Surface Plasmon Resonance And Fluorescence Enhancement Effects Of Ring-shaped And Rod-shaped Precious Metal Nanostructures

Under the excitation of the incident light,the free electrons in the metal will form a collective resonance with a positive charge as a background,which is called surface plasmon resonance.This resonance is usually confined to a very small area of the metal surface,and hence is called local surface plasmon resonance.For the isolated nanoparticles,the position of the resonance peak depends on the shape,size,symmetry of the nanoparticles,the direction of the excitation light,the direction of polarization and so on.When two nanoparticles are approached,the resonant modes of the two nanoparticles are mutually hybridized,and different hybridization modes appear under the influence of arrangement,spacing and other factors.The Fano resonance is the mutual interference generated by super-radiation mode and the sub-radiation mode.At the same time,the coupling of the surface plasmons of the two nanoparticles will produce a strong local field at the gap of the nanoparticles,and the excitation efficiency of the fluorescein will be greatly enhanced when the fluorescent species is near the region.This surface-enhanced fluorescence spectroscopy which based on surface plasmon resonance has been widely used in biological monitoring,imaging and other fields.Take the fact that the maturation of micro-nano-technology such as electron beam etching,it is possible to prepare complex and controlled metal nanostructured multimers.In our works,two kinds of metal nanostructures are designed,the coupling of plasmon resonance and the characteristics of the electromagnetic field enhancement are simulated by comsol software,this is help to experimental preparation and the later application.At the same time,taking into account the excellent fluorescence enhancement effect of metal nanostructure films and their application in sensing,we also prepared two kinds of gold nanorod films as the substrate,and using the nanorods on the substrate to produce enhanced local field realizes the fluorescence enhancement of the Rh6G probe molecule.The main work of this paper is as follows:1.The surface plasmon resonance properties of A novel multi-ring nanostructure are investigated.We designed a structure composed of three nanorings with different sizes,study the plasmon resonance characteristics of the structure by changing the size and position of two smaller nanorings,and analyzed the distribution of charge and electric field at the different resonances wavelengths.The result showed that ultrahigh order ring-ring surface plasmon resonances can be generated in the visible wavelength range,certain high order surface plasmon resonances can be either suppressed or enhanced when geometrical parameters of two inner rings are adjusted.It is reported that the suppression of the surface plasmon resonances can reduce mutual interference in spectroscopic measurement.By adjusting the position and size of one ring,some suppressed modes will reappear and the resonant modes of the same order appear in a variety of resonant ways.2.The resonant characteristics of asymmetry nanodisk-ring bilayer are investigated.The effect of rotating upper disk-ring on the surface plasmon resonance of the structure is studied.The result showed that the structure can produce adjustable Fano resonance,the dark dipole-dipole mode and dark quadrupole-quadrupole mode transferred to the long wavelength,widening the wavelength range of dark mode.At the same time,the structure also has a large refractive index sensitivity and the figure of merit,so this structure have potential applications in the sensor.3.The Au nanorod(Au NR)sols were prepared by seed growth method.The two-dimensional arrays of Au NR with different densities were assembled by an innovative self-assembly method.Surface-Enhanced fluorescence effect of Rh6G with Au NR substrate was observed.The results show that the larger the density is the best for the fluorescence enhancement of the molecule,and the local electromagnetic field enhanced around the Au NRs plays a crucial role in the fluorescence enhancement effect.4.The Au NR sols was prepared by the same method,and a two-dimensional array of periodic Au NRs was obtained by controlling the evaporation conditions.The dependence of the fluorescence enhancement effect of the Rh6G molecule on the polarization of the excitation light was investigated.The results show that the enhancement effect is strongly dependent on the polarization direction of the excitation light.Under 500 nm excitation light,the enhancement effect is the best when the excitation polarization agrees with the short axis of the Au NRs,and the enhancement effect weaker with the excitation polarization deviates from the short axis direction.The anisotropy of the Au NRs,the polarization direction of the excitation light,and the coupling effect between the Au NRs all play a crucial role.