Designing and Utilizing Hybrid Silica Nanoparticles

• Main Authors: Si-Han Wu, 吳思翰
• Other Authors: 牟中原
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/27702117174182462346

博士 === 國立臺灣大學 === 化學研究所 === 101 === Hybrid nanoparticles constructed from organic and inorganic components have been attracting increasing interest in both industry and academia due to its structural diversity and compositional flexibility. Among the various hybrids, silica is believed to be one of the most attractive candidates because their physicochemical stability, biocompatibility, low cytotoxicity and easy functionality. In this study, a variety of highly promising silica nanomaterials were designed and synthesized using a conventional sol–gel pathway. The following descriptions summarize the structure, composition, and utilization of these hybrids. (1) A novel MR angiographic method, 3DΔR2-mMRA (three dimensional and ΔR2 based microscopy magnetic resonance angiography), is developed as a clinical diagnosis for depicting the function and structure of cerebral small vessels. However, the visibility of microvasculatures and the precision of cerebral blood volume (CBV) calculation greatly rely on the transverse relaxivity and intravascular half-life of contrast agent, respectively. In this work, we report a blood pool contrast agent named H-Fe3O4@SiO2-PEG where multiple Fe3O4 nanocrystals are encapsulated in a thin silica shell to enhance the T2-relaxivity (r2 = 342.8 mM-1 s-1) and poly(ethylene glycol) (PEG) are employed to reduce opsonization and prolong circulation time of nanoparticles. Utilization of the newly developed H-Fe3O4@SiO2-PEG with a novel MR angiographic methodology, a high-resolution MR image of rat cerebral microvasculatures is successfully obtained. (2) In this work, size-controlled gold nanocatalysts (2.8 to 4.5 nm) inside monodisperse hollow silica nanospheres, Au@HSNs have been prepared by using water-in-oil microemulsion as a template. The size of gold nanocatalysts can be easily controlled based on gold precursor, chloroauric acid concentration used during synthesis. These Au@HSNs nanocatalysts were characterized by transmission electron microscopy, scanning electron microscopy, N2 adsorption-desorption isotherms, powder x-ray diffraction, and UV-vis spectrometer. Furthermore, we demonstrate their catalytic capability to the 4-nitrophenol reduction reaction in the absence and presence of a thiol compound, meso-2,3-dimercaptosuccinic acid. The results show that the Au@HSNs display highly catalytic activity and resistant ability to other strongly adsorbing molecules in reaction solutions. (3) Nanoemulsions with very high stability can be created by ultrasonication using a rich variety of surfactants, oils and solution conditions. Multicompartments within a nanoemulsion droplet can also be created via a carefully chosen surfactant system. We will show in this paper that silica templating of a nanoemulsion system results in compartmentalized hollow silica nanospheres (HSNs) of sub-100 nm size under neutral pH conditions. The system consists of water, cetyltrimethylammonium bromide (CTAB), tetraethyl orthosilicate, n-hexadecane, n-octane and n-hexanol. Two types of HSN can be obtained by manipulating the formulation; one is named single-compartment HSN (SC-HSN), where the HSNs encapsulate a single water-in-oil droplet; the other is multiple-compartment HSN (MC-HSN), where the HSNs encapsulate multiple smaller HSNs. Using a high concentration of CTAB, we obtained a transparent solution of narrow size-distributed ultra-small HSNs (US-HSNs) with a diameter of 12 nm. Parameters involved in the nanoemulsion have been examined and a possible mechanism is proposed. We show further that various new types of nested interior structures within HSNs could be created by using other block co-polymer type surfactants. Changing the oils to various food oils can also lead to biocompatible multi-compartmentalized hollow silica nanospheres. A potential application of SC-HSNs as a co-delivery system of hydrophilic and hydrophobic drugs was demonstrated in simulated body fluid (SBF) using oil-soluble and water-soluble dyes as model compounds. Finally, we consider the mechanism responsible for the rich varieties of the nested structure in HSNs and discuss factors promoting the stability of the nanoemulsion system for easy templating with ultrason-induced sol-gel silica chemistry. (4) Two types of mesoporous materials, called SBA-15 and broken porous silica (designed as BPS), were used as nucleants for heterogeneous nucleation of protein crystals. Preliminary results showed that the effects of nucleants on crystallization, especially which in crystal morphology, were significant.