Upconversion Luminescence Of Rare Earth Nanomaterials And Phosphorescent Iridium Complexes Synthesis And Biological Imaging Applications

In order to address two issues in fluorescence imaging:high autofluorescence background and limited light penetration. This thesis is focused on the upconversion luminescence and long lifetimes, synthesizing a series of rare-earth nanoparticles with upconversion luminescence and phosphorescent iridium complexes with-μs lifetimes for targeted imaging in vitro and in vivo.I. Implementation of Upconversion Luminescence In Vivo Imaging System and Rare-Earth Upconversion Nanophosphors for Targeted Imaging of Tumors In Vivo and Toxicity StudiesRare-earth upconversion nanophosphors (UCNPs) exhibit unique luminescence properties such as remarkable light penetration depth and no background fluorescence. Up until now, the broad application of UCNPs in bioimaging suffers a hindrance resulting from the absence of a commercially available system for upconcersion luminescence (UCL) imaging. Therefore, we set up the first high contrast upconversion luminescence in vivo imaging system, and developed the methods of targeted imaging of tumors in vivo using upconversion luminescence imaging protocol. Results indicated that UCL possess unique features in vivo imaging:the remarkable light penetration depth (-600μm) and no background fluorescence.More importantly, based on the high specificity between the ligand and receptor: folic acid (FA) and folic acid receptor (FR), arginine-glycine-aspartic peptide (RGD) peptide andαvβ3 integrin receptor, we synthesized the RGD/FA-labeled UCNPs through the chemical methods, and for the first time developed UCL probes for targeted imaging of tumor in vivo. Results showed that RGD/FA-labeled UCNPs can successfully target imaging of tumors in vivo with a high signal-to-noise ratio (-24).To date, there are only few studies concerning the cytotoxicity of UCNPs. No reports on long-term toxicological studies of UCNPs using animal models. Therefore, we demonstrated the long-term in vivo biodistribution and toxicity studies using polyacrylic acid-coated NaYF4 upconversion nanophosphors (PAA-UCNPs) as near infrared (NIR)-to-near infrared (NIR) luminescence probes. In vivo biodistribution imaging studies indicated that PAA-UCNPs originated predominantly from the liver and spleen and can be excreted from the body of the mice through the intestinal tract in a very slow manner. In vivo toxicity studies results indicated that mice intravenously injected with 15mg/kg of PAA-UCNPs survived for 115 days without any evident (body weight of the mice, histological, hematological and biochemical) toxic effects.Ⅱ. Phosphorescent Iridium(Ⅲ) Complexes for Targeted Imaging of Tumor Cells and Ratiometric Imaging of Intracellular Homocysteine and Cysteine1) Based on the high affinity between the integrinαvβ3 and the amino acid sequence Arg-Gly-Asp (RGD), we synthesized RGD-conjugated phosphorescent iridium complex with red emissions for targeted imaging of integrinαvβ3 expressions. Results showed that this complex can specifically target imaging integrinαvβ3 over expressioned U87MG cells with high sensitivity (2μM) and a rapid response time (-15 min). Furthermore, we designed an organic fluorescence probe for targeted imaging of integrinαvβ3 expressions. Photobleaching experiment established that this probe has higher photostability than acridine orange.2) Thiol-containing amino acids, homocysteine (Hcy) and cysteine (Cys) play many crucial roles in biological systems. Herein, we demonstrated ratiometric phosphorescence imaging of intracellular Hcy and Cys using a cationic iridium(III) complex as a luminescent probe. Importantly, cell imaging experiments demonstrated that the probe can monitor the changes of Hcy/Cys within living cells in a ratiometric mode. When KB cells incubated with iridium complex for 30 min at 37℃showed an emission ratio (I586/I547) of> 1, indicating the reaction of iridium complex with Hcy/Cys. In a competition assay, KB cells were pre-incubated with N-ethylmaleimide (as a thio-reactive compound) at 37℃for 1 h and then incubated with iridium complex at 37℃for 30 min. As a result, the phosphorescence intensity of the green channel increased and that of the red channel decreased, so the ratio (I586/I547) was reduced to< 1.