Magnetic Nanoparticles for Biomedical Applications: Synthesis, Characterization and Uses
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Fabrication of nanoparticles can be grouped into three main synthetic methods: solid, gas, and solution. The solid route involves the mechanical milling or the mechanochemical synthesis of raw powder to produce nanoparticles. This method has the disadvantage of introducing contamination to the products from the milling equipment as well as producing particles with wide size distribution. In gas and chemical routes, the synthesis can be considered as either “phase-transformation” or “phase-build-up.” The “phase-transformation” can be described as the conversion of finely divided metal compounds into metals through thermal decomposition (see later) or chemical reduction. On the other hand, in “phase-build-up,” particles are “constructed” from building blocks (metal atoms). This process can take place from the gas phase (chemical or physical vapor deposition) or from the liquid phase (chemical precipitation). Gas-phase synthesis involves the formation of a supersaturated vapor of condensable gaseous species as a result of a chemical reaction that produces a new species or as a result of a physical process such as cooling that will reduce the vapor pressure of the condensable species. There are also several methods that use the solution route and are discussed in further detail later. These techniques produce uniform nanoparticles of different shapes by using appropriate precursors and by adding a surfactant or a capping ligand during the transformation. The addition of a surfactant/capping ligand can also prevent aggregation of the particles.