氧化矽奈米複合材料的設計與應用

Abstract

由於有機/無機奈米混成材料(hybrids)具有組成可調及結構多樣化的特性，近年來，已成為學術及工業界均致力發展的材料。而在各式各樣的混成材料之中，尤其受到青睐的材料是具有高度穩定性、生物相容性、低細胞毒性、及易修飾特性的氧化矽材。在此研究中，利用傳統溶膠-凝膠(sol-gel)的合成方法，我們設計並發展出多種嶄新的奈米混成氧化矽材。以下將簡單介紹這些氧化矽材的合成及應用： (1) 利用油包水的微乳液系統，我們發展出以氧化鐵為核心，氧化矽為殼層且表面修飾聚乙二醇官能基的材料。實驗結果顯示，以此材料作為血管顯影劑，並注射入老鼠血管中，有助於提升腦血管在核磁共振造影下的靈敏度。 (2) 利用油包水的微乳液系統，我們發展出以奈米金為核心，氧化矽為殼層的空心球材料。實驗結果顯示，以此材料作為催化劑，有助於進行對-硝基苯酚的還原。同時，反應結束後，材料並無毒化或聚集現象的產生。 (3) 利用水包油的乳液系統，我們發展出以氧化矽殼層同時包覆水滴及油相分子的材料。此極具潛力的材料，將可作為同時傳遞極性及非極性分子的載體。除此之外，提升材料合成過程中所需界面活性劑的濃度，即可合成直徑僅12奈米的超小氧化矽空心球。 (4) 我們利用中孔洞材料作為晶種，進行蛋白質的異質成核實驗。初步結果顯示，晶種的存在，對於所形成的蛋白質晶體形態上有顯著的影響。

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.