September 2, 2008

Soumya K Srivastava


Soumya K Srivastava - “Continuous Electrodeless Dielectrophoretic Separation in a Circular Channel” L. Zhang, F. Tatar, P. Turmezei, J. Bastemeijer, J.R. Mollinger, O. Piciu and A. Bossche Journal of Physics: Conference Series
 
Presented by Soumya Srivastava Journal Club fall’08- 09/02/08 “Continuous Electrodeless Dielectrophoretic Separation in a Circular Channel” L. Zhang, F. Tatar, P. Turmezei, J. Bastemeijer, J.R. Mollinger, O. Piciu and A. Bossche Journal of Physics: Conference Series Summary: Many separation techniques have been developed with respect to particle charge, size, density and specific biological markers. Novel physical methods of separating particles based on the dielectric properties have been explored here. Previous research has involved many dielectrophoretic methods for separation- migration, affinity, field flow fractionation and traveling wave. In all of this AC field is generated by different electrode geometries or arrays, which cause gas generation due to electrolysis. To avoid this problem, electrodeless dielectrophoresis were carried out for separation. Since these methods lacked high throughput continuous separation, a new electrodeless dielectrophoresis method was required for continuous separation. A novel method for continuously separating particles based on electrodeless DEP is demonstrated in this article. This separation is achieved by applying electric field on circular channel. Electro-osmotic flow aids the particles to move continuously across the channel. Separations into different outlets occur when the particles with different dielectric properties move to different locations across the channel due to different dielectrophoretic force. Here, authors have modeled and simulated the separation of particles using finite element analysis and have shown that particles of different dielectric properties can be separated spatially and in time domain. The advantage of using this structure is that, it can be easily fabricated, is mechanically robust and chemically inert and can yield high throughput and continuous separation. Basic principle of this circular channel design involves generating non-uniform electric field by applying DC voltage on two electrodes. The gradient of electric field is directed towards the center. Particles move in the channel by electro-osmotic force and get separated into different outlets due to different dielectrophoretic force magnitudes and directions. Particle movement depends on Claussius-Mossotti factor and particle size, so particles with positive DEP response move away from the center, whereas particles with negative DEP responses move towards the center. Position of particles with positive response is inner to the inlet whereas particles with negative responses are outer to the inlet channel. Particles whose DEP responses are similar, then the position depend on size of particles- larger particles have higher mobility and fast movement towards inner or outer ends of channels. This circular channel can therefore be used to separate particles of different DEP polarities and same DEP polarities but different sizes. Also, particles choosing inner path move faster than particles on the outer path, since the flow velocity directly depends on electric field intensity. To simulate and model particle behaviors, MATLAB and FEMLAB were used. Dimension of inner channel was 50 micron; outer channel was 100 micron with 20 micron channel height; 10V was applied over the circular channel with zeta potential chosen to be 0.1V and water as suspending medium. Field density was at its maximum at the center of the circular channel. Trajectories of four different particles were simulated- 5 and 10 micron radii for both positive and negative DEP particles. Claussius-Mossotti factor was chosen to be 0.5 for positive DEP and -0.5 for negative DEP. 10 micron positive DEP particle were closest to the center whereas 10 micron negative DEP particles were the farthest from the center. Varying voltages resulted in change of particle trajectories. It is important to choose proper voltage for good separations to be achieved. Left figure shows not good separations at lower voltages and right one shows overly separated particles at higher voltages. 1. Research Technique a. Circular channel electrodeless DEP b. Looks like an adaptable design to our lab c. Variables- Field strength and size of particles 2. Theory a. Starts with dielectrophoretic force equation for a spherical particle b. Also indicates dielectrophoretic mobility for spherical particle c. Ignored Brownian motion and buoyancy force at low Reynolds number for small particles 3. Results a. Flow velocity proportional to electric field intensity b. Positive DEP particle were closest to the center whereas negative DEP particles were the farthest from the center c. Varying voltages resulted in change of particle trajectories i. No specific numbers on voltages 4. Conclusions a. They have to experiment with biological samples to study the separation b. They have to fabricate the design 5. Overall a. Novel technique of using circular channel at M.D.-ERL b. Short paper and well communicated c. Lacks depth and experimentation results d. Figures are not very well represented- lack of labels on the trajectories as to which represents what e. English usage not well- e.g. radiuses
 
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