Surface Gold Nanorods Enhanced Two-photon Excited Fluorescence Effects

Two-photon excited fluorescence (TPEF) process with its higher spatial resolving power to make a wide application in the field of physics, chemistry, biology, medical science and microelectronics technology. However, compared with one-photon excited fluorescence emission, the intensity of two-photon excited fluorescence is lower which severely restricted its application and development. In recent years, the rapid development of Surface Enhanced Spectroscopy (SES) technology provides a new effective way to improve the intensity of two-photon excited fluorescence. Theoretical and experimental studies for SES and Plasmon Resonance Photonics has shown that noble metal nanoparticles are often used as the potential metallic substrate to enhance the two-photon fluorescence because of their SPR effect on fluorescent molecular near their surface. Therefore, surface plasmon and excitation effect of metallic nanostructures can be modulated by controlling their size, morphology and composition which in order to achieve effectively enhancement of TPEF effect.In this thesis, we chose gold nanorods (Au NRs) as the enhancement substrate combine with its controllability of SPR effect studied the enhancement effection of TPEF of the Rhodamine590(Rh590). There are two parts included:the first one studied TPEF enhancement effect of Au NRs to Rh590molecules; and the second one dealt with the TPEF enhancement effect of the different concentrations of Au NRs solutions to Rh590molecules. The main contents are as follows:The first partThe enhancement of TPEF effect of Au NRs to Rh590moleculesWe synthesized Au NRs which appeared with different aspect ratios and well-dispersed in seed-grow method by changing the content of reagent in the preparation process. Then, we studied the TPEF enhancement phenomena of Au NRs to Rh590molecules using laser spectroscopy. In order to analysis the above-mentioned problem, there are three steps experiment which we carried out. The first step:by two-photon excitation of Rh590solutions with different concentrations under the changing wavelength of the excitation light we found that when the excitation wavelength was located in800nm, there was a most stable fluorescence signal. The second step:Au NRs-Rh590system were made by mixing four terms of Au NRs which had different aspect ratios of2.5、4.1、4.4and6.2with Rh590solutions. We found that the nanorods with aspect ratio of4.1which had a longitudinal SPR absorption peak at815nm appeared the best fluorescence enhancement under the excitation wavelength of800nm. The last step:Au NRs-Rh590system was made by mixing Au NRs with aspect ratio of4.1with Rh590solutions. Under the changing excitation wavelength, it can be found that fluorescence enhancement effect were more obvious when the excitation wavelength were located at800nm and820nm. By the experiment results, when the longitudinal SPR peak of Au NRs overlapping with the excitation wavelength, the efficiency of excitation should be improved which result in fluorescence enhancement effect. Meanwhile, the larger overlap between the two, the better enhancement may have.The second partTPEF enhancement effect of the different concentrations of Au NRs solutions to Rh590moleculesAu NRs-Rh590system was made by mixing Au NRs with aspect ratio of4.1with Rh590solutions. Under the excitation wavelength at800nm, it can be found that fluorescence enhancement effect was depended on the different concentrations of Au NRs and the distance between Au NRs with Rh590molecules. There is an optimum enhancement effect when the concentration of Au NRs is6.75*10-6M, and the enhancement factor is reached to11. Last but not least, the intensive distribution of metal nanoparticles leads to a better enhancement.