Preparation And Application Of The Magnetic-optical Bifunctional Core-shell Nanomaterials

Magnetic nanoparticles have shown broad application prospects in biomedical field, including targeted drug delivery system, magnetic resonance imaging (MRI), cellular and bio-molecular separation, and immune detection, because of their unique magnetic properties (such as superparamagnetic and high saturation magnetization), good biocompatibility and low toxicity. Therefore, they have attracted great interests in recent years. To broaden the application of magnetic nanoparticles in various fields, a series of surface modifications were carried out to fabricate functional materials. According to the literature, the magnetic nanoparticles modified by optical materials can produce the magnetic-optical bifunctional nanomaterials with excellent magnetic and luminescent properties, which are widely used in magnetic, fluorescent, biological and pharmaceutical fields, especially with attractive prospect for application in the ultra-high density data storage, bio-molecular recognition, drug delivery, etc. This thesis mainly studies the preparation of Fe3O4 and CoFe2O4 magnetic nanoparticles, silica coating and modification with luminescent materials, as well as the applications of the nanocomposites in MRI. The contents of this thesis include three chapters.Chapter 1 summarizes the synthesis, modification and application of magnetic nanoparticles, the preparation and application of core-shell structural magnetic/silica nanoparticles and magnetic-optical bifunctional nanomaterials. The research envisagement for the whole thesis was also proposed.In chapter 2, First, Fe3O4 nanoparticles were synthesized in different alcohol-water solvent systems by a facile chemical coprecipitation process using ammonia as precipitant, FeCh·6H2O and FeCl2·4H2O as Fe sources. The nanoparticles were then characterized by TEM (transmission electron microscopy) and XRD (X-ray diffraction) techniques. Along with the decrease of polarity and the increase of viscosity of the solvent systems, the morphology of Fe3O4 nanoparticles changed from spherical to rod-like structure, the particle size increased, and the dispersion of the nanoparticles was improved. The produced nanoparticles can be well re-suspended in water. The surface modification of Fe3O4 nanoparticles synthesized in ethanol-water system was carried out using oleic acid as surfactant. After surface modification with oleic acid, the nanoparticles can be transferred from aqueous phase to organic phase.Second, chemical co-precipitation method was employed to synthesize Fe3O4 nanoparticles which can be well dispersed in water by using citric acid as a surfactant. The as-synthesized Fe3O4 nanoparticles showed a good superparamagnetic property with high saturation magnetization (Ms=50.2 emu/g). The r1 and r2 relaxivities of as-synthesized magnetite nanoparticles are found to be r1 (13.64 Fe mM-1 s-1) and r2 (119.74 Fe mM-1 s-1), respectively. Such values for r1 and r2 suggest that the as-synthesized magnetite nanoparticles can act as both T1 and T2 contrast agents. Afterwards, by using Fe3O4 nanoparticles with citric acid as a surfactant as seeds in a Triton X-100/hexanol/cyclohexane/water reverse microemulsion system, the core-shell structural Fe3O4@SiO2 nanocomposite particles were prepared via hydrolysis and condensation of tetraethyl orthosilicate (TEOS) under the catalysis of alkali. The effects of different stirring methods and the concentration of TEOS on the morphology of Fe3O4@SiO2 nanoparticles were investigated. The results showed that the mechanical stirring could effectively control the morphology of the composite nanoparticles to form a good dispersion and spherical morphology of core-shell nanoparticles. With the increase of TEOS concentration, the thickness of the SiO2 shell layer increases, and the morphology of the obtained composite particles become more uniform.Finally, the Fe3O4@SiO2 nanoparticles were subsequently modified with 3-aminopropyl-triethoxysilane (APTES) to to immobilize amino groups onto the particle surfaces, then dansyl groups were chemically attached onto the nanoparticles by nucleophilic substitution of sulfonyl chloride with primary amines, resulting the formation of magnetic-optical bifunctional Fe3O4@SiO2@APTES-Dy nanocomposites. Extensive characterizations of the obtained nanocomposites have been performed using TEM, FT-IR spectra, UV-vis spectra, XRD and X-ray photoelectron spectroscopy (XPS). Their magnetic and fluorescent properties were also studied. To investigate their possible applications in biology and medicine fields, the cell toxicity and MRI of the Fe3O4@SiO2@APTES-Dy composites were determined. The results showed that the nanocomposites could be used as excellent T2 contrast agents of MRI due to their good effect of MRI and very low toxicity. TEM observations of the cells incubated with the nanoparticles showed that the Fe3O4@SiO2@APTES-Dy nanocomposites could be endocytosed by the cells and then distributed in the endosome and cytoplasm.In chapter 3, we tried to use co-precipitation, solvothermal method, and thermal decomposition to prepare cobalt ferrite (CoFe2O4) nanoparticles. Although water-soluble CoFe2O4 nanoparticles could be prepared by chemical co-precipitation, their larger particle size was not convenient for silica coating, which limited their biological applications. CoFe2O4 nanoparticles prepared by the solvothermal process were composed of two kinds of particles. Some are well-dispersed small size nanoparticles, and others are large flower-like particles consisting of several small nanoparticles. The as-synthesized CoFe2O4 nanoparticles prepared by solvothermal process have a good super-aramagnetic property and their saturation magnetization Ms=53.2 emu/g. Their r2 relaxivity was found to be 36.54 Fe Mm-1 s-1 from MRI. Such a value for r2 suggests that the as-synthesized magnetite nanoparticles can act as T2 contrast agents.CoFe2O4 nano-particles prepared by thermal decomposition showed an average diameter of about 5 nm, and it is easier to coat them with silica layer resulting the core/shell structural CoFe2O4@SiO2. After silica coating, the oil-soluble CoFe2O4 nanoparticles easily dissolved in water. The CoFe2O4@SiO2 nanoparticles were subsequently modified with APTES to introduce amino groups on their surfaces, and then the magnetic-optical bifunctional CoFe2O4@SiO2@APTES-Dy nanoparticles were obtained by the nucleophilic substitution reaction between the surface amino groups and dansyl chloride.Extensive characterizations of the produced nanocomposites have been performed by using a variety of microscopy and spectroscopic techniques. The cell toxicity and MRI studies of the as-prepared CoFe2O4@SiO2@APTES-Dy nanocomposites showed that the composite nanoparticles with very low cell toxicity might function as an excellent T2 contrast agent of MRI.