| Due to the localized surface plasmon resonance (LSPR), noble metal nanoparticles show distinctive opticalproperties in the visible and near-infrared region, which lead to a great enhancement of the surface local field around the nanoparticles. Rely on this effect, the intensity of fluorescence and raman scattering of the molecule near the nanoparticles will be strongly enhanced. Therefore, the noble metal particles are showing promising applications and essential research value in various hitech fields.Given the importance of the surface enhanced spectroscopy in biomedical optics field, the surface enhanced fluorescence on the silver particles was studied based upon the previous works in our lab. The submicrometer silver particle with rough morphology was chose as the material of substrate. We focused on the distinctive optical properties of the rough silver particles and the resulting changes of the molecule inphotophysical process. The appropriate physical models were established for analyzing the distribution of the surface local field and the mechanism of metal enhanced fluorescence. Using this kind of silver particles, optical localized surface plasmon device were achieved and applied to on-line detection of oil pollution in seawater. Through theoretical simulation and experience, we gathered lots of data to further optimize the structure of the device so that it could be better applied in biomedical field.In this thesis, the research works include the following aspects:1. We prepared the submicrometer silver particles with rough morphology andcharacterized its structure and optical properties. Using these particles, the surface enhanced raman spectroscopy (SERS) was measured and calculated. For analyzing the uniqueoptical properties of the practical particles, the surface local field and the spectrum of extinction, scattering and absorption of rough silver particle model were simulated by finite difference time domain (FDTD) method. 2. The surface enhanced single-and two-photon fluorescence of CPD4was experimentally detected. Through adjusting optical attenuator,we found that change of fluorescence as a function of exciting lightpower and studied the mechanism of surface enhanced fluorescence (SEF). Based on the interaction between molecule and surface local field, the molecular stimulated emission model was established to explain the reason for particle-induced fluorescence lifetime modification. The results were confirmed theoretically and experimentally.3. The optical localized surface plasmon devicewasfabricated by self-assembly method with the rough silver particles. The device was designed as a single-layer structure and the excitation and collection of optical signal through the same microscope objective. Because of the properties of LSPR, multi-wavelengthexcitation and wide-band signal collection will be realized in this device.4. On-line marine oilpollution monitoring system based on SEF technology was set up, whichis composed of three units:optical path unit, signal collecting and processing unit and sample chamber.By introducing the optical localized surface plasmon device, fluorescence and SEF spectrum of trace amount of diesel oil in seawater were measured in this system. In order to determine the standard material for detectingin practice, radiative enhancement of ten polycyclic aromatic hydrocarbons in diesel oil were calculated as well.5. Distribution of surface local field for closely silver particle pairs and chains of silver particles were simulated by FDTD method. On the basis of the interaction between silver particles, we proposed optimization solution and design in order to increase the available enhanced region of the optical localized surface plasmon device.6. According to the CV model and heat conduction theory, solid heat transfer simulation software was accomplished.With this software, the thermal effect of the quartz in machining process with picosecond laser was simulated. The. results explored and analyzedthe feasibility of the ordered optical localized surface plasmon device machining by picosecond laser.The results and conclusion in this thesis are as follows: 1. The submicrometer silver particles with rough morphology could have LSPR and strong enhancement effect in wide-band. Borrowed the concept of secondary waves, the field superposition of surficial structures was proposed to explain the field enhancement in different wavelength. The analysis indicated that the way of interaction between surficial structures is depend on the plasmon resonance mode of the whole particle. The orbital hybridization for free electron motion in metal particles will caused by introducing the surficial structures, which bring about the field superposition can modify the properties of LSPR.It is the interaction and localization of the surficial structures thatplay a significant and positive role in the enhancement of the surface local field.Higher SERS enhancement factor (107) was measured in experiment, which implied that the rough morphologywould make the submicrometer silver particle break the size limit.2. Fluorescence of molecule was enhanced in response to the rough silver particles. By calculating the intensity of spectrum, it could be found that the single-photon fluorescence was enhanced by34times, while45times for the two-photon fluorescence. Experiments showed thatthe intensity of enhanced single-photonfluorescence grew linearly as the excited light power increases. However, when the excited light power exceeded some threshold value,the intensity of single-photonfluorescence would display weak growth and saturation.This phenomenon indicated the enhancement of excited light play a major role in SEF. In the meantime, the coupling between molecule and silver particles could lead the surface plasmon to generate electromagnetic radiation with the same frequency as fluorescence, which enhanced the fluorescence as well. Compared with enhanced single-photon fluorescence,two-photon fluorescence peak had a redshift of10nm.We conjecturedthat the molecular potential energy curve is changed by the strong surface local field.3. Given the radiation field of silver particles caused by the coupling effect, the molecular stimulated emission model was established to analyze the particle-induced fluorescence lifetime modification. Derived the molecular rate equation in stimulated emission, we can find that the radiation field of silver particles will result in the increase of radiative decay rate and the decrease of fluorescence lifetime. The degree of change of radiative decay rate has a direct relationship with the molecule spontaneous fluorescence lifetime and the EF of silver particles. The radiative decay rate is increased with EF of silver particles. The increase of radiative decay rate not only enhances the fluorescence intensity, but also promotes the absorption of molecules.4. The optical localized surface plasmon device was fabricated by self-assembly method with the rough silver particles and used in the on-line marine oil pollution monitoring system. The localized surface plasmon technology made the detection sensitivity of the system improved by an order of magnitude.The simulated radiation enhancement results showed that differentpolycyclic aromatic hydrocarbon had different EF. Therefore, through choosing the appropriate test substances as standardand using different wavelength excitation, SEF spectrum can effectively identify the composition and content of the oil in the ocean.5. The distribution of one dimensional submicrometer silver particles was analyzed and optimized. Based on the intensity and area of surface local field,it could be found that the optical localized surface plasmon device have optimal enhanced effect when the distance between particles is20nm to60nm. |
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