Study On Three-Dimensional Nanostructures’ Hotspot And Its Surface-Enhanced Raman Scattering

Surface Enhanced Raman scattering (SERS) is a widely-used technique in various fields because of its high sensitivity and abundant stuctural information. Generally,"Hotspots" in noble-metal nanostructures are considered as the major sources of Raman enhancement. The electromagnetic field strength will be greatly enhanced in such hotspots, so that the Raman enhancement factor can be increased by several orders of magnitude and even single-molecule detection is achieved. Preparation of SERS-active nanostructures with high density of hotspots is an important method to improve the sensitivity and repeatability of SERS detection. Great progress of SERS has been made since the continuous development of the technology for nanostructure preparation and assembly. Theoretical and experimental studies have shown that the hotspots located in compact and efficient three-dimensional (3D) plasmonic structures are of great significance for the detection of SERS.3D hotspots enable SERS to beame a fast, efficient technique of detection. Nowdays,3D plasmonic structures have attracted many reseach interests in both the plasmonics and SERS fields. Understanding and unravelling the distribution and enhancement mechanism of hotspots in3D nanostructures is the premise for high sensitivity and high reproducibility of SERS detection. All above issues constitute the main research contents in this thesis.Chapter1mainly introduces the SERS discovery, development, enhancement mechanism, hotspots, and different plasmonic structures including zero-dimensional point-like, one-dimensional linear, two-dimensional planar, and3D steric geometries.Chapter2studies the effect of surface/interface properties on3D hotspots. A droplet of the mixture of silver sol and SERS reporters is droped on the silicon for real-time measuring. In the evaporation process, the nanoparticle assembly can produce3D hotspot matrix on hydrophobic surface, and the Raman enhancement and reproducibility of SERS will be improved remarkably. This method can be used to achieve ultrasensitive detection of R6G, CV, PATP and other molecules. The capillary force-mediated assembly provides an effective way to build3D hot spot matrix.Chapter3studies a novel SERS detection in a hanging droplet of nanoparticle sols and its formation mechanism of3D hotspot matrix. The mixed colloidal suspension hanging on the bottom of quartz glass panel, the hanging droplets used as dynamic substrate for signal acquisition during evaporation process. The laser focuses on the center of the bottom and penetrating the quartz glass for successful SERS measurements. The hanging method can not only concentrate the nanoparticles and molecules, but also prevent the particles from attaching to the edge of the droplet, and3D SERS hotspot matrix can be constructed during the detection process.Chapter4and5reports the synthesis, SERS perfomance, hotspot distribution, and plasmonic photocatalysis of three anisotropic noble-metal micro-structures, inculding gold microtriangle (AuMT), gold microhexagonal (AuMH) and gold microcube (AuMC). Combined the theoretical FDTD simulation, the anisotropy distribution of electric field is graphically illustrated. A plasmonic photocatalytic reaction is studied on AuMT and AuMH, respectively, to exploring the concentration effect on the hotspot enhancement. For the first time, the relationship between plasmonic photocatalytic activity and SERS performance of the corners, edges and faces of each microplate is graphically illustrated.