Surface Plasmons Induced Fluorescence Enhancement And Photothermal Effect

Due to the unique surface plasmons resonance (SPR) properties, nano-metal materials have been widely studied for a variety of potential applications, ranging from materials science, biomedicine to optoelectronics. Especially, surface plasmon enhanced fluorescence has attracted considerable attention at present. Although the research on SPR has made great progress, there are still some challenges, such as facile process, morphology controllability, high efficiency and industry application. In this paper, we mainly studied the fluorescence enhancement mechanism and the influencing factor on the enhancement performance, such as the metal particles size, shape, etc. The SPR effect was then used to enhance the emission of LED chip. In addition, we investigated the photothermal efficacy of Au nanocages, which were acted as photothermal transducers for cancer treatment.The main works and conclusions are as following:In chapter1, we provide an overview on metal surface plasmons (SP), including the basic properties of SP, the development and applications of SPR enhancement effect.In chapter2, the basic properties of semiconductor quantum dots (QDs) were firstly summarized. Because of their unique properties, such as high photoluminescence (PL) efficiencies, strong brightness and size-dependent PL wavelengths, semiconductor QDs have been extensively studied in biomedicine and photoelectric fields. Semiconductor QDs with different emission wavelengths have been synthesized based on the size effect, including visible emitted CdSe QDs, visible-near infrared emitted CdTeSe and CdTeS alloyed QDs. By improving the synthesis apparatus and controlling the reaction time and the precursor composition, high quality QDs with controllable emission wavelength were prepared. Water-soluble CdTeS QDs were then used in the bio-imaging for breast cancer cells.In chapter3, we mainly studied the resonant PL enhancement effect in the metal-semiconductor QDs composite system. Ag and Au nanoparticles films were prepared respectively by a simple electrostatic self-assemble technique. The SPR absorption properties were controlled by changing the reactant concentration and the following annealing temperature.The PL enhancement mechanisms in the metal/CdSe QDs composite system were also discussed. Due to the annealing treatment, worm-like metal nanoparticles were formed, which induced a highest PL enhancement of11times for the upper CdSe QDs. In addition, a convenient and efficient electrolysis method for preparation of Ag nanoparticles films on the transparent conductive substrates was designed. The electrolysis-Ag enhancement effect on CdSe QDs emission was also investigated.In chapter4, based on the above work, the SP enhancement effect was expanded to the light emitting diodes (LED). Ag nano-film was deposited on the top of GaN-based blue LED by using a radiofrequency magnetron sputtering system. By varying the Ag film thickness and the annealing temperature, a highest PL enhancement of11times for LED was achieved. Metal enhancement of micro-phosphors (which can be used on top of LED) emission was also investigated. Metal nanostructures were coupled with micro-scaled Sr2Si5N8:Eu2+phosphors. By controlling the particles size, shape and inter distance, a brightness PL enhancement by about6times was observed in the metal/phosphors composite film.In chapter5, we studied the photothermal effect of Au nanoparticles due to the SPR properties. The Au nanocages were prepared via a galvanic replacement reaction. The SPR absorption wavelength can be turned from visible to near-infrared range by varying the reaction parameter. Au nanocages with the SPR peak at around800nm were selected as a photothermal therapeutic agent for breast cancer cells or lung cancer cells. We found that the Au nanocages could effectively damage the cancer cells when illuminated by a near-infrared laser with light wavelengths centered at808nm.Highlights of the dissertation are as following:1. High-quality alloyed CdTeSe QDs were synthesized in vacuum condition by a modified method. This vacuum method proved to be of good repeatability and high quantum yields. CdTeS QDs were synthesized in water solution by a much more convenient one-step hydrothermal method. The emission wavelengths of the QDs can be turned from visible to near-infrared range by varying the reaction time. The bio-imaging of cancer cells by these QDs was then achieved.2. Worm-like metal nanoparticles were formed by a simple self-assemble method and following annealing treatment. The worm-like metal nanoparticles possess many more hot spots and excite much higher electromagnetic fields than those of spherical nanoparticles, and hence will induce much stronger PL enhancement. Moreover, a novel electrolysis method for preparation of Ag nanoparticles films was designed, which induced a strong PL enhancement for the coupled QDs. This method is facile, convenient, efficient, low-cost, and can be prepared on a large scale. We expect this method can also be extended to other conductive substrates for the potential application in increasing the efficiency of photoelectric devises.3. An11times PL enhancement of GaN chip was achieved due to the SP resonance from Ag nanoparticles. By the controlling of particles size, shape and inter distance, the PL enhancement of micro-scaled phosphors was first realized due to the strong resonant scattering.4. Au nanocages were used as photothermal transducers for the therapy of cancer. This gentle, minimally invasive and efficient photothermal therapy for cancer will face cheerful prospects.