Preparation And Magnetic Resonance Properties Of SiO₂Coated Superparamagnetic Fe₃O₄Nanoparticles

Superparamagnetic iron oxide nanoparticles have been widely used in biomedicalfield owing to their unique physical and chemical properties. The Fe3O4nanoparticleswith modispersed, stable in aqueous solutions and biocompatibale properties arenecessity and key point for its application in biomedical fields. In this thesis, firstly thesuperparamagnetic Fe3O4nanoparticles prepared by a polyol method were modifiedvia different dispersants. The obtained nanoparticles are uniformed and monodispersedin water. Secondly, the nanoparticles were coated by SiO2through an elemental siliconpowder oxidation method in different reaction conditions. Thirdly, the stability andmagnetic resonance properties of Fe3O4@SiO2composite nanoparticles with singlecore were investigated. The main contents and major results are given as follows:1. Fe3O4nanoparticles were prepared by the polyol method using Fe(acac)3asprecursor and triethylene glycol as solvent. The results show that the obtained Fe3O4nanoparticles are uniform particle size, high purity, good crystallinity, high saturationmagnetization, and also possess superparamagnetism at room temperature. Thensodium hexametaphosphate, sodium pyrophosphate, sodium tripolyphosphate, sodiumcitrate were used as dispersants to disperse the Fe3O4nanoparticles in aqueous solution,respectively. The results indicate Fe3O4nanoparticles dispersed in aqueous solution bythe phosphates are more stable than by sodium citrate.2. The synthesis of core-shell Fe3O4@SiO2composite nanoparticles wasperformed by an elemental silicon oxidation process in the presence of Fe3O4nanoparticles with sodium tripolyphosphate. The process involved two main reactions:(i) silanol monomers are formed by the oxidation reaction of silicon powder and (ii)SiO2are formed by a condensation polymerization reaction.The influence of catalyst,dosage of silicon powder, reaction temperature and reaction time on quality ofFe3O4@SiO2composite nanoparticles was explored. The results conclude that the balance between the silanol monomers production and its consumption to suppress thehomogeneous nucleation of SiO2is the key to preparing high quality core-shellFe3O4@SiO2composite nanoparticles.3. The single-core structured Fe3O4@SiO2composite nanoparticles prepared viathe elemental silicon powder oxidation approach have a uniform size distribution andcan be dispersed excellently in aqueous solution and RPMI-1640cell culture medium.The influence of the thickness of SiO2shell on the relaxation properties ofFe3O4@SiO2composite nanoparticles was studied.It have been found that longitudinalrelaxation rate of Fe3O4@SiO2composite nanoparticles are sharply decreased afterSiO2coated, as well as transverse relaxation rate are reduced depend on the increasingof the SiO2layer thickness of Fe3O4@SiO2composite nanoparticles.