Aqueous Phase Dye-sensitized NaYF₄:Gd/Yb/Er@NaGd F₄:Yb Nanocrystals And Biological Applications

Dye-sensitized upconversion nanoparticles have attracted extensive attention due to their ability to combine the advantages of rare earth upconversion nanoparticles and organic dyes.Upconversion nanoparticles have low toxicity,high chemical stability,narrow emission band and long fluorescence lifetime.However,due to the narrow band and weak absorption caused by the 4f-4f electron transition of rare earth ions,the upconversion luminescence efficiency of nanoparticles is extremely low.Through the sensitization of organic dyes,the wide and strong absorption of dyes makes up for the weak absorption of rare earth ions,and the energy can be transferred from the dyes to nanoparticles.But the dye-sensitized upconversion nanoparticles also become unstable,prone to photobleaching,and water and oxygen can quench their fluorescence.In this paper,a small size Gd³⁺-based upconversion core-shell nanoparticles were prepared.By adjusting the proportion of amphiphilic molecule and nanoparticles,the types of dyes and the concentration of dyes,the nanoparticles were converted to aqueous phase and were sensitized.After that,the prepared aqueous phase dye-sensitized upconversion nanoparticles were applied for cytotoxicity detection,MR imaging,biological metabolism and biological tissue H&E staining.It is confirmed that the aqueous phase dye sensitized nanoparticles wide have application prospect.Firstly,the hexagonal phase NaYF₄:50%Gd,20%Yb,2%Er@NaGd F₄:40%Yb core-shell nanoparticles with a size of about 8 nm were prepared in this paper.Through the characterization of TEM and Fluorescence spectrum,it was proved that core-shell nanoparticles had good morphology and excellent luminescence.Next,the core-shell nanoparticles were modified to make them water-soluble and the optimal ratio of 1:1was found by adding different proportions of DSPE-PEG.Transmission electron microscopy(TEM),fluorescence spectra at different time and DLS tests proved that the modified upconversion nanoparticles had good kinetic stability and dispersion.Then by adjusting the type of organic solvent,the type of dyes and the concentration of the dyes,the optimal solvent,the optimal dye and optimal concentration were determined to be DMSO,Car-cl and 16?g/mg UCNPs,and the fluorescence was about 422 times greater than that before sensitization.By measuring the fluorescence intensity of 24h discontinuous laser irradiation and 7min continuous laser irradiation,it is proved that the stability of the aqueous phase dye-sensitized nanoparticles is positive.By measuring the fluorescence decays of the dye before and after sensitization,it is proved that the energy transfered from dyes to nanoparticles.Then,the prepared aqueous phase dye-sensitized nanoparticles Car-cl-core@shell-PEG was applied to the He La cytotoxicity test,and it was confirmed that the material is low toxicity.Using paramagnetism of Gd³⁺,in vivo and in vitro MR imaging was performed.In vitro MR imaging results were outstanding,and the longitudinal relaxation rate r₁ reached 7.98mM^–1 s^–1.In vivo MR imaging results were excellent,which proved that the materials could indeed be used as a good MRI contrast agent.According to the content analysis of Gd in the main organs and urine and feces of mice at day 1,3 and 5,the metabolic process of the material in mice could be observed,and the elimination rate of the materials in mice at day 5 was more than 70%.By H&E staining of the biological tissues at day 1,3,and 5,the low toxicity of the aqueous phase dye-sensitized nanoparticles was further verified.