Synthesis, Characterization and Manipulation of Cobalt Nanoparticles
G. Cheng and A.R. Hight Walker
CO nanoparticles, synthesis
Magnetic nanoparticles have shown great potential for applications not only in catalysis and magnetic recording, but also in medical sensors and biomedicine. Their biological applications include contrast enhancement agents for magnetic resonance imaging (MRI) and site-specific drug delivery agents for cancer therapies. Here we report on the synthesis of cobalt nanoparticles with controllable sizes and shapes via thermo-decomposition. X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) have been used to characterize these nanoparticles.
We also demonstrate the magnetic-field-induced (MFI) assemblies of cobalt nanoparticles. Under the influence of a magnetic field, cobalt nanoparticles can assemble into linear chains along the direction of the applied field in a colloidal solution. A superconducting quantum interference device (SQUID) magnetometer is used to measure the magnetic properties of cobalt nanoparticles in a colloidal solution. A transition is observed between two different spin rotation mechanisms, Néel rotation at lower temperatures when the solvent freezes and Brownian rotation at higher temperatures when the solvent melts.
In order to fully realize the biological applications of these magnetic nanoparticles, one needs to develop the methods for improving their bio-compatibility. Here we present the synthesis of cobalt/gold and cobalt/silver bimetallic nanoparticles by growing gold or silver on the pre-synthesized cobalt nanoparticles. These bimetallic nanoparticles are expected to maintain their magnetic properties of cobalt nanoparticles, while gold or silver can improve their biocompatibility. However, gold or silver can also diffuse into cobalt nanoparticles, alter the crystalline structure of cobalt nanoparticles, and therefore, change the magnetic properties of cobalt nanoparticles.
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Nanotech 2006 Conference Program Abstract