1. Dielectrophoretic particle trap: Novel trapping and analysis technique
at single particle level
Tae Joon Kwak, Jörg C. Woehl, Woo-Jin Chang
Department of Mechanical Engineering, Chemistry and Biochemistry, and School of Freshwater Sciences,
University of Wisconsin-Milwaukee

2. INTRODUCTION
• Separation and characterization of bioparticle and cell is important for a wide range of biomedical applications such as pharmaceutical or cancer cell researches.
• Bioparticles must be isolated from their mixture (e.g. blood, serum) before the relevant components are analyzed.
• Recent progress in micro- and nano-technology enables the development of various methods and devices to manipulate molecules such as electrophoresis, dielectrophoresis (DEP), etc.
• Since their small size and low density, however, separation of the bioparticles from other components requires a lot of effort and time.
• Most of the current procedures for bioparticle separation require several processing steps (e.g. centrifugation, filtration) from hours to overnight. Moreover, many of these processes can damage bioparticles.

3. • Thus, a major issue is to develop a method that
reduces the number of processing steps and time for sample collection and bioparticle isolation;
reduces mechanical damage to the bioparticles;
maintains the viability of the bioparticles for identification and analysis.
• In this research, we have applied AC-based dielectrophoresis(DEP) to capture and separate vast number of particles and cells in single particle level.
• The electrical properties of the particles can be determined by combining single particle manipulation and further analytical techniques.
• All traps in the array supply the identical electric field distribution to provide the same operating condition on any particles in the sample solution.

4. MATERIALS AND METHODS Dielectrophoresis (DEP)
• A dielectric particle placed in an electric field becomes electrically polarized as a result of partial charge separation
• The charge separation leads to an induced dipole moment. In a non-uniform electric field, the particle experience dielectrophoretic force.
r – radius of particle
E – electric field
– permittivity of medium
Re[K] – Clasius-Mossotti Factor where
σ = conductivity of electric field
ω = angular frequency of electric field

5. Dielectrophoresis (DEP)
• The direction of the force is determined by the K, as known as the Clausius-Mossoti factor.
• If a suspended particle has higher polarizability than the medium, the DEP force will push the particle toward regions of higher electric field (positive DEP).
• On the other hand, if the medium has a higher polarizability than the suspended particle, the particle is driven toward regions of low field strength (negative DEP).

6. Numerical Simulation
• The trap geometry is designed using numerical simulation to trap single particles. Circular shaped traps are designed for the generation of omni-directional negative dielectrophoretic forces.
• Numerical analysis is also used to calculate the dielectrophoretic force acting on each particle by the voltage applied to the electrode.

7. Lab-on-a-chip Microfluidic System.
• The Lab-on-a-chip microfluidic device was fabricated through micro photolithography process.

8. RESULT AND DISSCUSSION
• The polystyrene particles in the solution flowing in the microchannel moved freely along the flow. Individual particle was trapped in each trap by the trapping force of the DEP force with the aid of the electric field formed around the trap.
• In a trap array, the electric field distribution around each dielectrophoretic trap capturing a particle does not vary from trap to trap. Particles with the same physical and electrical properties are captured in all traps under certain, well-defined conditions.

9. CONCLUSION
• This study will advance the rapid isolation and identification of the molecules and micro- and nano-particles, such as cells, bacteria and DNA in single molecule level, by simultaneous manipulation of large number of the particles under identical condition.