Fabrication Of Mesoporous Silica With Core-Shell Structure For Bio-application

This thesis is concerned with the fabrication of several mesoporous silica materials that are especially tailored to accommodate guest molecule encapsulation-transportation process. In this project I have studied the formation mechanism and surface modification on designing the mesoporous silica with different morphologies (e.g. spherical, helix), mesopore structures in order to meet the requirement as host material of several kind biomolecules/drug molecules. Furthermore, I have done the observation on this novel material for several potential applications like: size-selectivity bioseparation, targeted drug-delivery, and biosensor according to their different pore structure. More detailed work for each chapter in this thesis is discussed as follow:In chapter 2, we report a novel synthesis and selective bio-separation of the composite of Fe3O4 magnetic nanocrystals and highly ordered MCM-41 type periodic mesoporous silica nanospheres. Monodisperse superparamagnetic Fe3O4 nanocrystals were synthesized by thermal decomposition of iron stearate in diol in autoclave at low temperature. The synthesized nanocrystals were encapsulated in mesoporous silica nanospheres through the packing and self-assembly of composite nanocrystal-surfactant micelles and surfactant-silica complex. Different from previous studies, the produced magnetic silica nanospheres (MSNs) possess not only uniform nanosize (90~140 nm) but also a highly ordered mesostructure. Binary adsorption and desorption of proteins cytochrome c (cyt c) and bovine serum albumin (BSA) demonstrate that MSNs are an effective and highly selective adsorbent for proteins with different molecular sizes.In chapter 3, we report a novel one-step synthetic pathway that controls both functionalities and morphology of functionalized periodic helical mesostructured silicas by the co-condensation of tetraethoxysilane (TEOS) and hydrophobic organoalkoxysilane using achiral surfactants as templates. Different from previous methods, the hydrophobic interaction between hydrophobic functional groups and the surfactant as well as the intercalation of hydrophobic groups into the micelles are proposed to lead to the formation of helical mesostructures. Our study demonstrates that these hydrophobic interaction and intercalation can promote the production of long cylindrical micelles, and that the formation of helical rod-like morphology is attributed to the spiral transformation from bundles of hexagonally-arrayed and straight rod-like composite micelles due to the reduction in surface free energy. Furthermore, the helical mesostructured silicas were employed as drug carriers for the release study of model drug, aspirin, and our results show that the drug release rate can be controlled by the morphology and helicity of the materials.In chapter 4, we report a one step synthesis of magnetic helical mesostructured silica (MHMS) rod by self-assembly of an achiral surfactant, magnetic nanocrystals with stearic acid ligands and silicate. This core-shell structured material consists of a Fe3O4 superparamagnetic nanocrystal core and a highly ordered periodic helical mesoporous silica shell. Furthermore, the drug release process is demonstrated using aspirin as a drug model and MHMS as a drug carrier in a sodium phosphate buffer solution.In chapter 5, Dimethyl sulfoxide reductase (DMSOR) was immobilized into carbon nanotubes, which was cast onto the surface of GC electrode, and used as the working electrode (DMSOR-CNT/GC electrode). The results indicated that the electron transfer between DMSOR and GC electrode promoted by carbon nanotubes can be easily performed through their surface-controlled process; they have potential application as DMSO biosensor.In chapter 6, we reported a synthesis of carbon nanotubes (CNTs)/mesostructured silica core-shell nanowires with a carbon nanotube core and controllable highly ordered periodic mesoporous silica shell via the interfacial surfactant template. The results indicate that the core-shell nanowires have highly ordered periodic mesoporous silica shell (space group p6mm), high BET surface area and narrow pore size distribution. The core-shell nanowires have promising applications in biosensors, nanoprobes, and energy storage due to their high surface area, high loading amount of enzyme and good disperse ability in polar solvents. When the core-shell nanowires immobilized with DMSOR was cast onto the surface of electrode, this can be functioned as the working electrode. The results indicated that the electron transfer between DMSOR and GC electrode promoted by core-shell nanowires and the electrode have potential application as DMSO biosensor.