| Summary: | 碩士 === 國立成功大學 === 醫學工程研究所碩博士班 === 92 === Dielectrophoretic forces are the forces created on a polarizable particles (e.g. a biological cell) when exposed to non-uniform electric field. A particle can be translated towards the regions of high field intensity (positive dielectrophoresis) or low field intensity (negative dielectrophoresis) depending on the electrical properties (conductivity and permittivity) of the particles and suspending medium. The magnitude and direction of dielectrophoresis depend on polarisability between particles and medium (Clausius-Mossotti factor), strength of applied AC electric field, frequency and the size of particles. The real part of the CM factor reaches a low frequency limiting value, it depends solely on the conductivity of the particles and medium. If we could decide conductivity of the particles, we can know the direction of dielectrophresis.
The microelectrode structures provide the route by which sufficient field strengths can be generated in order to move sub-micrometer particles without requiring high voltage signal generates. In order to understand the relationship between field geometries and particle behavior, we restrict ourselves to two widely-used electrode design, namely the polynomial electrode, and we use the numerical solutions for the electric field have been calculated using commercial finite element method software.
There is two ways for deciding conductivity of particles, (1) when a particle is immersed in an electrolyte, the region of liquid near to the interface has a higher density of counter ions (electric double layer), and conductivity of particles depends on surface conductance which produced by EDL. (Surface conductance is the function of zeta potential) (2) because the conductivity is proportional to the concentration of medium, so we fix the concentration of particles, and vary the one of medium. Trying to find the difference of conductivity of suspension and medium which equals to zero, this point is the conductivity of particles. Final we use DEP to separate particles, find the crossover frequency (translational area of positive and negative DEP), get conductivity of particles to compare that result of two way. For modified latex beads, measurement of zeta potential for conductivity of particles is corresponding to result, and the way of difference of suspension and medium has similar result for different sample, last way may not be suitable for surface modified or small conductivity sample.
|
|---|
