Synthesis Of Superparamagnetic Nanoparticles For Magnetic Resonance Imaging Contrast Agents

Magnetic nanoparticles have been of scientific and technological interest because of their unique magnetic and electric properties. Among them, superparamagnetic nanoparticles with have exhibited widespread applications in many traditional areas such as ferrofluid, high-density information storage, gas sensors and catalysis. Moreover, they also show great potential applications for many important biomedical areas such as magnetic resonance imaging (MRI) contrast agents, drug delivery, cell labeling and magnetic separation due to their large specific surface area, low toxic and high chemical stability.Because most of the commercial MRI contrast agents have some disadvantages including weak magnetic response, limited targeting ability and difficult to achieve single cell labeling,etc. Herein, a high temperature polyol process has been developed to synthesize biocompatible superparamagnetic nanoparticles. The as-prepared magnetic nanoparticles with controlled size (5-10nm) exhibit high stability, crystalline and saturation magnetization. Moreover, the polymer shell outside the nanoparticles also serves as a versatile platform for chemical modification and bioconjugation. As a result the magnetic nanoparticles prepared by this approach are an excellent MRI contrast agents. The main results achieved in this disquisition are listed as below:(1) Fe₃O₄ nanoparticles were successfully synthesized in liquid polyols via high temprature hydrolysis of chelate metal alkoxide complexes and thermal decomposition of Fe(acac)3. The structure and morphology of the Fe₃O₄ nanoparticles were investigated by XRD, TEM, SAED, DLS and FTIR. The magnetic properties of the samples were measured by VSM. It was indicated that the as-prepared Fe₃O₄ nanoparticles obtained by the two above mentioned methods were both cubic crystal structure with core size of 5-10 nm narrow size distribution and high monodispersibility in aqueous solution. The polymer shell outside the Fe₃O₄ nanoparticles with thickness of 30-40 nm resulted in good colloid stability and biocompatibility for the magnetic nanoparticles. Moreover, the two samples both exhibited superparamagnetic behavior with high saturation magnetization at room temperature, which was influenced by their sizes and crystallinzations. Comparing with the sample prepared by high temprature hydrolysis of chelate metal alkoxide complexes, the sample prepared via thermal decomposition of Fe(acac)3 had higher saturation magnetization. The Fe₃O₄ nanoparticles modified by PAA was the highest one with the value of 68 emu/g, which was higher than the previous report. MRI experiment indicated that the as-synthesized products showed the good contrast performance, in particular, the PVP modified nanoparticles. In addition, the effects of the growth conditions such as modification agents and their amount, temperature, time, concentration of reactants on the size, monodispersibility and magnetic properties of Fe₃O₄ nanoparticles were investigated.(2) The cubic CoFe₂O₄ nanoparticles with core size of 5-10 nm were fabricated in liquid polyols via high temprature hydrolysis of chelate metal alkoxide complexes and thermal decomposition of Fe(acac)₃/Co(acac)₂, respectively. Moreover, they possessed the narrow size distribution, high monodispersibility in aqueous solution, good colloid stability and biocompatibility because of the polymer shells on the surface of nanoparticles. At room temperature, the two samples showed the superparamagnetic properties with high saturation magnetization, which was influenced by their sizes and crystallinzations. The sample prepared via thermal decomposition of Fe(acac)₃/Co(acac)₂ had higher saturation magnetization than that obtained by high temprature hydrolysis of chelate metal alkoxide complexes. Furthermore, the effects of the growth conditions such as modification agents and their amount, temperature, time, concentration of reactants on the size, monodispersibility and magnetic properties of CoFe₂O₄ nanoparticles were investigated.