Preparation And Properties Of Superparamagnetic Iron Oxide Nanoparticles

Magnetic nanoparticles display great applications in many fields due to their unique properties such as surface effect, small-size effect, quantum-size effect and specific magnetism. They have been developed to be the important tools for the diagnosis, the treatment, the separation of the specific pathogens and biological species. They provide a new platform and opportunity for the biomedical applications like medical imaging, immunological detection and drug delivery, and have been widely studied and used in biomedicine. They are the ideal probe of biomedical examination because the unique magnetism can induce the signals that can not be tested in the biological system. Stable and nontoxic magnetic nanoparticles can be mediated by the external magnetic field after the surface modification. This can make the nanoparticle itself have the capacity of the non- invasive targeting tool and be used in the nuclear magnetic resonance(NMR) and magnetic resonance imaging(MRI). Thus, it is of great significance to study the magnetic nanocomposites. In this paper, the preparation and surface modification of the magnetic nanoparticles would be systematically studied, including the structure, morphology, magnetic properties and the relaxation performance of several materials under the ultralow field.Here, coprecipitation method and high-temperature pyrolysis method have been employed to prepare the iron oxide nanoparticles. The morphologies, structures, sizes and magnetic properties of theas-prepared samples were characterized by transmission electron microscopy, X-ray diffraction, infrared spectroscopy, laser particle size analyzer and magnetometer. The contrast of the magnetic nanoparticles prepared by the two different methods showed that the nanoparticles prepared by the high-temperature pyrolysis method had regular morphology, good crystalline and particle size, and good crystal quality. Therefore, the high-temperature pyrolysis have been chosen to prepare the magnetic nanoparticles for the subsequent studies.In this work, the effect of different molar ratios(1:8, 1:6, 1:4.5, 1:3) of oleic acid and oleyl alcohol on magnetic nanoparticles’ particle sizes have been explored. The results of the laser particle size analyzer indicated that the particle sizes of the magnetic nanoparticles increased while the oil alcohol was used less. The effects of different solvents(diphenyl ether and octadecene) on magnetic nanoparticles’ diameters were studied as well. The images of TEM revealed that the nanoparticles diameter prepared by diphenyl ether were smaller than that prepared by octadecene, was 3 nm and 12 nm, respectively.The oleic acid on the surface of the nanoparticles were ligand-exchanged with the small organic molecules such as dopamine and 3,4-hydroxy acid(DHCA).The images of TEM showed that there were no obvious difference of the morphologies and sizes of the nanoparticles pre- modification and post-modification. The modified magnetic nanoparticles could be well dispersed in the aqueous phase. Thus, Fe3O4-DHCA were functionalized by polyethyleneimine(PEI) to explore the preparation conditions of reactions as well as the structures and magnetic properties changes of the magnetic nanoparticles before and after modification.A Michael addition of dopamine- modified magnetic nanoparticles and methyl acrylate were performed, and reacted with ethylenediamine to obtain the composites of different generations of magnetic nanoparticles/polyamide amine. The structural changes of different generations of magnetic nanoparticles-dendrimers were studied. The results showed that the complex got more amino active sites with the increase of the generation.The relaxation behaviors of the two magnetic nanoparticles with different sizes(3 nm and 12 nm) modified by dopamine have been studied in the ultralow field(10 m T). The influence of the magnetic nanoparticles on the water protons in ultra- low field has been obtained to exhibit that the smaller the particle size is, the shorter the longitudinal relaxation time is; and the relaxation time is shorter while the concentration is increasing.