Synthesis And Application Research Of Magnetic Nanocomposites

The nanocomposites offer an excellent platform for the integration of multifunctional materials. They can integrate different materials with multiple functions into one whole entity. Magnetic nanocomposites are the combination of magnetic nanoparticles and other kinds of particles. Such hybrid nanostructures combine magnetic nanoparticles with other nanocomponents, which exhibit paramagnetism alongside other features such as fluorescence or enhanced optical contrast. These features provide a new platform for biomedical applications including enhanced medical imaging, targeted drug delivery, immunoassay detection, etc. The combination of the unique structural characteristics and multifunctional properties of magnetic nanoparticles will bring new opportunities in the field of nanomedicine. Therefore, the study of magnetic nanocomposites is of great significance. In this dissertation, the fabrication, structure, magnetic properties, optical properties, and biological applications of magnetic-fluorescent nanocomposites, core-shell structured and heterostructured magnetic-gold nanocomposites have been studied systematically. The main research content and innovations are listed as follows:1. Synthesis and physical properties of Fe3O4, CdSe@ZnS and gold nanoparticlesThree kinds of nanocomponents, Fe3O4, CdSe@ZnS and gold nanoparticles, were successfully prepared and studied. The samples were characterized by XRD, TEM, HRTEM, UV-Vis, FL, PPMS and other characterization methods.50nm polyethyleneimine coated Fe3O4nanospheres were prepared via coprecipitation method. The hysteresis curves of Fe3O4nanoparticles show that the particles are paramagnetic at room temperature, while paramagnetic at5K. A series of CdSe@ZnS core-shell quantum dots with different sizes and different colors were synthesized via organic method. The quantum yields were found to be larger than50%. By controlling the reaction conditions, we successfully prepared gold nanoparticles of different sizes, and analyzed their surface plasmon resonance performance.2. Synthesis and application of magnetic-fluorescent nanocompositesCore-shell structured Fe3O4-QDs nanocomposites were prepared utilizing the multifunctional properties of polyethyleneimine. The samples were characterized by XRD, TEM, HRTEM, EDS, UV-Vis, PL, PPMS and other methods.4nm CdSe@ZnS quantum dots were self-assemblied to50nm Fe3O4nanoparticles using polyethylenimine. Meanwhile, the surface properties of the quantum dots were altered from hydrophobic to hydrophilic. The polyethylenimine can also help prevent the aggregation of nanoparticles. Both magnetic and optical properties of the prepared nanocomposites were studied, and it was found that good magnetic and fluorescent properties were retained. The further functionalized nanocomposites were used in cell labelling, and it was proved that the nanocomposites can separate and label cells effectively. Toxicity studies have also been done and showed that the as-prepared magnetic-fluorescent nanocomposites have good biological activity.3. Synthesis and applications of core-shell structured magnetic-gold nanocompositesLarge number of5nm gold nanoparticles was attached to the50nm Fe3O4nanoparticles utilizing polyethylenimine. The-NH2groups in the polyethylenimine were covalently bonded to the gold nanoparticles. The electrostatic interaction between negatively charged citric acid coated gold particles and positively charged polyethylenimine coated Fe3O4nanoparticles enhanced the connection. The as-prepared Fe3O4-Au nanocomposites were applied to the electrochemical and surface-enhanced Raman scattering (SERS) detection methods. Dual-mode method was used to detect carcinoembryonic antigen (CEA). The gold nanoparticles in the nanocomposites provided the biological activities to connect antibody and the Fe3O4 nanoparticles provided the magnetic separation capabilities. Combining the two methods, we have obtained a wider detection range and more accurate detection results.4. Sythesis and application of heterostructured magnetic-gold nanocompositesBesides core-shell structured magnetic-gold nanocomposites, the heterostructured magnetic-gold nanocomposites have attracted much attention as well. Using50nm Fe3O4nanoparticles as seeds, the20nm gold nanoparticles were formed at the liquid-liquid interface in the microemulsion. Finally, the dumbbell-like nanocomposites were successfully synthesized. Due to the synergistic effect of Fe3O4-Au, the reducing ability of H2O2was enhanced. The core-shell structured Fe3O4-Au nanocomposites were applied to the electrochemical immunoassay detection for carcinoembryonic antigen. The electrochemical measurement showed good reproducibility and stability, which offers many potential biological applications in the future.