Au Colloidal Metal Surface Enhanced Fluorescence Effects Research

Surface Enhanced Fluorescence (SEF) is an important branch in the field of Surface Enhanced Spectroscopy (SES). It has been received more and more attentions with development of mechanism research on the Surface-enhanced Raman Scattering and Surface Plasmon Photonics. In the SEF effect, the fluorescence intensity of the fluorephore molecules can be greatly enhanced by introducing the metal surfaces with specific properties and configuration, which finally leads to an increase to the detection sensitivity. Since the molecules presenting SEF effect include organic fluorephore molecules and biological fluorescence molecules, SEF effect not only has geat scientific significance to the the field of surface enhanced spectroscopy, but also has potential applications in the fields of chemistry, biology, medicine, food science and environmental science, etc.The rapid development of nanomaterial science has provided abundant resources for substrate preparation and characterization in the study of SES. Because the systems that produce the SEF effect include the enhancement substrate and the fluorescent molecules in the vicinity of the substrate surface, molecular properties, the properties of substrate and its surface configurations could influence the enhancement effect significantly. In current thesis, the physical mechanism and possible factors influencing the SEF effect are investigated. There are three parts included in the thesis:The first one is focused on the discussion of enhancement mechanisms of SEF at metal surfaces. The second part is about the investigation of SEF effect in the system of gold nanoparticles to acridine orange molecules. The last part is about the fluorescence enhancement of specific surface configuration to rhodamine and acridine orange molecules.Part one: the enhancement mechanisms of SEF.Various enhancement modles have been proposed for understanding and explaining the enhancement mechanismes of the observed experimental phenomena in the study of SEF effects. In this part, the specific physical processes and correlations between proposed models, which include local field enhancement theory, energy transition effect, and the radiative decay engineering theory, are analyzed and discussed. The relationship between the surface plasmons(SP) and these models are explored, and the effects of the distance between the surface and fluorescence molecules are especially discussed too. Part two:SEF effect of gold nanoparticles to acridine orange moleculesWe use the colloid Au nanoparticles as the substrate and successfully gained a very good fluorescence enhancement for acridine orange molecules in the aqueous system. The possible factors which influence the SEF effect such as the distance between molecules and surface,the distribution of Au nanoparticles and the wavelength of the excition light, are studied experimentally. The results show that properly controlling of the distances between neighbored Au NPs and between AO molecule and Au surface are very important for obtaining an optimized fluorescence enhancement. It is also found that proper excitation wavelength, which corresponds to greater SPR absorption of metal substrate, is another factor that can significantly influence the SEF effect. Since gold nanoparticles are safe for the life bodies, and acridine orange (AO) is widely used for both DNA and RNA detection as a fluorescence chromophore marker, therefore the results obtained from this part could also provide valuable experimental data for the applications of SEF effects.Part there:Fluorescence enhancement of metal substrate surfaces to rhodamine and acridine orange.Two different experimental setups have been designed in the study of SEF effects. One is the solid environment and another is liquid environment. Employing the mechanically polished metallic surfaces including Ag, Al and Cu as enhancement surfaces, we studied the surface enhanced fluorescence effects for Rh6G and acridine orange (AO) fluorophore with laser spectroscopic technique. The results show that strong fluorescence enhancements were observed for Rh6G and AO molecules at Ag and Al surfaces but no obvious enhancement was detected at Cu surface. We discussed the experimental phenomena with local field enhancement theory, which showed that the enhancement effect of SEF is not only dependent on the dielectric properties of the metals but also on the surface morphology of metallic substrates.