Fabrication And Application Of Low Valence Nanostructures

The ability to design and assemble three-dimensional structures from colloidal particles is limited by the absence of specific directional bonds. As a result, complex or low-coordination structures, common in atomic and molecular systems, are rare in the colloidal domain. It remains a huge challenge. Here, we prepared a "colloidal molecule" via the surface controlled nucleation and growth based on a spherical core-shell nanostructure. Integrated into the idea of Janus structure preparation, the nanocluster was etched controllably and modified with biological molecules locally and asymmetrically using of the spatial orientation of the satellite particles. Therefore, the cluster structure was given a specific direction and a precise chemical link capacity. A larger size of the assembly with the modified cluster can be achieved, the behavior of the assembly process can be studied and a novel function of the new nanomaterials can be researched further.In this thesis, Chapter I delivered the basic knowledge of "nano", nanostructure and the importance of the nanostructure’s further assembly. Concerning on the different assembled structural unit (building block), the spherical core-shell nanostructure, the Janus nanostructure and the specific nanocluster were introduced detailedly, especially on the different preparation methods. The mechanism of formation of the spherical core-shell nanostructure was introduced as well, as a representative.In the Chapter II, the detailed preparation method and process of the composite low-valence nanoclusters Au@SiO2&PS were introduced and discussed. It was comprised of the five parts below:the preparation of gold nanoparticles (Au NPs), the fabrication of gold-silica core-shell nanostructures (Au@SiO2), the surface modification of Au@SiCO2, the fabrication of gold-silica-polystyrene composite low-valence nanoclusters (Au@SiO2&PS) and the purification of Au@SiO2&PS. We fabricated different size of Au@SiO2based on the different size Au NPs prepared. The different silica shell thickness of2to4nm and10to50nm can be achieved via the hydrolyzation of sodium silicate and tetraethoxysilane as the precursor, respectively. The modification of Au@SiO2was conducted with a small comonomer, which has the double bond at one end of the molecule structure, as to connect PS NPs with the surface of the silica shell. By the emulsion polymerization, certain number of PS NPs grew in situ on the modified surface of Au@SiO2and meanwhile, target shape low-valence composite nanoclusters Au@SiO2&n PS were obtained, wherein’n’ means the number of valence and it mainly depended on the relative size of Au@SiC>2and PS NPs. The product obtained usually contains the mixture of nanoclusters with different valence, not only the target one, and some homogeneous PS NPs that did not connect with the core-shell structures. Thereby, a further purification of Au@SiO2&PS, the sucrose gradient centrifugation method, was applied to separate and enrich the target shape Au@SiO2&PS structure.In the Chapter III, some performance and application research was carried out on the nanomaterials obtained in the course of fabrication of low-valence nanoclusters. First, the stability of Au@SiO2nanostructures and their application in the field of laser desorption/ionization time of flight mass spectrometry (LDI-TOF-MS) as energy transfer material was discussed detailedly. The effect of the laser intensity, gold core size and silica shell thickness on the mass spectrometry signals was studied systematically with dPEG6as the model molecule. And the technique was further tested with some small functional molecules, polymers and peptide. Compared with common MALDI-TOF-MS, the sensitivity of our method on small molecules and polymers were much better. Yet, for larger polymers and biomolecules, it needs to be further improved. Second, we designed and explored the self-assembly of Au@SiO2&PS. Controlled etching is conducted at the silica shell that without connection with PS NPs in order to gain the localized bare gold core. With two different etching mechanisms were found, the target gets difficult as the silica shell that connects gold core with PS NPs was etched simultaneously. That’s not we expected. So the revised design with the silica shell increasing based on the whole composite nanoclusters is studied. We got the target shape structures like’nose’after the reaction with treatment of centrifugation and ultrasonic washing.The revised design that using of the thickness difference of silica shell at different locations of the’nose’structure, makes the controlled etching available again. It’s the location with PS NPs and without PS NPs of composite nanocluster originally makes the difference. Adjust the process of etching to gain the bare gold core at the location with less silica and then modify the DNA molecules and achieve the last self-assembly eventually. In this way, the satellite particles create the space oriention originally and pass it on until the final realization of the assembly. It brings the new research interest in novel functional nanomaterials.