Synthesis And Characterization Of Gold-coated Magnetic Nanoparticles

nanocomposite materials containing a magnetic core and another shell have attracted much interest from material science. The shell structure can improve the physical and chemical properties and have many applications because the shell can overcome the magnetic nanoparticles problems of lack of functional groups and tendency of agglomeration . Gold has become a favored coating material because of its simple synthetic procedure, good chemical stability and nontoxicity. In particular, the surfaces of gold nanoparticles may be functionalized with thiolated organic molecules. Placement of a functional group on the terminal end of the alkanethiolate imparts further chemical reactivity and the opportunity to create multifunctional, reactive nanoparticles. The magnetic nanocomposite with gold coating can be used to targeted drug delivery, cell separation, DNA detection and so on.We synthesized dispersed Fe3O4/Au nanocomposites in aqueous by Frens method. Fe3O4 nanoparticles with 6-8nm in diameter were prepared by co-precipitation and tetramethylammonium hydroxide (TMAOH) was used to disperse the Fe3O4 nanoparticles in aqueous. Dropping time of ammonia solution and dispersing time of TMAOH were found to have influence on magnetism and dispersion of Fe3O4 nanoparticles. The magnetic fluid with good properties of dispersion and magnetism were prepared by choosing the optimum dropping time and dispersing time. The Fe3O4 nanoparticles were coated with gold by Frens method. In the coating process, 3-mercaptopropionic sodium (MPA-Na) was injected to link the functional group COONa to the surface of the Fe3O4/Au nanocomposites. We studied the content of the functional group on the surfaces, the optical and the magnetic properties, and the shape of the Fe3O4/Au nanocomposites.The well-dispersed gold-coated nanoparticles with magnetic core were synthesized in quaternary CTAB (cetyltrimethylammonium bromide)/octane/butanol/water reverse micelles. In our present protocol, aqueous SPION were introduced into water droplets directly as nucleation centers for the subsequent formation of metallic shell via NaBH4 reduction of Au3+ ions on their surfaces; and 3-mercaptopropionic acid (MPA) was chosen to play roles of separating nanoparticles from destroyed reverse micelles system and stabilizing the as-prepared gold-coated magnetic particles in organic media. TEM images show that these MPA-capped core-shell structured nanoparticles are self-assembled into 2D and 3D structures on carbon-coated copper micro-grid. XRD, EDAX, UV-vis and VSM were also exploited to characterize these nanoparticles.