Preparation And Biomedical Applications Of Multifunctional Nanocomposites Based On Magnetic Nanoparticles

Because of the nanoscale size and rapid magnetic response, superparamagnetic nanoparticles are of great interest for applications such as contrast-enhancing agents for magneticresonance imaging (MRI), Magnetic fluid Hyperthermia (MFH), magnetically assisted cell sorting and separation. Previous studies have examined semiconductor nano-crystals or quantum dots (QDs) as the optical tag due to their non-bleaching and tunable fluorescent properties. Moreover, noble metals such as Au and Ag have been used as optical markers in scattering-based imaging modalities. Recently, researchers focus on the synthesis of magnetic fluorescent bifunctional nanocomposites and their applications in biology. Although the former method offers several advantages (controlled size and shape, monodispersity, stability, and facilitation), it tolerates the hazardous precursor, high synthesis temperatures, a long reaction time and environmental issues.The objective of this dissertation is to explore a general facile and green approach for the aqueous phase synthesis of fluorescent and magnetic bifunctional nanocomposites based on superparamagnetic nanoparticles, and improve some facile solution-based synthesis methods for the preparation of Ag-Fe3O4nanocomposites and assembly nanorings. The main results were summarized as follows:1. Using hydrazine hydrate as antioxidant and reduction agent, magnetic Fe3O4nanoparticles were successfully prepared via a co-precipitation method. And superparamagnetic Fe3O4nanoparticles were synthesized via a similar method in solution phase at120℃. These superparamagnetic Fe3O4nanoparticles were then encapsulated into liposomes with diameters range from200to400nm.2. We design a facile and green method to synthesize luminescent superparamagnetic nanocomposites with a CdSe/CdS-Fe3O4structure under mild conditions.This approach was performed in a solution-phase at～90℃(Fe3O4) and60℃(CdSe/CdS), respectively. Fe3O4nanoparticles were, prepared via a simple coprecipitation process, used as seeds. A new route was designed to induce CdSe/CdS nanoparticles growing around the seeds for preparing bifunctional nanocomposites of CdSe/CdS-Fe3O4.In this approach, tri-sodium citrate plays an essential role in guiding and maintaining the structure of the nanocomposites. The fluorescence spectrum and M-H loops indicate that the bifunctional nanocomposites were synthesized successfully. It is proved that these bifunctional nanocomposites could be guided with magnetic force in vitro delivery into a human cancer cell line by a fluorescence microscope. The superparamagnetism and the high Ms (61.78emu/g) of Fe3O4nanoparticles suggest that these nanocomposites also can be used as a Tj Magnetic Resonance Imaging (MRI) contrast agent. The MRI images indicate that these bifunctional nanocomposites have the potential applications for diagnostic as a72MRI contrast agent.3. Ag-Fe3O4nanocomposites were successfully synthesized by means of reducing Ag+and Fe3+simultaneously under a mild condition. In this work, tri-sodium citrate was used as surfactant and conjugation agent, and hydrazine hydrate were used as reduction agent. The XRD and HRTEM data reveal that the formation of nanocomposites is based on the conjugated Ag nanoparticles and Fe3O4nanoparticles. The influences of surfactant, ration of Ag and Fe ions, and the molar ratio of hydrazine hydrate in the reaction were studied. The two-photon fluorescent microscopy images and the MRI data demonstrate that these Ag-Fe3O4nanocomposites can be used for optic marker and T2-weighted magnetic resonance imaging contrast.4. Stable bracelet-like magnetic nanorings, formed by Ag-Fe3O4nanoparticles with average size around40nm, have been successfully prepared in large scale by means of reducing Ag+and Fe3+simultaneously under a mild condition. In the reaction, tiny grains of silver were used as seeds to prompt small Fe3O4nanoparticles growing into a large size, which is essential to enhance the magnetic dipole-dipole interactions, while only superparamagnetic Fe3O4nanoparticles (sized about10nm) can be obtained in the absence of Ag seeds. The XRD, TEM, SAED and the EDS line scan data reveal that these nanoparticles form core-shell structures. These magnetic Ag-Fe3O4nanoparticles assembled into nanorings by magnetic dipole-dipole interactions with a diameter of100-200nm. The saturation magnetization of the nanorings is39.5emu g-1at room temperature. The MRI images indicate that this kind of nanorings have the potential application for diagnostic as a T2MRI contrast agent.