Based On The Doping Synthesis, Surface Modification And Imaging Application Of NaYF 4 Upconversion Luminescent Nanocrystals

With the development and application of biological.multimodality imaging technology in the biomedical field,new multi-functional nano-imaging agent has been paid more attention to.Recently,the new multi-functional nano-imaging agent mainly includes rare-earth up-conversion luminescence nanocrystalline(UCNP),carbon quantum dots and graphene and so on.With the anti-Stokes optical characteristics,UCNPs can emit visible short wavelength light irradiated by a near infrared laser.Compared with the traditional down-conversion fluorescent materials,such as organic fluorescent dyes,fluorescent proteins,and quantum dots,UCNPs are of monochrome,high and stable luminous intensity,long fluorescence lifetime,high chemical stability and low biological background fluorescence interference ect..In this paper,NaYF4:Yb3+/Er3+ nanocrystals with different doping concentrations of Yb3+ were prepared by.solvothermal method and.characterized by transmission electron microscopy,X-ray powder diffraction and polycrystalline fluorescence emission spectra.The effects of doping concentration of Yb3+ were studied on the morphology,structure and luminescence properties of NaYF4:Yb3+/Er3+ nanocrystals with size distribution from 13 nm to 38 nm.Then,tuning the Yb3+ dopant concentrationin,we study the changes of luminescence properties of NaYF4:Yb3+/Er3+ nanocrystals with the 980 nm and 915 nm near-infrared light excitation.Compared with the excitation at 980 nm,the nanocrystals can obtain multicolour emissions and high pure single-band UC red emission excited at 915 nm.TGA-modified,S-S-modified and PEI-modified NaYF4:Yb3+/Er3+ with different positive and negative surface charges were prepared by ligand exchange and characterized by zeta potential analysis,transmission electron microscopy,thermal gravimetric analysis,infrared spectroscopy,raman spectra and fluorescence emission spectra before and after the surface modification.And then zeta potentials of NaYF4:Yb3+/Er3+@TGA,NaYF4:Yb3+/Er3+@S-S and NaYF4:Yb3+/Er3+@PEI were about 0.149 mV,-28.5 mV and 40 mV at pH 7.0,respectively.Referred to that of PEI-modified NaYF4:Yb3+/Er3+,the cytotoxicity of TGA-modified and S-S-modified UCNPs were measured and evaluated by MTT method.Finally,Co2+-doped UCNPs were synthesized by solvothermal method by doping cobalt chloride,cobalt oleate and cobalt acetate.And then,luminescent Co2+-doped UCNPs were characterized by transmission electron microscopy(TEM),polycrystalline powder X-ray diffraction(XRD)and fluorescence emission spectra.Morphology,structure and luminescence properties of Co2+-doped UCNPs were studied in details by adjusting the ratio of doping Co2+.Simultaneously,the Co2+-doped NaYF4:Yb3+/Er3+@OCMC nanoprobe was.prepared after the surface modification with O-carboxymethyl chitosan,which was of both magnetism and UCL luminescence,and its application was done for MR and UCL imaging of cells.