DAST-based Fluorescence Characteristics Of Ternary Core-shell Structure And Performance Of Biological Probes

As the most common fluorescent materials,organic fluorescent materials have many advantages,such as abundant species,high fluorescence quantum yield,and adjustable luminescence color,thus holding great potential applications in the fields of biomedicine and environmental science.However,traditional fluorescent materials have been generally troubled by fluorescence quenching in the aggregated state,which is also one of the biggest problems in the research of fluorescent materials.Differently,4-N,N-dimethylamino-4’-N’-methyl-stilbazolium tosylate（DAST）,as an important organic pyridine salt,can exhibit strong fluorescence in the aggregate state,namely the characteristics of Aggregation-Induced Emission（AIE）.Meanwhile,DAST molecules have good hydrophilicity and can be combined with biocompatible materials and applied in biological imaging.Accordingly,novel DAST-based core-shell nanoparticles were designed and fabricated,and their photoluminescence properties and potential bioimaging applications were explored in this thesis.The contents of this work mainly contain the following aspects:（1）In-depth study of the optical absorption and emission characteristics of DAST solution.Experimental results revealed that both the absorption and emission spectra of the DAST aqueous solution in the visible light band only present one peak,and the difference between the absorption and emission peaks shows a Stokes shift of DAST as high as 164 nm.Moreover,the peak of the fluorescence spectrum of DAST shows a tendency of red-shift with the increase of the polarity of the solution.In the four different polar solvents of dimethylformamide（DMF）,dichloromethane,ethanol,and water,the emission peak of DAST and the polarity of the solvent show a positive correlation.（2）Supramolecular inclusion technology was adopted to prepare DAST@β-CD,whereβ-Cyclodextrin（β-CD）and DAST are the host molecule and the guest molecule for inclusion,respectively.Moreover,the fluorescence characteristics and fluorescence characteristics of the as-prepared DAST@β-CD were investigated.Results indicated that compared with pure DAST aqueous solution,the fluorescence intensity of DAST@β-CD aqueous solution is enhanced,and the enhancement amplitude shows an upward trend with the increase of the molar ratio ofβ-CD and DAST,and finally achieved 2.5 times enhancement with the ratio of 1:6.In addition,the DAST@β-CD aqueous solution exhibited a blue shift of the emission peak as the fluorescence increased.These characteristics can be attributed to the inhibitory effect ofβ-CD on the charge transfer characteristics within the DAST distortion.Fourier infrared spectra of DAST and DAST@β-CD revealed that the dimethylamino group and the styryl part of a DAST molecule entered the cavity of aβ-CD molecule,confirming the combination of DAST andβ-CD.It is indeed inclusion at the molecular level.（3）DAST@SiO₂ and DAST@β-CD@SiO₂ composite microspheres were successfully prepared by the inverse microemulsion method.Due to the aggregation-induced emission characteristics of DAST,both the fluorescence intensities of these two core-shell microspheres were significantly enhanced.Compared with the pure DAST aqueous solution,the fluorescence of the DAST@β-CD@SiO₂ ternary shell/shell/core?microspheres was enhanced by 38.6 times,and it also showed a longer fluorescence lifetime and a blue shift of the emission peak.Subsequent observation by scanning electron microscope proved the highly regular and uniform morphology of the microspheres,with the particle size distribution concentrated in 70─80nm.（4）Cytotoxicity and in vitro cell imaging of DAST@SiO₂ and DAST@β-CD@SiO₂ composite microspheres were further investigated.Results revealed that DAST@β-CD@SiO₂ ternary shell/shell/core microspheres exhibit much lower cytotoxicity than DAST,and they emit bright and stable fluorescence in cell imaging.This benefits from both the high biocompatibilities ofβ-CD and SiO₂.The results in this work experimentally disclosed great potential applications of DAST in bioimaging.