Design,synthesis And Biological Applications Of Nano-multifunctional Magnetic Resonance Contrast Agents

In order to address two issue in MR imaging: the complex-based agents due to a relatively short increase the imaging time and the single functional agents have some localizations for the diagnoses of diseases or tumors. This thesis is focused on two aspects: 1) the new multifunctional nanoparticle-based agents are designed and synthesized for increasing residence time in cancer cells or tumor; 2) and the formed nano-multifunctional MR imaging agents are applied to targeting and multimodal imaging of biological systems, for improve diagnostic accuracy of cancer cells or tumor.1. Synthesis and biological applications of RBITC-labeled manganese oxide NPs as T₁-weighted MR and fluorescence imaging agentIn this part, monodisperse silica-coated manganese oxide nanoparticles (NPs) with a diameter of approximately 35 nm were synthesized via a thermal decomposition approach and were aminated through silanization. The amine-functionalized core-shell NPs enabled the covalent conjugation of a fluorescent dye Rhodamine B isothiocyanate (RBITC) and folate (FA) onto their surface. The formed Mn₃O₄@SiO₂(RBITC)-FA core-shell nanocomposites are water-dispersible, stable, and also biocompatible when the Mn concentration is below 50μg/mL as confirmed by cytotoxicity assay. Relaxivity measurements show that the core-shell NPs have a T₁ relaxivity (r₁) of 0.50 mM^-1·s^-1 on the 0.5 T scanner to 0.47 mM^-1·s^-1 on the 3.0 T scanner, suggesting a possibility to use the particles as a T₁ contrast agent. We demonstrate a biocompatible magnetofluorescent T₁ MRI contrast agent for targeted MR and fluorescence imaging of cancer cells based on silica-coated Mn₃O₄ NPs. The in vitro flow cytometry, confocal microscopic imaging, and MR imaging studies show that the Mn₃O₄@SiO₂(RBITC)-FA NPs can specifically target to cancer cells overexpressing FARs by the receptor-mediated delivery pathway within a short-time incubation.2. Synthesis and biological applications of gadolinium-labeled superparamagnetic iron oxide NPs as dual-contrast T₁- and T₂-weighted MR imaging agentIn this part, superparamagnetic silica-coated iron oxide core-shell nanoparticles (Fe₃O₄@SiO₂ NPs) with a diameter of approximately 21 nm were synthesized via a thermal decomposition approach and were aminated through silanization. The amine-functionalized Fe₃O₄@SiO₂ NPs enabled the covalent conjugation of a paramagnetic gadolinium complex (Gd-DTPA, DTPA: diethylenetriamine pentaacetic acid) and an arginine-glycine-aspartic acid (RGD) peptide as a targeting ligand onto their surface. The formed Fe₃O₄@SiO₂(Gd-DTPA)-RGD NPs are water-dispersible, stable, and biocompatible as confirmed by MTT cell viability assay. Relaxivity measurements show that they have a T₁ relaxivity (r₁) of 4.2 mM^-1·s^-1 and T₂ relaxivity (r2) of 17.4 mM^-1·s^-1 at the Gd/Fe molar ratio of 0.3:1, suggesting a possibility to use them as both T₁ positive and T₂ negative contrast agents. In vitro and in vivo MR imaging experiments show that the developed multifunctional Fe₃O₄@SiO₂(Gd-DTPA)-RGD NPs enable targeted dual contrast T₁- and T₂-weighted MR imaging of tumor cells over-expressing high affinityα_vβ₃ integrin in vitro and in vivo. Therefore, the dual contrast T₁- and T₂-weighted targeted magnetic resonance (MR) imaging of tumors could significantly improve the diagnosis accuracy.