Controllable Synthesis Of Magnetite Nanoparticles And Nanocrystal Clusters For Application In Magnetic Resonance Imaging

Magnetic iron oxide nanoparticles have been widely used as contrast agent in magnetic resonance imaging (MRI), owing to their significant enhancement on the relaxation of protons. The efficiency of magnetic nanoparticles as contrast agent is usually quantified by the transverse relaxivity of the particles suspension. The transverse relaxivity is closely related with the physicochemical properties of magnetic nanoparticles, such as the size, surface property, magnetic property, and so on. The main challenge for the application of magnetic nanoparticles in this area is how to precisely tune the physicochemical properties of materials in a controllable way. In this dissertation, we have synthesized a series of magnetite nanoparticles and nanocrystal clusters with tunable properties and used them as contrast agents in MRI.We have developed a novel flocculation-redispersion method to synthesize superparamagnetic magnetite nanoparticles. By controlling the flocculation and release of magnetite nanoparticles in aqueous solution, the magnetite nanoparticles with size of ⁵ nm can be separated and purified by magnetic sedimentation conveniently. It greatly simplifies the post-processing in the production of the commercial superparamagtnetic contrast agent and avoids the tedious ultrafiltration process. After conjugation with monoclonal antibody, the magnetite nanoparticles have been used in the molecular diagnosis of tumor in mice in vivo and the desired result has been achieved. To improve the magnetization and uniformity of magnetite nanoparticles, we synthesized the magnetite nanoparticles with sizes ranging from 5³5 nm by a facile polyol process. The effects of the parameters on the properties of magnetite nanoparticles, have been studied carefully to obtain the efficient tools for tailoring the physicochemical properties of magnetite nanoparticles. The as-synthesized magnetite nanoparticles, with uniform size and high magnetization, possess the higher transverse relaxivity (263 mM^-1s^-1) than that of magnetite nanoparticles synthesized by traditional coprecipitation method (<200 mM^-1s^-1).We have developed a facile polyol process to synthesize the magnetite nanocrystal clusters with ultra-high magnetic content and hydrophilic surface. A new mechanism based on the interaction between the repulsion force and surface tension has been introduced to explain the formation of magnetic nanospheres in polyol process. By varying the reaction parameters to break the balance between the repulsion force and the surface tension, we obtained a series of magnetite nanospheres with sizes ranging from 30 to 450 nm. The structure and surface property of the nanospheres can be tuned tby the same way, too.The valuable exploration has been carried out on the relationship between the transverse relaxivity of magnetic nanospheres suspension and the diameter of the nanosphere. The transverse relaxivity of suspensions of magnetite nanospheres with size of 60 nm is 665 mM^-1s^-1, which is the highest value being published up to date. The synthesized magnetite nanopsheres with different coating materials have been used as cellular probe to visualize the cells in vitro and in vivo and the expected result has been proved by MRI.