The Application Of Metal Iridium Complex Nanoparticles In Radioluminescence Imaging And Long Phosphorescence Imaging

Metal Iridium complexes have received extensive attention in the biomedical field such as optical imaging and photodynamic therapy due to its excellent light stability,long phosphorescence lifetime,high quantum yield,widely tunable absorption and phosphorescence spectra,as well as unique heavy atomic effects.Since the absorption bands of the Iridium complexes was located in the visible light region?350-500 nm?,they have a poor penetration depth.Until now,most of their applications were limited in vitro due to the poor penetration depth.For the application of Iridium complexes to in vivo optical imaging,many stratedges have been proposed.In recent years,Cherenkov Imaging?CLI?,as a spontaneous optical imaging method for radionuclides,has been widely used in tumor imaging,biodistribution and other researches.However,the emitted light of weak luminescence CLI was mainly located in the blue-violet region.Therefore,it is designed to combine radioisotopes with luminescent nanomaterials,which could use Cherenkov radiation to excite nanomaterials by Cherenkov energy transfer?CRET?and known as radioluminescence?REFI?.The REFI could not only enhance the CLI intensity,but also releaize the tunable emission spectrum depended on the luminescent materials,thereby achieving deeper tissue penetration depth.In addition,afterglow imaging is the other solution which refers to the delayed illumination after removing the excitation source,it could image with a higher signal-to-noise ratio.Based on the research of the Iridium complexes,we explored the REFI properties with ¹⁸F-FDG and long-phosphorescence afterglow imaging in vivo.The specific research work is as follows:For the first part,the metal Iridium complex nanoparticles?Ir@liposome?were prepared by liposome encapsulation method,and their REFI properties were studied by combaing with the medical isotope ¹⁸F-FDG.The optical signal intensity and penetration depth of fluorescence imaging?FMI?,Cerenkov imaging?CLI?,and radioluminescence imaging?REFI?were explored by covering different thickness tissue.The optical signal intensity and the signal ratio of tumor to muscle were also compared in the mouse model.Ir@liposome mixed with endogenous excitation source ¹⁸F-FDG achieved deeper tissue penetration depth and higher signal-to-noise ratio.This method can be widely applied to improve the application of more Iridium complexes in optical imaging.In the second part,we chose three Iridium complexes with the same C^N ligand and different N^N ligands.The N^N ligands were phenanthroline,3,8-dibromophenanthroline with heavy atom and electron withdrawing group,and thiophene phenanthroline with electron donating group,which were studied to compare their long phosphorescent properties.The 3,8-dibromophenanthroline Iridium complexes showed the strongest afterglow phosphorescence intensity and was prepared into water-soluble nanoparticles.Afterglow imaging was performed subcutaneously on the back of the mouse,which showed a higher signal-to-noise ratio than fluorescence imaging.