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Magnetic nanoparticle |
Magnetic nanoparticles are a class of nanoparticle which can be manipulated under the influence of a magnetic field. Such particles commonly consist of magnetic elements such as iron, nickel and cobalt and their chemical compounds. These particles have been the focus of much research recently because they possess attractive properties which could see potential use in catalysis 1, biomedicine 2, magnetic resonance imaging 3, data storage 4 and environmental remediation 5.
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The wide range of magnetic nanoparticles that have been synthesized has given rise to a variety of different physical and chemical properties largely depending on the synthesis method and chemical structure. In most cases, the particles range from 1 - 100 nm in size and display superparamagnetism.6
The established methods of magnetic nanoparticle synthesis include:
Co-precipitation is a facile and convenient way to synthesize iron oxides (either Fe3O4 or γ-Fe2O3) from aqueous Fe2+/Fe3+ salt solutions by the addition of a base under inert atmosphere at room temperature or at elevated temperature. The size, shape, and composition of the magnetic nanoparticles very much depends on the type of salts used (e.g.chlorides, sulfates, nitrates), the Fe2+/Fe3+ ratio, the reaction temperature, the pH value and ionic strength of the media.6
Monodisperse magnetic nanocrystals with smaller size can essentially be synthesized through the thermal decomposition of organometallic compounds in high-boiling organic solvents containing stabilizing surfactants 6.
Using the microemulsion technique, metallic cobalt, cobalt/platinum alloys, and gold-coated cobalt/platinum nanoparticles have been synthesized in reverse micelles of cetyltrimethlyammonium bromide, using 1-butanol as the cosurfactant and octane as the oil phase. 6
A wide variety of applications have been envisaged for this class of particles these include:
Scientists at Georgia Tech have developed a potential new treatment against cancer that attaches magnetic nanoparticles to cancer cells, allowing them to be captured and carried out of the body. The treatment, described in the Journal of the American Chemical Society (July 9, 2008), has been tested in the laboratory on mice and will be looked at in survival studies.78
Magnetic immunoassay9 (MIA) is a novel type of diagnostic immunoassay utilizing magnetic beads as labels in lieu of conventional, enzymes , radioisotopes or fluorescent moieties.
Magnetic storage has played a key role in audio, video and computer development since its invention more than 100 years ago by Valdemar Poulsen . In 1956 IBM built the first magnetic hard disk drive featuring a total storage capacity of 5 Mbytes at a recording density of 2 kbits/in2. Since then the density of bits stored on a surface of a disk has increased by 35 million fold to current densities of 70 Gbits/in2 and has been doubling every year over the past five year. At such densities, the bits must be positioned on the disk with nanometer resolution. Present magnetic disk drives are based on longitudinal recording systems where the magnetization of the recorded bit lies in the plane of the disk. These systems contain a recording head composed of a separate read and write element, which flies in close proximity to a granular recording medium. The recording media signal-to-noise ratio (SNR) needed for high-density recording is achieved by statistically averaging over a large number of weakly interacting magnetic grains per bit.
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