Synthesis, Properties And Application Of Precious Metal / Mesoporous Silica Core - Shell Composites

The noble metal nanostructured materials possess unique optical, electrical and magnetic properties due to the quantum size-, surface-and volume effect, which have widespread applications on optics, electronics, sensing, catalysis, biology and medicine. For instance, Ag and Au as the most promising plasmonic nanomaterials, have received increasing attention in recent years. Extensive research is ongoing to synthesize the silver and gold nanostructures with different sizes and well-controlled shapes including nanoparticles, spheres, nanowires, nanorods, nanocubes and triangular plates, and further realize the widely used in surface-enhanced Raman scattering (SERS), biological tag, biosensor and cancer therapy owing to the intense surface plasmon resonance (SPR) properties. However, one of the major problems should be addressed is rationally designing the nanocomposites with additional desirable functionalized components and sophisticated structures to endow plasmonic nanostructures with multifunctional and synergistic properties.Core-shell and yolk-shell nanostructures are the new type of multifunctional materials in terms of distributing different compositions with various functionalities spatially on nanoscale. Furthermore, mesoporous silica as one of the most exciting materials has attracted great attentions in recent years because of the tunable pore size, high surface area, large pore volume, easy modified surface, good biocompatibility and outstanding applications on catalysis, adsorption and biology. Therefore, in this thesis, we realize the combination of the advantages of noble metal and mesoporous silica materials base on the synthesis, construction and bioapplications of these multifunctional materials. We also systematic investigate the construction of noble metal@mesoporous silica core-shell and yolk-shell nanostructures, spatially confined galvanic replacement reaction, the SPR properties and biaoapplications on metal-enhanced fluorescence (MEF), SERS, controlled drug release and chemo-photothermal therapy.In chapter2, a novel mesoporous nanocarrier consisting of a silver core, a silica spacer with controlled thickness and a fluorophores-loaded mesoporous silica shell was fabricated for the metal-enhanced fluorescence (MEF) and Forster resonance energy transfer (FRET) effects. The fluorescence enhancement is up to12-,4.8-and9-fold for EiTC, FiTC and Rh B with the silica spacer in the thickness of8nm, respectively. We also demonstrate that the thinner silica spacer thickness (down to3nm) leads to a decrease in the enhancement factor. Moreover, when the EiTC acceptor and FiTC donor are loaded in the mesopore channels, the FRET efficiency can be increased for about2.5times. This Ag@SiO2@mSiO2nanocarrier with large open channels, high surface area and pore volume presents huge potentials as a general nanocarrier for the study of MEF and FRET with numerous fluorophores, the mesopore channels can also simultaneity load other macromolecules, DNA, antibody and drug for multiple applications.In chapter3, the synthesis of Ag@mSiO2yolk-shell nanostructure, the mechanism of spatially confined galvanic replacement reaction and the application on SERS were explored. The core-shell Ag@SiO2@mSiO2was treated in a Na2CO3solution to select etching the dense SiO2middle layer via the protected of hexadecyltrimethylammonium bromide (CTAB) surfactant to prepare the Ag@mSiO2yolk-shell nanostructure. We started with the mesoporous silica coated silver yolk-shell structure after hydrothermal treatment as a template to synthesize the Au-Ag@mSiO2nanocarriers with SPR peak over a broad range from450to790nm by means of spatially confined galvanic replacement reaction. The detailed mechanism of spatially confined galvanic replacement reaction was investigated. Furthermore, the Au-Ag@mSiO2nanocarriers with different SPR peak can efficient adsorb Raman probe molecules of4-ABT and DTTC for SERS. These Au-Ag@mSiO2nanocarriers with tunable SPR properties for SERS application and can be uptaken by HeLa cells through endocytosis for cell label, the mesopore channels can also simultaneity load other fluorophores and drugs for multiple labels, imagings and detections.In chapter4, the mesoporous silica coated Au-Ag nanocages were selected for chemo-photothermal therapy. The mesoporous silica coated silver yolk-shell structure can be used as a template to synthesize the Au-Ag@mSiO2nanocarriers by means of spatially confined galvanic replacement method. The Au-Ag@mSiO2nanocarriers with SPR peak at820nm can effectively absorb and convert NIR light into heat, which can be rapidly dissipated into the surroundings to trigger the release of preloaded drugs in the mesoporous shell. The in vitro studies confirmed that this novel nanocarrier is feasible for remote-controlled drug delivery with NIR light illumination and can realize the synergistic effect of combining chemotherapy and photothermal therapy and much higher than the sum of the independent treatments, which could offer a new method of highly effective drug delivery and caner therapy.In chapter5, the surface grafting of polymer and near-infrared controlled drug release can be realized base on mesoporous silica-coated Au nanocages with smart polymer carrier. Firstly, scalable (0.4g per batch) and size-controlled (30-100nm) Ag nanocubes can be synthesize via a facile solution completely filled reaction container approach. The thickness of the silica coating can be controlled from8to50nm by carefully changing silica precursor concentration to obtain Ag-nanocube@SiO2core-shell structures, and then mesoporous silica is coated around the Ag-nanocube@SiO2nanoparticles by using CTAB as a template. The mesoporous silica coated Au nanocage with tunable SPR peak from500-1300nm is sequentially prepared by means of spatially confined galvanic replacement reaction between yolk-shell Ag-nanocube@mSiO2and HAuCl4aqueous solution (Au-nanocage@mSiO2). Finally, the PNIPAM polymer shell is covalent anchored to the surface of mesoporous silica using atom transfer radical polymerization (ATRP) method. The Au-nanocage@mSiO2@PNIPAM nanocarrier presents good biocompatibility and high DOX loading capacity (23.5wt%). Upon irradiation with NIR laser, Au nanocage can effectively absorb and convert NIR light into heat due to photothermal effect, resulting in the shrinkage of PNIPAM polymer shell covered on the surrounding of mesoporous silica, which can be used to realize the triggered release of entrapped DOX drugs. This nanocarrier can achieve the synergistic chemo-photothermal therapy effect and significantly enhance cancer cell killing. Such a controlled nanocarrier is expected to be widely used in biomedical application and especially for cancer therapy.In chapter6, the whole thesis is summarized.