The Synthesis And Multimodality Bioimaging Of UCNPs With Core-shell Structure

Upconversion nanoparticles(UCNPs) possess good application prospect in the field of bio- imaging because of their unique luminescent properties, they also can be used as drug carrier target to nidus for treatment and monitoring. Besides of UCL imaging, UCNPs can also be used as contrast agents in other imaging techniques, such as CT, MRI and etc. However, many shortages limit their usage such as low tissue penetration, lower luminescent efficiency. How to prepare multimodal biological imaging probe with high penetration depth, high luminescent efficiency, good dispersibility, controllable morphology and size has become the key problem. So, my dissertation focused on these two aspects:(1) Ultrasmall Tm3+ and Er3+ doped NaYbF4 nanocrystals with uniform morphology, size and good dispersibility were synthesized by thermal decomposition method in the OA/ODE/OM reaction system, and then Gd3+ indtroduced to form Tm3+ and Er3+ doped NaYbF4@NaGdF4 core-shell nanostructure. TEM, HRTEM and XRD were used to characterize the morphology, size and crystal structure of the as-synthesized nanoparticles. The core-shell structure was confirmed by Mapping through field emission high resolution transmission electron microscopy. Under the excitation of 980 nm laser, intense upconversion emission in 808 nm and relatively weaker emission in red and blue emission ba nd can be observed in NaYbF4:Tm nanocrystals and NaYbF4 :Tm@NaGdF4 nanoparticles. For human eyes are sensitive to blue light, only blue UC L emission was visible when these UCNPs were dispersed in solution, however, the upconversion emission of NaYbF4 :Er and NaYbF4:Er@NaGdF4 nanoparticles in solution presents ora nge under the excitation of 980 nm laser.(2) In order to achieve better dispersion of UCNPs in water, citric acid was used as a surface ligand to replace OA ligand on the surface of NaYbF4 :Tm@NaGdF4 nanocrystals. Hydrophilic nanoparticles were characterized by means of FTIR, TGA, DLS and Zeta potential. MTT test and the H&E staining experiments have proved these UCNPs have no toxicity for cells and biological tissues. When Cit-NaYbF4:Tm@NaGdF4 nanocrystals were injected intravenously into a mouse, significant UC L emission was observed from the liver and spleen after 15 min, whereas the other organs showed no UCL signals, indicating that the Cit-NaYbF4:Tm@NaGdF4 nanocrystals were mainly distributed in the liver and spleen. Another, NaYbF4 :Er@NaGdF4 nanocrystals without citrate ligand was mainly distributed in the liver and subcutaneous tissue, no UC L emission can be observed from spleen. Experimental results show the multifunction nanocrystals can not only be used as UC L imaging probe in cells and small animals, also be used as CT and MRI imaging contrast agent, which have achieved the success in UC L/C T/MRI multimodalitybioimaging.