| As a new functional material, magnetic particles have developed quickly in recent years. It's applications in immunoassay lead to a new idea for bioseparation and detection. The development of magnetic particles with functional unites was described in this paper, and explained it's application in cell separation, fixation of enzyme, target presenting, protein purification, nucleic acid separation and clinical diagnosis. The aim of this thesis is to prepare magnetic fluids, Fe3O4/SiO2 and Fe3O4/Au composite functional particles, the preparation principle of present conditions was discussed and their chemical and physical characteristic was analysed comprehensively. First we used chemical coordination precipitation method prepared the magnetic particles with hydriphilicity. Some factors that would influence the result were discussed in particular, such as method of adding alkal, interaction temperature and time, concentration of regents and so on. The particlesize was tested with TEM; the crycal construction was analysed with X-ray diffraction instrument, the magnetic property was charactered by magnetic balance and transmittance of suspension in given time and magnetic field. The results show particles'diameter is 35nm, XM is 3.62×10-4cm3·g-1. Stable magnetic fluids were prepared by absorbing sodium oleate on Fe3O4 surface, the mechanism and condition of absorption was discussed. The Fe3O4/SiO2 composite particles are obtained through hydrolyzing sodium silicate, and O-Si bond was produced on the surface of Fe3O4 particles. The composite particles are characterized by a range of techniques including TEM, infrared spectra, magnetic balance and spectrophotometer. The Fe3O4/SiO2 composite particles was applied in separation of plasmid DNA from lysates, and the high purity and efficiency proved the Fe3O4/SiO2 composite particles can be used in bioseparation. We produced Fe3O4/Au core-cell composite particless by means of Frens method combined with seed-growth method, discussed the deoxidization mechanism of Au atoms congregating on the surface of Fe3O4 particles, analysed the effect of Fe3O4 seeds number on Fe3O4/Au particlesize. The UV spectra show absorption peak in evidence, which is character peak of nanogold, proved the produced particles'surfaces were covered by Au. In addition, the results showed the Fe3O4/Au particles'diameter is about 70nm, and it can respond quickly in magnetic field. Finally, we prospected the application of Fe3O4/SiO2 and Fe3O4/Au composite functional particles, and presented extend content of this thesis.
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