Synthesis Of Functional Mesoporous Silica Materials And Their Applications In The Biological Field

For the past two decades, the synthesis of mesoporous materials has been widely studied and mesoporous materials with various mesostructures, components, and morphologies have been reported. However, compared to the great development of controllable synthesis, the applications of mesoporous materials are not widely exploited and have become one of the major challenges in the research field of mesostructured materials.Mesoporous silica is one of the earliest and most widely studied mesoporous materials and the structure control and functionalization are relatively convenient. Therefore, it should be easier to develop the applications of mesoporous materials based on mesoporous silica. Mesoporous silica show great potential applications in biological field, due to their large uniform pore size, high surface area, large pore volume, facile surface functionalization, various morphologies, and good biocompatibility. This thesis mainly focuses on the preparation of functionalized mesoporous silica and exploration of their applications in biological field.In chapter 2, a facile one-pot strategy was conducted to prepare core-shell Ag nanoparticle@mesoporous silica nanospheres (Ag@MSN). It has been demonstrated that the formation mechanism is based on a synchronous process, which combines several steps into one, including the reduction of silver nitrate, assembly of surfactant-stabilized silver nanocrystals and silica-surfactant micelles, transfer and aggregation of silver nanocrystals to form silver core in less condensed silica mesostructures. The particle size, pore size, morphology, and core-shell structure can be tuned by controlling the temperature and the concentration of sodium hydroxide, silver nitrate and Brij56. The obtained Ag@MSN nanospheres exhibited good antimicrobial performances. This simple one-pot synchronous route can be extended to the preparation of core-shell nanospheres with other metal cores such as Au.In chapter 3, the core-shell Ag2S@MSN mesoporous silica nanospheres with near-infrared (NIR) photoluminescent property were prepared through a facile one-pot route. The Ag2S@MSN nanospheres have uniform core-shell structures with single monoclinicα-Ag2S nanocrystal core and ordered mesoporous silica shell. The Ag2S@MSN core-shell nanospheres exhibited near-infrared emission at round 1275 nm excited by a 648 nm laser diode, which is more stable compared to the bare Ag2S nanocrystal cores. The NIR emission intensity could be enhanced after hydrothermal treatment with higher crystallinity of the silver sulfide cores. The shell thickness could be tuned by adjusting the amount of silica source. Furthermore, core-shell Ag2S@MSN nanospheres with several small Ag2S nanoparticles in one mesoporous silica shell could also be obtained.In chapter 4, mesoporous silica nanospheres with various particle size (50～200 nm) were synthesized under a room-temperature condition, showing more surface silanol groups compared with those obtained at higher temperatures. The cytotoxicity of MSN (with particle size of～90 nm) was evaluated. The MSN did not show significant cytotoxicity at low dosages (<25μg/mL). Statistical comparisons of cytotoxicity between mesoporous and nonporous silica nanospheres exhibited no significant difference, suggesting that the mesoporous structure would not induce cytotoxicity. The results suggest the relatively good biocompatibility of MSNs at low dosage. The effect of MSN on the development of zebrafish embryos was also investigated. The MSN did not affect the development of 12hpf and 24phf zebrafish embryos, but exhibited tardy hatching and development for the 3hpf embryos, which may be related to the mitochondrial abnormality in neuron of brain.In chapter 5, mesocellular silica foams (MCFs) with ultra large pore size were synthesized, functionalized and applied for the immobilization of methyl-CpG binding domain (MBD) proteins and enrichment of methylated DNA. The large cage-like pore structures of the MCF materials retained after functionalization and immobilization. The immobilized MBD proteins exhibited high binding activity and stability, which may be related to the large confined space of the foam-like interconnected porous structures of MCF materials. The obtained MCF-MBD materials can be used for the enrichment of the methylated DNA from the mixture of methylated and un-methylated DNA fragments, showing relatively high selectivity and capacity.In chapter 6, a summary of the whole thesis is made.