Prepartion And Modification Mechanism Of NaGDF₄:yb³⁺, Er³⁺ Magnetic-fluorescent Nanoparticles

Rare-earth doped NaGdF₄nanoparticles have large potential application for themagnetic-fluorescence bimodal molecular probe in the early diagnosis of cancer andtreatment, due to their outstanding upconversion luminescence and theparamagnetic properties. Unfortunately, there are several serious problems,including obtaintion of pure β phase, controllable size, low upconversion intensity,single emission spectra etc, which are major bottleneck restricting the developmentand application. Moreover, studies on rare-earth doped NaGdF₄nanoparticlesapplied to magnetic-fluorescence bimodal molecular probe have not been reported.In this dissertation, NaGdF₄:Yb³⁺,Er³⁺nanoparticles with controlled phase structureand size have been prepared via modified high temperature thermal decompositionmethod by optimizing reaction condition. Modified methods, such as Li⁺ionsdoping and shell-coating, have been employed to improve the intensity ofupconversion luminescence. The effect of the synthetic technology, modifiedmethod and condition on phase structure, the intensity of upconversionluminescence and magnetic properties as well as dispersibility is investigated toclarify the mechanism. Glioma targeting probe with magnetic-fluorescencebifunctional properties has been built by SiO₂coating and amination modificationas well as Cltx grafting. The effect of multimodality imaging has been studied.NaGdF₄:Yb³⁺,Er³⁺nanoparticles have been prepared in oleylamine by hightemperature thermal decomposition method. The effect of reaction conditions on thephase structure, particle size, upconversion luminescence and magnetic properties isexplored. The experimental results show that enhancing heating rate and reactiontemperature as well as prolong reaction time are favourable for formation of pure βphase structure. Pure β phase nanoparticles are obtained at heating rate of20℃/min,reaction temperature of330℃and reaction time of1.5h. The as-preparednanoparticles with13nm are spherical and display excellent dispersibility in thenonpolar solvent, strong upconversion luminescence and paramagnetic properties atroom temperature.The intensity of upconversion luminescence has been enhanced by codopingLi⁺ions. The effect of Li⁺ion concentration on the phase structure, morphology,dispersibility, upconversion luminescence and magnetic properties ofβ-NaGdF₄:Yb³⁺,Er³⁺nanoparticles is investigated in detail. It is found that the phasestructure and upconversion luminescence properties are changed obviously, whilethe morphology and the dispersibility are almost unchanged by codoping of Li⁺ions.When the concentration of the codoping Li⁺ions is lower than15mol%, the structure of the nanoparticles is pure β phase, When the Li⁺ions concentration is inthe range from15mol%to60mol%, the mixture of α phase and β phase is obtained.Pure α phase is formed when the Li⁺ions concentration is60mol%. With thefurther increase of the Li⁺ions concentration, the mixture of tetragonal LiGdF4andLiF is obtained. The intensity of upconversion emission has been significantlyenhanced by codoping of Li⁺ions. When the concentration of the codoping Li⁺ionsis7mol%, the obviously improvement can be attributed to the lowest localsymmetry of the rare earth caused by lattice distortion due to the substitution of Na+ions by Li⁺ions. It should be note that the intensity of green and red UC emissionsis enhanced by about47and23times. When the concentration of the codoping Li⁺ions is too high, the intensity of upconversion luminescence is weakened due to theformation of excessive non-β phase.NaGdF₄:Yb³⁺,Er³⁺nanoparticles are modified by coating a passive shell ofNaDyF₄and an active shell of the Dy³⁺ions doped NaGdF₄. The effects of passiveand active shell on the luminescence and magnetic properties are investigated. Theexperimental results show that the intensity of upconversion luminescence andmagnetization are both enhanced by the shell, and the paramagnetic charactersremain unchanged. The intensity of green UC emission and magnezation of thenanoparticles are enhanced by about2and1times respectively by the passive shell.By coating active shell NaGdF₄: Dy³⁺, NaGdF₄: Yb³⁺,Er³⁺@NaGdF₄:Dy³⁺nanocomposites possess excellent upconversion （UC） luminescence,downconversion （DC） and paramagnetic characters. The intensities of green and redUC emission and the magnezation of the nanoparticles were enhanced by about7,2times and2times, respectively. The blue and yellow luminescence is also observedunder UV excitation at350nm.NaGdF₄:Yb³⁺,Er³⁺,Li⁺@NaGdF₄:Eu³⁺nanoparticles（MFNPs） are prepared byhigh temperature thermal decomposition method. The as-prepared nanoparticleswith mean size of20nm are uniform spherical and exibits excellent dispersibility inthe nonpolar solvent. These nanoparticles possess excellent upconversionluminescence and downconversion luminescence. The intensity of green and red isenhanced by5times and4times compared to NaGdF₄:Yb³⁺,Er³⁺,Li⁺nanoparticles.In addition, the strong red luminescence is observed under UV excitation at395nm.MFNPs@SiO₂-NH₂multifunctional nanoparticles are prepared by reversemicroemusion method. The as-prepared multifunctional nanoparticles are activatedby glutaraldehyde and then coupled using the Cltx to synthesis magnetic-fluorescence multifunctional gliomas targeting probe. MRI/optical multimodalityimaging in vivo and viro are investigated. The results show that theMFNPs@SiO₂-NH₂nanoparticles with36nm have excellent dispersibility andstablity in water. High-performance upconversion and downcoversion luminescence as well as good paramagnetic properties are simultaneously observed, and the effectof T1weighted image was obviously enhanced. MFNPs@SiO₂-Cltx molecular probehas special affinity to C6gliomas cells and no cytotxieity. The excellent effect ofMRI/optical mutimodal imaging is observed after circulating in vivo for2h.