Preparation And Fluorescence Properties Of PMDA-Si Rare Earth Core-shell （SiO₂@PMDA-Si-RE-L） And Core-shell-shell Composites （SiO₂@PMDA-Si-RE-L@SiO₂） And Interaction With BSA

Inthispaper,2,5-bis（amidopropyltriethoxysilyl）terephthalicacid（HOOC）₂C₆H₂（CONH（CH₂）₃Si（OCH₂CH₃）₃）₂,abbreviatedasbifunctional organosilane of PMDA-Si,was synthesized.In addition,good dispersion silica microspheres were synthesized by classical St?ber method.Due to the abundant active hydroxyl groups on the surface of silica spheres,hydrolysis-condensation reaction can take place with alkoxyl groups of bifunctional organosilanes,and PMDA-Si be covalently grafted onto the surface of silica spheres through self-assembly process.Then,the carboxyl oxygen atoms in PMDA-Si can be coordinated with rare earth ions RE=Sm,Eu,Tb and Dy to prepare four binary core-shellrareearthorganic-inorganicnanostructuredcomposites SiO₂@PMDA-Si-RE.Inaddition,eightternarycore-shellrareearth organic-inorganicnanostructuredcompositesSiO₂@PMDA-Si-RE-Lwere synergistically prepared by adding phen and dipy as the second ligand.Finally,twelve core-shell rare earth organic-inorganic nanostructured composites with silica as core and rare earth organic complexes as shell were obtained.The morphology,structure and luminescent properties of the core-shell rare earth organic-inorganic nanostructured composites were characterized by scanning electron microscopy,transmission electron microscopy,infrared spectroscopy and fluorescence spectrometer.The results of SEM,TEM,EDX and FT-IR analysis show that rare earth organic complexes are successfully coated on the surface of silica spheres.The size of the silica sphere and the thickness of the shell rare earth organic complex are about 180 nm and 10 nm,respectively.The photoluminescence properties of samarium,europium,terbium,dysprosium binary and ternary core-shell organic-inorganic nanostructured composites were studied by fluorescence spectroscopy.The results show that the europium,terbium binary and ternary core-shell organic-inorganic nanostructured composites have strong fluorescence emission intensity and fluorescence lifetime.In the fluorescence emission spectra of europium series core-shell organic-inorganic nanostructured composites,the fluorescence emission intensity of ternary core-shell composite increased by 1.57 and2.88 times compared with binary core-shell composite with the addition of phen and dipy as the second ligand.In the fluorescence emission spectra of terbium series core-shell organic-inorganic nanostructured composites,the fluorescence emission intensity of ternary core-shell composites increased by 1.32 and 2.36 times compared with binary core-shell composites with the addition of phen and dipy as the second ligand.In addition,the triplet energy levels of PMDA-Si are higher than those of excited states of emission fluorescence of samarium,europium,terbium and dysprosium ions.The energy absorbed by organic ligands from the ultraviolet region can be effectively transferred to samarium,europium,terbium and dysprosium ions and sensitized their luminescence.In the three series of phen/dipy ternary core-shell organic-inorganic nanostructured composites of samarium,europium and terbium,the triplet energy levels of the second ligand（phen and dipy）are also higher than the excitable energy levels of emission fluorescence of samarium,europium and terbium ions.The luminescent properties of ternary core-shell organic-inorganic nanostructured composites of samarium,europium and terbium ions are better than those of corresponding binary core-shell nanostructured composites.However,the fluorescence properties of dysprosium ternary core-shell organic-inorganic nanostructured composites are lower than those of corresponding binary core-shell nanostructured composites due to the low matching between dysprosium ions and triplet energy levels of phen and dipy,and the addition of the second ligand can not effectively transfer energy to dysprosium ions.In this paper,a novel core-shell-shell rare earth organic-inorganic nanostructured composites was prepared by sol-gel method,using CTAB as surfactant through the hydrolysis and condensation reaction of tetraethyl orthosilicate.A layer of amorphous silica was uniformly coated on the surface of core-shell rare earth organic-inorganic nanostructured composites.Twelve kinds of core-shell sandwich structure rare earth organic-inorganic nanostructured composites were prepared.The morphology,structure and luminescent properties of core-shell-shell rare earth organic-inorganic nanostructured composites were characterized by means of SEM,TEM,EDX,FT-IR spectroscopy,XRD powder diffraction and fluorescence spectrometer.The results of SEM,TEM,EDX,FT-IR spectroscopy and XRD powder diffraction analysis show that the core-shell rare earth organic-inorganic nanostructured composites surface are uniformly coated with an amorphous silica shell.The size of rare earth organic-inorganic nanostructured composites with core-shell-shell sandwich structure is about 220 nm,and the thickness of the outer coated silica shell is about 10 nm.The photoluminescence properties of samarium,europium,terbium,dysprosium binary and ternary core-shell-shell organic-inorganic nanostructured composites were studied by fluorescence spectroscopy.The results showed that under the protection of amorphous silica shell,rare earth organic complexes were immobilized on inorganic silica matrix as intermediate layer,and the vibration energy loss of ligand molecules could be greatly reduced.The fluorescence emission intensity of samarium,europium,terbium and dysprosium series core-shell-shell organic-inorganic nanostructured composites is significantly higher than that of their corresponding core-shell organic-inorganic nanostructured composites.Similarly,the fluorescence quantum yields of europium binary and ternary core-shell-shell organic-inorganic nanostructured composites are also significantly higher than those of corresponding core-shell organic-inorganic nanostructured composites.In addition,the fluorescence emission spectra of europium and terbium series core-shell-shell organic-inorganic nanostructured composites in aqueous solution were measured.The results show that the introduction of inert SiO₂ shell can protect rare earth luminescent ions from the quenching effect of the surrounding environment.The core-shell-shell rare earth organic-inorganic nanostructured composites maintain good optical stability in aqueous solution.In order to study the interaction between rare earth ions and various physiological active substances,the interaction between europium,terbium core-shell-shell organic-inorganic nanostructured composites and bovine serum albumin（BSA）was further investigated by fluorescence spectroscopy.Fluorescence emission spectra show that europium and terbium core-shell-shell organic-inorganic nanostructuredcompositesinteractwithBSAtoforma SiO₂@PMDA-Si-RE-L@SiO₂-BSA composite,which changes the microenvironment around BSA.However,the shift of characteristic peaks does not appear,indicating that the conformation of tyrosine and tryptophan residues has not changed.This study has far-reaching significance for exploring the biological application of core-shell-shell rare earth organic-inorganic nanostructured composites,and also provides a new method and new ideas for the preparation of new fluorescent probes.