Acridine Orange Molecules In The System Of Silver Nanoparticles Surface-enhanced Fluorescence Effect

Surface Enhanced Fluorescence (SEF) is an important new branch in the field of Surface Enhanced Spectroscopy (SES) and a new field developed rapidly in recent years. More and more researchers begin to attention the study of Surface Enhanced Fluorescence effect, many works have been done and a large amount of achievements have been obtained in the theoretical and experimental studies. The property of metal nanoparticles can be known by studying the SEF effect. SEF become a very useful tool with widely application of fluorescence technique in the biotechnology. Hence, the study of SEF can lay the groundwork for developing new detection technology.In the study of surface enhanced fluorescence, the preparation and selection of the substrate is very important. With the rapid development of nano-material science, abundant resources for substrate preparation and characterization in the study of SES have been provided. In the thesis, we use Ag nanoparticles as a substrate to investigate the surfaced enhanced fluorescence effects of acridine orange (AO) molecules, and theoretical analysis has been made. The physical mechanism and possible factors influencing the SEF effect are investigated. There are two parts included in the thesis:The first one studied the fluorescence enhancement effect of silver colloids to AO molecules. The second part deals with the fluorescence enhancement effect of PATP modified silver colloids to AO molecules.The first partThe fluorescence enhancement effect of silver colloid to acridine orange moleculesWe synthesized silver colloids with chemical reduction method, and studied the fluorescence enhancement phenomena of silver colloids to AO molecule using laser spectroscopy. The influence of the particle distribution and the diameter of Ag nanoparticles are investigated experimentally. The results show that properly controlling of the distances between neighbord Ag NPs is very important for obtaining an optimized fluorescence enhancement. Besides, based on Mie theory, when the size of Ag NPs is smaller than the wavelength of emission light, the SEF became stronger with an increase of particle size. In this study, we verified this theoretical viewpoint through experiment.The second partThe fluorescence enhancement effect of PATP modified silver colloids to acridine orange moleculesTo demonstrate the influence of the distance between fluorophore molecule and metal surface on the fluorescence enhancement effect, we have adjusted the concentration of AO molecules and introducing 4-Aminothiophenol molecules as a spacer during the modification of Ag NPs to control the distance between AO molecules and Ag NPs. The result shows that, with the increase of the concentration of fluorophore molecules and PATP molecules, the fluorescence enhancement factor first goes up to a maximum, then followed by a decrease. We discussed the experimental phenomena with local field enhancement theory, which showed the relationship between enhancement factor of AO molecules and the distance between AO molecules and metal substrate. A small separation may result in a fluorescence quenching, but a too long distance also could result in a weaker enhancement. There exists an optimal distance between the fluorophore molecule and metal surface for the best SEF effect.