The Study Of Surface Plasmon Resonance And Surface Enhanced Raman Spectroscopy Under Evanescent Field Excitation

Surface plasmon is the collective oscillation of free electrons on metal surface,which is the result of the interaction of oscillation charge on metal surface and thefield of incident light. Surface plasmon has unique optical properties and has attractedgreat interests from people. With the increasing maturity of nanotechnology, surfaceplasmon has become the research hotspot. Its mechanism and application areintensively studied by researchers. Now surface plasmon has been widely applied inbiochemical sensing and surface enhanced Raman spectroscopy, in which thedetection sensitivity is the key issue. In this paper, in order to improve the sensing andRaman detection sensitivity, we design and prepare the surface plasmon substrate withnanostructures. The main contents include the following three aspects:1. The sensitivity of the surface plasmon resonance (SPR) sensor is the mostimportant parameter in evaluating its performance. In order to improve the sensitivityof SPR sensor, we introduce nanostructures on the prism surface. We prepare a silvernano-bowl array by using the template lithography and electrochemical depositiontechnique. The sensitivity of SPR sensor is improved by increasing the intensity ofsurface electromagnetic field.2. Surface enhanced Raman scattering (SERS) is a non-destructive spectrumdetection method, which can provide detailed information about molecular structures.The enhancing capacity of SERS substrate is the key issue in its high sensitivedetection. Here we design a surface plasmon nano-antenna, which is composed of aprism/silver nanowell array configuration. Through the Kretschmann prism, thecollection efficiency of the incident light is close to100%. The use of nanowell array can concentrate the collected light into nearfield, and produce a300timesenhancement in electric field intensity. In addition, through the nanowell array, we canalso control the SERS signal directional coupled emission for easy collection. In thedesign of this SERS substrate, the key issue lies in the improvement the collection andemission efficiency based on the antenna theory.3. For SERS enhancement contribution, hotspot, the regions on the substratewhich have intensive electromagnetic field plays a dominate role. Generally peoplecan often get hotspots in the following locations: positions between two nanoparticlesin close proximity, or sharp prominent surface. Here, different from the traditionalgap-or tip-type hotspot configuration, we propose a method combining opticalwaveguide and metal nanoparticles to enhance the local field intensity for SERSdetection. This SERS substrate has two enhancement contributions, one is from thewaveguide resonance, and the other is from the localized surface plasmon resonance.Under their combination effect, the local field around an isolated Ag nanoparticle canbe enhanced for about103times. Compared with general hotspots, in thisconfiguration the strongest electric field is located at the both sides of Agnanoparticles, which will have good performance in the detection of macromolecules.