Surface Enhancement Spectral Effects Of Gold Nanorods And Their Core-shell Structures

When the interaction of the light field and nanoscale metal substrate, the metal nanosubstrate forming a surface plasmon can change the distribution of local electromagnetic field in its vicinity, thus effectively control the optical signal behavior of molecules in its vicinity, which is raised great active and important topic by researchers. Up to now, the surface enhanced spectroscopy technique is basing on the surface plasmon that has been widely used in biological imaging, high sensitivity biological testing.In order to improve the intensity of fluorescence and Raman, silica coating gold-silver core-shell nanorods is employed as enhancement substrates, the influence of spectral correlation between localized surface plasmon resonance of hybrid nanorods and the excitation wavelength and the fluorescence emission wavelength is investigated in this thesis. The results show that the emission intensity of fluorescence molecule is enhanced, when the localized surface plasmon resonance of hybrid nanorods is matched with the excitation wavelength and the fluorescence emission wavelength. At the same time, the silica layer impacting surface enhanced fluorescence is studied. Also, a preliminary attempt to enhance Raman intensity of crystal violet molecule by using gold, gold-silver, gold-silver-silica nanorods as enhanced nanosubstrates is conducted in current thesis. The experimental results show that the three kinds of nanorods perform different Raman enhancement property. The main contents are summarized as follows:1. Gold nanorods sol is prepared via a seed mediated growth method. The gold nanorods aspect ratio is controlled by varying the amount of reagents. Then, gold-silver nanorods are synthesized through chemical reduction. The gold-silver-silica-core-shell-shell nanorods are obtained by using this paper to explore a unique method.2. The affect of gold-silver-silica-core-shell-shell nanorods with have same thickness of SiO2 but different localized surface plasmon to oxazine725 molecular fluorescence intensity is studied by laser spectroscopic technique. The experimental results show that the localized surface plasmon resonance of hybrid nanorods is matched with the excitation wavelength and fluorescence emission wavelength, which can enhance fluorescence intensity. And, as the concentration of substrate increased, the fluorescence intensity showed a trend of decrease after the first increase, which can be explained by the competition between increasing radiative decay and absorbing fluorescence by substrate. Through further analyzing the influence of different substrate on the fluorescence intensity under the same conditions, the coupling degree of localized surface plasmon resonance and emission wavelength of fluorescent molecules is significantly affected by the concentration of the hybrid nanorods. When there is a low concentration of the substrate, the best coupled of the nanorods eventually gets largest enhanced fluorescence molecular emission intensity. When the concentration of substrate increases to a certain amount, there is a significant absorption of fluorescence by the hybrid nanorods which have the largest coupled degree. In the most suitable substrate concentration, the influence of hybrid nanorods with different silica layer and fluorescence enhancement is investigated. The experimental observation shows that the silica thickness (?10 nm) of hybrid nanorods gets the best surface enhanced fluorescence.3. Surface enhanced Raman scattering of crystal violet molecule with gold, gold-silver and gold-silver-silica-core-shell-shell nanorods is investigated. The experimental results that the Raman enhancement of crystal violet can be increased by the coupling localized surface plasmon resonance of nanorods with the excitation wavelength. Comparing with gold nanorods and gold-silver-silica-core-shell-shell nanorods, gold-silver nanorods gets the best Raman intensity, which can be explained by electron ligand interaction of nanorods and localized electromagnetic field. Because long-range electromagnetic enhancement effect is stronger in less than 5 nm, the ability to enhance the Raman signal molecules on the nanorods is weaker with the silica shell thickness increases. The results show that the gold-silver-silica-core-shell-shell nanorods exhibits good SERS activity when the silica thickness of about 5 nm.