Preparation and characterization of polymer-coated core-shell structured magnetic microbeads

Composite microbeads consisting of polymer-coated iron oxide nanoparticles are prepared by. the microemulsion polymerization of styrene, divinyl benzene and methacrylic acid in the presence of emulsifiers. Fourier transform infrared spectrometer analysis indicates the presence of -COOH groups and Fe3O4 of the microbeads: The amount of COOH groups localized on the surface, which is about 0.15 mmol/g, is determined by. conductometric titration. Transmission electron microscope picture reveals that the microbeads have a core-shell structure. The dissolving experiments of microbeads in hydrochloric acid and toluene further identify the core-shell structure. Optical microscope indicates that the magnetic microbeads have uniform and spherical forms with the size of 1-5 mum. Magnetic sensitivity measurement indicates that the microbeads can be used conveniently. Magnetic property measurement shows very little residual magnetization and coercivity, which are below 0.5 emu/g and around 15 Oe, respectively. The magnetic properties are greatly related to the particle sizes. The thermal gravity analysis result shows the improvement of thermal stability. The experiment of immobilized antibody indicates that the functional groups on the surface are appropriate. (C) 2003 Elsevier Science B.V. All rights reserved.