| Summary: | Magnetic nanoparticles have attracted a great attention due to their diverse potential applications in biology and technology and a substantial number of synthetic methods have been developed to produce these materials. Chemical synthesis approaches have been a particular focus of the field, because of their ability to tune the size, shape and composition, as well as surface of the nanoparticles. To produce magnetic nanoparticles for biomedical applications, one of the primary requirements is to make nanoparticles that are dispersible and stable in aqueous medium under physiological conditions. The focus of this thesis has been the development of methods to synthesise magnetic nanoparticles of different compositions and shape that are dispersible and stable in water. Monodisperse water-dispersible magnetic Co nanoparticles were fabricated using a facile reduction method in water in the presence of hydrophilic polymers. The size and shape of the nanoparticles were both tunable by varying the conditions of synthesis. The size of the spherical nanoparticles would be tuned between 2-7.5 nm by changing the concentration of the polymer. The synthesis approach could also be used to produce nanorods of 15 x 36 nm. The spherical nanoparticles were superparamagnetic at room temperature and were stable in water and in electrolyte solutions of up to 0.23 mM NaCI. The preliminary use of the Co nanoparticles as a MRI contrast enhancer was tested and provided evidence that these materials have considerable potential in this application. Using a similar method, water-dispersible and colloidal stable CoPt nanoparticles were prepared. The effect of structure, functional group and combinations of stabilising ligands on the morphology of the nanoparticles was investigated. It was found that multiple-thiol functional groups play a critical role in the formation of hollow nanoparticles. The size of hollow nanoparticles could be tuned in the range of7-54 nm by changing the concentration and molecular weight of the ligands. The hollow nanoparticles were water-dispersible and superparamagnetic at room temperature. They were stable in wide range of pH from I to 12.5 and at electrolyte concentrations as high as 2 M NaCI. An experiment on tracking stem cells labelled with the CoPt hollow nanoparticles indicated that MRl can effectively detect low numbers of labelled cells due to the enhanced contrast provided by the nanoparticles. CoPt hollow nanoparticles may, thus, have potential applications in MRI. CoFe and cobalt ferrite nanoparticles were synthesised by thermal decomposition in organic solvent to take advantage of the superior control over monodispersity and morphology of the nanoparticles afforded by solvent based syntheses. In the case of CoFe nanoparticles, a layer of Pt was also deposited on the nanoparticles to make core/shell structures. Varying reaction conditions, such as reaction time, had an insignificant effect on monodispersity, size and shape of Co Fe nanoparticles. However, these parameters had a substantial impact on the cobalt ferrite nanoparticles. Cobalt ferrite nanoparticles with sizes in a broad range from 4 nm to over 30 nm and diverse shapes including spherical, cubic and star-like, were synthesised by changing surfactant concentration and reaction time. Ligand exchange using hydrophilic silane and/or polymer ligands were demonstrated to be efficacious on CoFe, CoFelPt and cobalt ferrite nanoparticles. After ligand exchange, the nanoparticles were reasonably stable in water. The work presented in this thesis demonstrates that chemical synthesis is an efficient route to the production of magnetic nanoparticles of diverse composition and shape and so magnetic properties. Moreover, these materials were found to be stable in aqueous solutions. However, it is clear that the application of such magnetic nanoparticles in biology and medicine will require substantial further effort in the development of ligand shells able to withstand the rigours of the biological environment. Given the success of chemical synthesis demonstrated in this thesis, the development of ligand shell systems is now a major challenge of the field.
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