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Dielectrophoresis (DEP) force is generated by dielectrically polarized particles in non-uniform electrical fields. In this paper, we report the use of DEP in microfluidic sample preparation. The chip uses DEP force to concentrate mammal cells and magnetic beads, in order to extract and purify mRNA from these cells. Both the mammal cells and magnetic beads exhibit negative DEP properties and are concentrated in the same region in the electrical field ie. regions of weaker electrical field of the chip. Therefore, the magnetic beads coated with Oligo (dT) can easily capture mRNA released from the cells when cell is lysed by chemical lyse. Thus a high mRNA yield can be obtained. Silicon is used to make the chip channel and the DEP electrodes. The working principle of the micro-fluidic chip, its fabrication process and experiment results are described in this report.

The hollow silica/cobalt ferrite (CoFe₂O₄) magnetic microsphere with amino-groups were successfully prepared via several steps, including preparing the chelating copolymer microparticles as template by soap-free emulsion polymerization, manufacturing the hollow cobalt ferrite magnetic microsphere by in-situ chemical co-precipitation following calcinations, and surface modifying of the hollow magnetic microsphere by 3-aminopropyltrime- thoxysilane via the sol-gel method. The average diameter of polymer microspheres was ca. 200 nm from transmission electron microscope (TEM) measurement. The structure of the hollow magnetic microsphere was characterized by using TEM and scanning electron microscope (SEM). The spinel-type lattice of CoFe₂O₄ shell layer was identified by using XRD measurement. The diameter of CoFe₂O₄ crystalline grains ranged from 54.1 nm to 8.5 nm which was estimated by Scherrer's equation. Additionally, the hollow silica/cobalt ferrite microsphere possesses superparamagnetic property after VSM measurement. The result of BET measurement reveals the hollow magnetic microsphere which has large surface areas (123.4m²/g). After glutaraldehyde modified, the maximum value of BSA immobilization capacity of the hollow magnetic microsphere was 33.8 mg/g at pH 5.0 buffer solution. For microwave absorption, when the hollow magnetic microsphere was compounded within epoxy resin, the maximum reflection loss of epoxy resins could reach -35dB at 5.4 GHz with 1.9 mm thickness.