Rare Earth Upconversion Luminescence Nanomaterials And Their Applications In Biomedical Imaging

Rear-earth upconverting luminescent phosphors(UCPs) have many advantages, such as low toxicity,high chemical stability and optical stability,sharp emission lines, long emission lifetimes;In addition,under continuous-wave(CW) NIR excitation at 980 nm have advantages also,such as deeper light-penetration depth,no photodamage to living organisms and avoid background fluorescence effectively.All these favorable properties have indicated great potential for UCPs be a new kind of biological luminescent labels.A prerequisite for rear-earth upconverting luminescent nanophosphors(UCNPs) biological applications is to gain access to water-soluble nanoparticles bearing appropriate functional groups(such as -COOH,-NH₂ or -SH) on their surface.There are two parts in this thesis.One is the preparation of UCNPs with different morphologies,size and host matrix doped with different exciting ions using modified hydrothermal conditions.Another is the surface modification of UCNPs,surface ligand epoxidation and silica coating strategies have been developed that convert the hydrophobic UCNPs to hydrophilic ones,and the modified UCNPs have been used for bio-imaging.â… .Synthesis of UCNPs and their upconverting luminescent properties1) Hydrothermal Synthesis of Hexagonal Lanthanide-doped LaF₃ Nanoplates with Bright Upconversion LuminescenceWe have synthesized hexagonal Yb/Er and Yb/Ho co-doped LaF₃ nanoplates with uniform morphology and size and bright upconverting luminescence by mild temperature hydrothermal process.The hexagonal nanoplates can be easily dissolved in nonpolar solvents such as chloroform and cyclohexane.Under CW excitation at 980 nm,the Yb³⁺/Er³⁺ and Yb³⁺/Ho³⁺ co-doped LaF₃ nanocrystals emit bright orange (a combination of green and red,1.5 photon absorb process) and green(2.0 photon absorb process)upconversion luminescence,respectively.2) Synthesis of Bright Multicolor Upconverting emission of NaYF₄:Yb,Er Nanocrystals by Changing Crystalgraphic and MorphologyDifferent morphologies of NaYF₄:Yb,Er naoparticles and nano-(micro-)rods have been prepared by changing the ratio of ethanol to water,mount of NaF in our ethanol/water/oleic acid/sodium oleate/NaF reaction systems.Under different experiment conditions,monodisperseα-NaYF₄:Yb,Er naonspheres and nanocubic,β-NaYF₄:Yb,Er nanorod with controlled slenderness ratio(ratio of length to radiometer from 3.25 to21) has been synthesized via a facile hydrothermal route. Mulitcolor upcoverting luminescence can been realized by the different morphologies of NaYF₄:Yb,Er micro-rods,the intensity ratio of green(514～560 nm) to red(635 680 nm) emission(f_g/r) can be tuned from 0.44 to 2.51.3) Shape-Controlled Synthesis and Upcoverting Luminescent Properties of Hexagonal NaYF₄:Yb,Er Nanocrystals With Multi-MorphologiesBased on the second section,by changing the ratio of ethanol to water, concentration of rare-earth ions and temperature in our ethanol/water/oleic acid/sodium oleate/NaF reaction systems,hexagonal snowflake likeβ-NaYF₄:Yb,Er 2D structure with good crystalgraphic have been synthesized via a facile hydrothermal mute.The possible formation mechanisms for the products with various architectures are presented.â…¡.UCNPs' surface modification and for bio-imaging applications1) Facile Epoxidation Strategy for Producing Amphiphilic Up-Converting Rare-Earth Nanophosphors as Biological LabelsHerein,3-chloroperoxybenzoic acid was used to epoxidate the surface oleic acid (OA)ligand to ternary-ring epoxidation compound,and further coupling with polyethylene glycol monomethyl ether(mPEG-OH),which making the hydrophobic UCNPs to amphiphilic ones.The amphiphilic mPEG/UCNPs have good optical and chemical stability at different pH values,and been used as bioimaging probes.2) Multimodal Luminescence Core-shell Nanocomposites for Targeted Imaging of Tumor CellsThe organic dye incorporated silica coated UCNP nanocomposites as synthesized are well dispersed and have a uniform shape and size distribution,water-soluble and biocompatibility.The UCNP@SiO₂(FITC)-NH₂ nanocomposites readily conjugated with folic acid.By use of confocal microscopy and flow cytometry,we demonstrated that the receptor-mediated delivery of FA conjugated nanocomposites targeting FR(+) cancer cells by qualitative bioimaging and quantitative analysis.