Magnetic and Multifunctional Magnetic Nanoparticles in Nanomedicine: Challenges and Trends in Synthesis and Surface Engineering for Diagnostic and Therapy Applications

Today, the nanotechnology has achieved a development level reaching a stage where it is possible to produce and specially tailor the functional properties of nanoparticles (NPs) for biomedical and biotechnological applications (Gupta et al., 2007; Gupta & Gupta, 2005; Pankhurst et al., 2009). Among different types of NPs, magnetic (MNPs) and more recently, multifunctional magnetic nanoparticles (MFMNPs) have attracted a great deal of attention in nanomedicine over the past decade. These functionalized nanomagnets can be directly injected onto the body vessels and properly manipulated by an external magnetic force. The action at a distance and the non invasive technique provide tremendous advantages for these NPs uses, making these nanomaterial ideal for either in vitro or in vivo biomedical applications (de Dios & Díaz-Garcia, 2010; Lu et al., 2007; Salgueirino-Maceira & CorreaDuarte, 2007). In the biomedicine area, their applications including magnetic resonance contrast agent in Magnetic Resonance Imaging (MRI), magnetohyperthermia for cancer treatment, magnetic force-assisted drug delivery, tissue repair, cell and tissue targeting and transfection, and protein isolation (Lu et al., 2007; Sanvicens & Marco, 2008; Varanda et al., 2008). In this context, the combination of nanotechnology and molecular biology has developed into an emerging new class of nanomagnetics for biomedicine, which combine the MNP properties and the most modern surface engineering techniques resulting in biocompatible and bioselectable MFMNPs (de Dios & Díaz-Garcia, 2010; Majewski & Thierry, 2007; Salgueirino-Maceira & Correa-Duarte, 2007; Selvan et al., 2010). Down to the nanoscale, on the order of around two dozen or less, the magnetic particles change from paramagnetic to superparamagnetic (SPM) behavior, where magnetic moment of the particle as a whole is free to fluctuate in response to thermal energy, while the individual atomic moments maintain their ordered state relative to each other. Thus, the superparamagnetic NPs can only be magnetized in the presence of an external magnetic field and do not retain any magnetism after removal of the magnetic field, which makes