The Preparation Of Rare Earth Doped Upconversion Nanoparticles And The Study Of Luminescence Resonance Energy Transfer With Dyes

The rare earth doped upconversion nanoparticles?UCNPs?have unique anti-Stokes luminescence propertiy compared with traditional down conversion materials,and it can be excited by near-infrared light to emit ultraviolet light,visible light,etc.Because of its advantages such as good chemical stability and photostabilization,sharp emission,low cytotoxicity without autofluorescence etc,UCNPs have attracted more attention to research for nanomaterial biological applications including biological imaging,biological detection,drug delivery and photodynamic therapy,etc.Luminescence resonance energy transfer?LRET?is a non-radiative process that the energy transfers to receptor from donor,then the receptor releases the energy by fluorescence emission or other non-radiative methods.Therefore,UCNPs can be widely used for biomedicine application with the designed LRET process according to its unique luminescence property.In this paper,we explored the synthesis method and luminescence properties of Tm-doped UCNPs,and studied the LRET process between UCNPs and tetramethylrhodamine?TAMRA?,and indocyanine green?ICG?,respectively.In Chapter 1,Tm-doped UCNPs?NaYF₄:Yb,Tm?were synthesized,and it can be found that the resulted UCNPs can emit ultraviolet light,visible light and near-infrared light with the excitation of near-infrared light at 980 nm.So the changes of luminescence spectra of Tm-doped UCNPs were explored by changing the Tm/Yb molar ratio.And we found that the luminescence spectra of the UCNPs could be adjusted by changing the doping ratio of Tm/Yb and the relative intensities of the ultraviolet light,blue light and near infrared light changed significantly.Therefore,Tm doped UCNPs with different fluorescence spectra can be synthesized as requirement for better biological applications.The core-shell structure UCNPs was also synthesized and the effect of shell thickness on the luminescence spectra was explored.The result shows that when the molar ratio of core-shell is 1:0.8,the luminescence intensity at 807 nm of core-shell structure UCNPs increases 2³ times indeed.When the core-shell UCNPs are used as near-infrared luminescence probes for biological detection,the higher near-infrared luminescence signal is beneficial to increase detection sensitivity.In Chapter 2,we explored the binding of carboxy modified DNA?A30-COOH?and three different UCNPs?NaYF₄:Yb,Er?modified with different ligands,and the binding condition of A30-COOH to UCNPs was optimized.Here,we first time used A30-COOH to modify BF₄^--UCNPs.Then we constructed a new LRET model by using hybridization reaction between A30-UCNPs and Tetramethylrhodamine modified DNA?T30-TAMRA?.We studied the LRET between NaYF₄:Yb,Er and TAMRA with the UCNPs as donor and TAMRA as receptor.Based on the effect of different concentrations of T30-TAMRA on the LRET of UCNPs-TAMRA system,the sensitivity of the UCNPs-TAMRA system was investigated.The result shows that the system has the feasibility and great application prospects for trace detection of DNA and other biological macromolecules.In Chapter 3,Neodymium?Nd?-doped UCNPs?NaYF₄:Yb,Nd,Er?can be excited by near-infrared light at 808 nm and avoid the overheating under the excitation of 980 nm in water.But,Nd-doped UCNPs have relatively low luminescence in water due to the lower luminescence quantum efficiency.So,in order to improve the biological applications,it is necessary to further improve luminescence intensity of Nd-doped UCNPs in water.Due to the large absorption cross section of ICG near 800nm and the greater overlaps between the emission spectrum of ICG and the absorption spectrum of Nd,we studied the luminescence property of ICG-sensitized UCNPs based on the LRET principle by using ICG as an energy donor and Nd-doped UCNPs as energy receptor.The experimental result shows that,the luminescence intensity of ICG-sensitized UCNPs is higher about 3times than that of UCNPs without sensitization of ICG.Finally,through Hela cell imaging,we compared the effect of luminescence imaging of UCNPs before and after sensitization.