Polyethyleneimine-Mediated Preparation And Functionalization Of Iron Oxide Nanoparticls For Molecular Imaging Applications

With the development of nanoscience and nanotechnology, various magnetic iron oxide nanoparticles (Fe3O4NPs) have been widely used as negative contrast agents for magnetic resonance (MR) imaging. For highly sensitive MR imaging of tumors, it is necessary to develop Fe3O4NPs modified with specific ligand molecules that can direct the targeted delivery of the NPs to the tumor sites. In addition, in order to improve diagnostic accuracy and provide complete diagnostic information, some Fe3O4-based composite NPs have been developed for dual-mode or multi-mode imaging, especially for MR/computed tomography (CT) dual mode imaging.Branched polyethyleneimine (PEI) possesses dense primary amino groups, which enable PEI to be used as a stabilizer to form gold (Au) NPs or Fe3O4NPs. In our previous work, we have successfully synthesized PEI-coated Fe3O4NPs (Fe3O4-PEI NPs) with different diameters through a facile one-pot hydrothermal route. The high density of primary amino groups of PEI not only renders the Fe3O4with good colloidal stability, but also mediates the easy surface modification of Fe3O4NPs with different functional molecules, such as targeting ligands or drugs.In this work, hydrothermally synthesized Fe3O4-PEI NPs were first used as a platform to conjugate fluorescein isothiocyanate (FI) and different targeting ligands (FA or HA) for targeted MR imaging of KB cells overexpressing high-affinity folate receptors or Hela cells overexpressing CD44receptors, respectively. Meanwhile, Fe3O4@Au composite nanoparticles (CNPs) for dual-mode MR/CT imaging application were synthesized via the similar approach in the presence of PEGylated PEI-stabilized Au NPs. The properties of these multifunctional NPs including the morphology, size distribution, zeta potential, hydrodynamic size, hemocompatibility, cytocompatibility, r2relaxivity and X-ray attenuation intensity were characterized by different techniques. What’s more, the targeting specificity of the FA-or HA-targeted Fe3O4NPs both in vitro and in vivo were evaluated by using KB cell lines or Hela cell lines, and their xenografted tumor models, respectively. For Fe3O4@Au CNPs, we evaluated their imaging ability through the MR imaging of mouse liver and CT imaging of rat liver and aorta.In chapter2and3, FA-and HA-targeted multifunctional Fe3O4NPs were developed for in vivo T2MR imaging of tumors, respectively. Our results show that the mean size of this two different targeted Fe3O4NPs is15-16nm. Both of them are water-dispersible, colloidal stable and have excellent r2relaxivity. The results of in vitro cell viability and hemolysis reveal that the particles are quite cytocompatible and hemocompatible in the given concentration range. Furthermore, confocal microscopy and flow cytometry data demonstrate the targeting specificity of the FA-and HA-targeted Fe3O4NPs to KB cells and Hela cells, respectively. In vitro cell MR imaging and in vivo tumor MR imaging experiments using these nanoprobes further demonstrate their targeting ability. The results of biodistribution suggest that the nanoprobes can be gradually eliminated from the body after gathering at the tumor sites for a given time period, hence weakening their toxicity to normal tissues. The formed particles can be potentially used as contrast agents for MR imaging of tumors.In chapter4, the Fe3O4@Au CNPs integrating both Fe3O4and Au components in one particulate system have been easily synthesized through the mediation of PEI. The experimental data show that the formed CNPs are water-soluble, colloidally stable, hemocompatible, cytocompatible, and have relatively high r2relaxivity and good X-ray attenuation intensity. These properties afford their uses as contrast agents for MR imaging of mouse liver and CT imaging of rat liver and aorta. The results of in vivo biodistribution of Fe3O4@Au CNPs suggest that the CNPs can be eliminated from the body successfully, and cause no appreciable toxicity to mice.In summary, we developed a facile approach to generating multifunctional FA-or HA-targeted Fe3O4NPs for in vivo targeted MR imaging of tumors and Fe3O4@Au CNPs for MR/CT dual mode imaging of different tissues and organs. With the unique structural characteristics and versatile conjugation chemistry of PEI that facilitate further functionalization with targeting ligands or drugs, PEI-based water-stable multifunctional Fe3O4NPs or Fe3O4@Au CNPs may provid a unique nanoplatform for targeted MR imaging and/or therapy of different biological systems.