Synthesis And Properties Of Photostable And Bright Fluorescent Silica Nanoparticles

Recently, fluorescence imaging has emerged as one of the most powerful techniques for monitoring biological targets and processes in the context of a living system with high temporal and spatial resolution. As the fluorescence imaging technology develops rapidly, the fluorescent analysis based on fluorescent dyes has become an increasingly important method in the field of life science. Among a wide range of fluorescent dyes, cyanine dyes are favoured by an increasing number of researchers and used in numerous relative regions because of their special molecular structures, large molar absorption coefficient, tunable spectrum, enhanced fluorescence after combination with biomolecules, simple synthesis and purification methods and low biological toxicity etc. However, cyanine dyes also have some disadvantages similar to that of traditional organic dyes, such as bad photo stability and low fluorescent quantum yields. Recently, after the appearance of nanomaterials, a large number of researchers prepared silica fluorescent nanoparticles that can be functionalized easily in the surface and have good biocompatibility and light permeability by encapsulation organic dyes within inorganic nanomaterials in order to deal with those problems about fluorescent dyes used in biological appliance, which gives this kind of technique a promising future.In this thesis, we designed and synthesized three kinds of heptamethine cyanine dyes with large Stokes shift. Then we covalent encapsulated these organic dyes into silica nanoparticles by reverse microemulsion method to obtained fluorescence nanoparticles FSNPs-1, FSNPs-2 and FSNPs-3. After controlling the dosages of each group of chemical agents within the microemulsion system, we find the optimized conditions of preparing silica nanoparticles. Eventually, we got the NIR silica fluorescent nanoparticles which have similar particle size, good dispersibility and low aggregation successfully.The TEM images indicated that the three nanoparticles obtained were well-dispersed and have uniform size approximately around 40 nm with shaped spherical. By the measured of TGA we can find the concentration of dye inside the particles was 65.1mg,41.5 mg and 23.8 mg of dye per lg of FSNPs-1, FSNPs-2 and FSNPs-3. We also measured the leakage experiment of dye by immerging the nanoparticles in water for 15 days, the nanoparticles FSNPs-1, FSNPs-2 and FSNPs-3 remained about 98%,93% and 95% of fluorescent intensity, respectively. Application of nanoparticles in vivo imaging demonstrated that all of three nanoparticles will be uptaken into cells easily and the FSNPs-3 was 10 times brighter than the encapsulated organic dye itself. What's more, a huge enhanced cell photostability of FSNPs-3 was proved by raw264.7 macrophages cells. Cell viability results from the MTT assay further demonstrated the excellent biocompatibility of the FSNPs-3 on raw264.7 cell.