SOUTHERN TAIWAN UNIVERSITY Multi-step dielectrophoresis for separation of particles Student: Bui Tuan Anh ( 裴俊英 ) Professor: Yi – Chu Hsu Class: Nano-MEMS

SOUTHERN TAIWAN UNIVERSITY CONCEPT 1. Introduction 2. Theory of method 3. Experiments and calculations 4. Results and dicussion 5. Conclusion

SOUTHERN TAIWAN UNIVERSITY 1. Introduction Separation of micro particles with different properties is an issue of great importance. One of most common methods is flow cytometry

SOUTHERN TAIWAN UNIVERSITY This paper proposed a separation method based on principle of Dielectrophoresis (DEP). Particles in micro-flow channel will be trapped and released in a number of steps. Each step will improve resolution.

SOUTHERN TAIWAN UNIVERSITY 2. Theory of method 2.1. DEP mobility If the medium is moving with velocity u f, then the total velocity u tot of particles is: u DEP is the velocity of a particle induced by DEP. is the DEP mobility. is the gradient of the squared electrical field.

SOUTHERN TAIWAN UNIVERSITY A spherical particle with radius r, in the medium with viscosity, the DEP mobility is: is the real part of the complex effective polarisability of the particle. is conductivity and is permittivity

SOUTHERN TAIWAN UNIVERSITY 2.2. Multi-step DEP trapping The trap-release step incluse 3 phase: Phase a: Particles are focused in the middle of channel Phase b: Trap Phase c: Release

SOUTHERN TAIWAN UNIVERSITY The particles are trapped and released from electrode. If the difference in mobility bteween the particles to small, using one trap and release step will not be enough to achieve compete separation. Besides that, it’s difficult to trap the particles with only single pair of electrodes.

SOUTHERN TAIWAN UNIVERSITY After several steps the separation is complete. Therefore, an array of interdigitated electrodes will be utilized.

SOUTHERN TAIWAN UNIVERSITY To quantify the level of fractionation in this method, a DEP resolution factor R DEP between two particle populations A and B is define as: d is the distance between the two centers of each particle populations w is the distance between the particles most far apart within each population.(wide of population) Two particle populations are completely separated if R DEP =1.5.

SOUTHERN TAIWAN UNIVERSITY The resolution will continue to increase as a direct function of the number of steps. Hence, the DEP resolution R DEP can be expressed as: Where the C R is a constant value reflecting the separation increase in each step. And N DEP is a number of steps.

SOUTHERN TAIWAN UNIVERSITY 3. Experiments and calculations Experimental conditions: Particles: Polystyrene micro beads Flow channel: micro-flow channel Number of eletrode: 15 electrodes /1 step Velocity of flow is 50. Voltage phase angle between two adjacent electrodes is 180° ( ). Width of one electrode and distance between two adjacent electrode is 0.5 L 0.

SOUTHERN TAIWAN UNIVERSITY To icrease the trapping efficiency, and to extend the separation range, superpositioned AC field are utilized. This means that the arrays of interdigitated electrodes are used both at top and bottom of the channel. Then the velocity of the particles in the trapping phase is calculated: where u pDEP,u nDEP are the velocity induced by positive DEP and negative DEP, respectively.

SOUTHERN TAIWAN UNIVERSITY In the release phase, both arrays of electrodes push the particles to the middle of the channel, then velocity become: In this research, the radius of polystyrene beads is set to 0.05 L 0. Then, the maximum DEP mobility of polystyrene particle is 1.2x m 4 /V 2 s at low frequencies(<5kHz).

SOUTHERN TAIWAN UNIVERSITY At low frequency (<5kHz), the positive DEP motion will be increased. And at high frequency it could be reduced. For negative DEP, a suitable frequency would be 5MHz.

SOUTHERN TAIWAN UNIVERSITY 4. Results and discussion A difference in size will have largest influence on DEP mobility Separate particles with a 5% size difference, only 2 step are used to obtain a complete separation (R DEP >1.5). For 2% size difference, we need 4 step, while 8 would be required to separate particles with 1% difference in size.

SOUTHERN TAIWAN UNIVERSITY When size difference is 0.2%, number of steps we need is about 200 steps.

SOUTHERN TAIWAN UNIVERSITY Differences in Conductivity have a lower impact on DEP mobility than differences in size. If differences in conductivity is reduced to 18%, no separation at all is achiveved in the first trapping phase, and then any separation would be impossible.

SOUTHERN TAIWAN UNIVERSITY Also with a differences in permittivity of 62%, it is a limitation of separation.

SOUTHERN TAIWAN UNIVERSITY 5. Conclusions -The separation method based on repetitive DEP trapping and release in a flow system. -The resolution R DEP is a funtion of the number of steps. -Calculations for some model particles showed that it should be to obtain a complete separation for a 0.2% size difference after about 200 steps. -The limiting value of diffrences in conductivity is 18% that separations can not performed.

SOUTHERN TAIWAN UNIVERSITY The power of multi-step DEP could be of great interest, not only for fractionation of particles, but also for measuring changes in surface conductivity.

SOUTHERN TAIWAN UNIVERSITY Thanks for your attention.