Micelles As "Fluorescence Protector" For Rare Earth Complexes In Microcapsules

Luminescent microcapsules prepared by the LbL self-assembly method based on electrostatic interaction between oppositely charged macromolecules, have potential applications in laser materials, fluorescence immunoassay and multicolor bioassays. We first separately prepared pure spherical CaCO3 microparticles without any organic additives and poly (sodium 4-styrenesulfonate) (PSS) doped spherical CaCO3 microparticles and then applied them for successful construction of luminescent microcapsules by depositing PSS, poly (allylamine hydrochloride) (PAH), and cetyltrimethylammonium bromide (CTAB) micelles enriching the rare earth compound Eu(DBM)3Phen (DBM and Phen are dibenzoylmethane and 1,10-phenanthroline, respectively). After removal of the carbonate cores by disodium ethylenediaminetetraacetic acid (EDTA) or hydrochloric acid, the hollow highly luminescent microcapsules were fabricated successfully. The characterization results indicate their excellent integrity.Luminescent microcapsules with micelles (microcapsule I) and without micelles (microcapsule II) were prepared with pure CaCO3 made of Ca(NO3)2 and Na2CO3 as core. The UV absorption spectra of Eu(DBM)3Phen show the content of rare earth compounds in each microcapsuleⅠis 6 times of each microcapsuleⅡ. Fluorescence spectra show that the fluorescence intensity of Eu(DBM)3Phen in microcapsuleⅠis about 9 times of microcapsuleⅡ. Unexpected fluorescence enhancement is observed, which we name as the "fluorescence protector" effect of cetyltrimethylammonium bromide (CTAB) micelles. Europium complex is enriched in the hydrophobic cores of micelles, which prohibiting nonradiative deactivation from the Eu(Ⅲ) of Eu(DBM)3Phen in micelles to H2O molecules in surrounding and consequently further enhance fluorescence emission. After core removal using EDTA, large numbers of 4-6μm in diameter hollow luminescent microcapsules with intact structures were successfully fabricated. The microcapsules characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM) and fluorescent microscopy (FM) indicate good integrity and stability.The PSS doped CaCO3 particles were prepared by rapid mixing of equal volumes of Ca(NO3)2 and Na2CO3 solutions with PSS as additive. Luminescent microcapsules with and without micelles were separately prepared with PSS doped CaCO3 particle as core. FM images show that the diameter of microcapsule is about 3μm. SEM and TEM images show excellent integrity of microcapsules. The results of UV and fluorescence spectrometry show that the content and fluorescence intensity of Eu(DBM)3Phen in micelles doped microcapsule are 3 and 8 times of microcapsule with the absence of micelles, respectively.The ratios of the content and fluorescence intensity of microcapsules with and without micelles using CaCO3 particle as core are 6 and 9, respectively. The ratios of the content and fluorescence intensity of microcapsules with and without micelles using PSS doped CaCO3 particle as core are 3 and 8, respectively. The PSS polyelectrolyte macromolecules in the CaCO3 microparticles form inner networks, which enables the penetration and homogeneous dispersion of well separated micelles containing rare earth complexes. The reduced aggregation degree of rare earth complexes inhibits non-radiative energy transfer between the rare earth complex molecules. As a result, the fluorescence intensity is more effectively improved. The results show that the "fluorescence protector" effect of CTAB in microcapsules using PSS doped CaCO3 particle as core is better than in microcapsules using CaCO3 particle as core.In summary, microcapsules with the most intense fluorescence emission of rare earth complexes so far were assembled with CTAB micelles, which show the "fluorescence protector" effect. This work will benefit many disciplines including photochemistry, fluorescence immunoassay and luminescent materials.