Synthesis and charaterization of coated and uncoated magnetic nanoparticles

Abstract

Magnetic nanoparticles have been proposed for use as biomedical purposes to a large extent for several years. In recent years, nanotechnology has developed to a stage that makes it possible to produce, characterize and specifically tailor the functional properties of nanoparticles for clinical applications. This has led to various opportunities such as improving the quality of magnetic resonance imaging, hyperthemic treatment for malignant cells, site-specific drug delivery and the manipulation of cell membranes. To this end a variety of iron oxide particles have been synthesized. A common failure in targeted systems is due to the opsonization of the particles on entry into the bloodstreams, rendering the particles recognizable by the body’s major defense system, the reticulo-endothelial system. The co-precipitation method: nanoparticles comprised of gold shell and magnetite/maghemite inclusion were synthesized by overgrowing the gold shell onto the magnetic seeds using sodium citrates as a reducing agent. Oxidized magnetites (Fe3O4) fabricated by co-precipitation of Fe2+ and Fe3+ in strong alkaline solution were used as magnetic cores. These magnetic nanoparticles were characterized by X-ray diffraction (XRD), Transmission Electron Microscope (TEM), ultraviolet-visible (UV-vis) spectroscopy and Vibrating Sample Magnetometer (VSM). Results from x-ray diffraction show that the gold-iron oxide nanoparticles have a face-centered cubic shape, a=8.39 Å and a special group Fd3-m=227 with the dominant crystal planes of {311}. The gold-coated magnetic nanoparticles exhibited a surface plasmon resonance peak at 520 nm. The nanoparticles are well dispersed in distilled water. The particle size of the magnetite nanoparticles was about 0.5 μm (500 nm) confirmed by transmission electron microscope image. The saturation magnetization of the as-synthesized iron oxide nanopowders was 38 emu/g and the blocking temperatures for magnetization 1, magnetization 2, magnetization 3, and magnetization 4 are 150, 143, 138, and 135 K, respectively. The reverse micelle (Micro emulsion) method: a unique reverse micelle method has been developed to prepare gold-coated iron (Fe@Au) nanoparticles. X-ray diffraction, iv ultraviolet/visible, transmission electron microscope, and magnetic measurements are utilized to characterize the nanocomposites. X-ray diffraction only gives Face-Centered Cubic (FCC) patterns of gold for the obtained nanoparticles and indicated that gold exists as a metal. The absorption band of the iron@gold colloid shifts to a longer wavelength and broadens relative to that of the pure gold colloid. Transmission electron microscope results show that the average size of the iron@gold nanoparticles is about 2 μm (2000 nm) and indicated that the nanocomposite was single-nanosized and has a sharp size distribution. These nanoparticles are self-assembled into chains on micron scale under a 0.5T magnetic field. Magnetic measurements show that the particles are super paramagnetic with a blocking temperature (TB) of 42 K. At 300 K (above blocking temperature), no coercivity (Hc) and remanence (Mr) is observed in the magnetization curve, while at 2 K (below TB), coercivity and remanence are observed to be 728 Oe and 4.12 emu/g, respectively.