrophoresis is the movement of particles in a non-uniform electric field due to the interaction of the particle's dipole and spatial gradient of the electric field. Dielectrophoresis is a subtle solution to manipulate particles and cells at microscale due to its favorable scaling for reduced size of the system. Dielectrophoresis is applicable with both DC and AC fields. DC-dielectrophoresis only depends on the electrical conductivities of the particle and the medium. AC-dielectrohoresis depends on the permittivities of the particle and the medium, and the field frequency. AC-dielectrophoresis is richer in the sense that both positive and negative dielectrophoretic force can be generated for biological particles by tuning the field frequency. The dielectrophoretic force depends on the size and the electrical properties of the particles and the suspending medium which makes the separation of particles and cells based on their size and based on their electrical properties possible. In this dissertation, the continuous separation of particles and cells based on their size and based on their electrical properties is achieved inside a lab-on-a-chip device. PDMS (polydimethylsiloxane) microchannels are fabricated using soft lithography technique. The flow is induced by pressure gradient. Simple, 3D electrodes which are fabricated by a simple and inexpensive technique extended from soft-lithographic fabrication are used to achieve a localized, non-uniform electric field. Dielectrophoretic force is generated in the transverse direction to the flow by inserting 3D electrodes along the channel side walls. The localized electric field is important to reduce the Joule heating and any adverse effects on biological particles due to the interaction of particles with the electric field. Latex particles of different size and mixture of white blood cells (which have a typical size of 8-12 micron) and yeast cells (which have a typical size of 3-5 micron) is separated based on their size difference. The separation based on electrical properties is demonstrated by means of the separation of 10 micron latex particles and white blood cells. A numerical simulation based on Lagrangian tracking method is used to simulate the particle trajectories. The present designs have the feature of using simple electrodes like DC-dielectrohoretic devices and of using low electrical potential like AC-dielectrophoretic devices; they are unique in a sense that the effect of the electric field is confined in a small area which means a very short time for the interaction of the particles with the electric field.