Interfacial Self-assembly Method For Ordered Structures Composed Of Au Monodispersed Nanoparticles And Their Electromagnetic Coupling Effect

As there are continuous improvements on the synthesis and fabrication of nanostructures, more and more nanotechnologies have been commercialized in recent years. The ability to successfully translate nanofabrication methods from a laboratory to an industrial setting becomes increasingly important. In comparison with the traditional top-down lithography-based nanofabrication, the bottom-up colloidal self-assembly technology can produce ordered structures with smaller feature dimensions without the need for expensive facilities. Each of the current self-assembly approach has its unique advantages, while also has its disadvantages and limitations. Moreover, it is still a great challenge to achieve a high degree of order of the assembled structures that extends over large areas. Therefore, it is quiet urgent to develop a facile, flexible, low-cost and universal self-assembly method for constructing highly ordered assembly structures with an ultra-large scale. Monodisperse Au nanospheres, which have an ultra-spherical and isotropic structure, are expected to achieve the highly ordered assembly structures. These assembly structures have attracted great interest in the field of catalysis, biosensor, and biomedical applications due to their local surface plasmon resonance property and strong electromagnetic coupling features. Herein, the goal of this thesis is to develop a new method for the synthesis of monodisperse Au nanospheres, and to construct a highly ordered Au nanoparticle monolayer with an ultra-large area (>cm2) and 3D novel plasmonic colloidosomes via the simple interfacial self-assembly method, as well as to study on the electromagnetic coupling effects of the ordered Au nanoparticle arrays and their SERS applications. The results are shown as follow,1. Developed a facile and effective method for the synthesis of monodisperse Au nanospheres with well-controlled size.Au nanocrystals, which synthesize from a solution phase, are usually comprised with sharp corners or edges on their entire surface due to their different facet-index potential and anisotropic growths. To solve this issue, we develop a facile and effective strategy to achieve the synthesis of monodispersed Au nanospheres based on a non-focused laser irradiation-induced shape conversion of the uniform Au octahedral nanoparticle. Ultra-smooth Au nanospheres with high monodispersity can be obtained by simply optimizing the laser fluence and irradiation time. The morphology transformation of Au octahedral nanoparticle under the nanosecond laser irradiation strongly depends on a photo-thermal melting-evaporation process.2. Proposed a surface-capillary gradient-induced self-assembly method for the fabrication of highly ordered Au nanoparticle arrays with an ultra-large scale.Since the self-assembly of Au nanoparticles is often difficult to achieve a high degree of order that extends over large areas, herein, we develop a self-assembly method that is not only simple, reliable and inexpensive, but also versatile and easily compatible with existing nanofabrication. The long-range ordered Au nanoparticle monolayers with an ultra-large scale are floating on the water surface, which can be easily transferred onto derisible substrates. We also found that the formation of densely packed Au monolayer is due to the effect of a created surface capillary gradient along the air/water surface.3. Developed a facile approach for the fabrication of novel plasmonic colloidosomes (PCs) based on a new type of revise emulsion systems for the first time.In biomedicine, the hollow plasmonic vesicles with a micro/nano structure can be loaded with drugs for treating cancers. Thus, such vesicles can achieve a double treatment model that combined medication therapy and photothermal therapy, which are very useful for the early diagnosis and treatment of cancers. Herein, we present a new type of water-1-butanol reverse emulsion systems for the first time, and successfully fabricate a novel 3D plasmonic colloidosomes by using the monodisperse Au nanoparticles as the building blocks. The self-assembly process is driven by the principle of the total interface energy minimum. Unlike conventional emulsion approaches, the formed PCs have an HCP multilayered shell, which is attributed to the dissolution of the water droplets into 1-butanol at an appropriate rate. Moreover, the Au colloidosomes display a stronger plasmonic coupling effect with broadband absorption, and hence have a black color intrinsically, so they are also called ’black gold’. This method is universal and also suitable for different metal nanoparticles. These colloidosomes have important applications in photothermal therapy, biosensors, and drug delivery.4. We also studied the electromagnetic field coupling of the ordered Au arrays and their SERS applications.By using the FDTD method, we also studied the surface plasmon resonance coupling of the Au nanoparticle array, and their electromagnetic field enhancement effects. It has been proved that the ordered Au nanoparticle array shows a high fidelity of ’hot spots’ in the HCP arrangement, which can produce a strong and stable electromagnetic (EM) enhancement. It will provide an important platform for the detection of organic molecules.In conclusion, this thesis will provide an enough experimental date and new ideas for the synthesis and self-assembly technique of the Au nanospheres, and also will expand the combination and compatibility between self-assembly approaches and existing nanofabrication methods.