Preparation And Design Of Silver Nanowires And Its SERS Studies

Surface-enhanced Raman spectroscopy (SERS) has attracted ever increasing attention due to its high sensitivity, specificity, and fingerprint effect in the detection of a variety of molecules. In general, two important challenges should be taken into consideration for SERS for ultrasensitive detection of molecules and biomolecules: how to create a SERS-active substrate with both good reproducibility and high sensitivity. silver nanocrystals with well-defined and controllable shapes areemployed as SERS-active substrates because of their remarkable plasmonic properties and resulting unique SERS performances. In addition, high-aspect ratio silver (Ag) nanowires have large surface areas and high crystallinity, which make them an ideal SERS candidate. However, due to the momentum mismatch between the photon and the propagating plasmons on the nanowire, the coupling of light into the plasmon modes are weak and SERS"hot spots"are limited to the ends of the nanowire Many studies have been focused on addressing these challenges. In this thesis, three parts of works have been investigated about silver nanowires and its SERS substrates were designed:(1) In this work, high-aspect ratio silver nanowires have been synthesized by a polyol process. A detailed parametric study determining the relationship between final morphology of the products and temperature, molar ratio of poly(vinylpyrrolidone) to silver nitrate, sodium chloride amount, and different kinds of polyols is presented. The as-synthesized silver nanowires are analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction(XRD) and Ultraviolet-visible spectrometer(UV-vis). The dependency of nanowire morphology and aspect ratio on synthesis parameters is shownvia SEM images.(2) In order to create the effective number of surface-enhanced Raman scattering (SERS) active "hot spots" on the one-dimensional nanostructure surfaces for ensuring the maximum enhancement of SERS signal, smooth silver nanowires (Ag NWs) were firstly synthesized by the conventional polyol method, and then the smooth silver nanowires were subjected to chemical etching by the Fe(NO3)3aqueous solution at room temperature to obtain corrugated silver nanowires. The SEM images showed that the surface roughness of silver nanowires was dependent on the amount of Fe(NO3)3, by increasing the amount of Fe(NO3)3added into the silver nanowires solution, the surface of silver nanowires become more and more rough. However, as the excess amount of etchant added, most silver nanowires would broke off into shorter rods, and even spherical particles. Raman analyses of CV indicated that the SERS intensity changes depending on the surface roughness of etched silver nanowires, and the silver nanowires with corrugated surfaces exhibited higher enhancement of SERS signal than the smooth silver nanowires. In addition, the SERS detection of CV and4-Mpy molecules exhibited high detection sensitivity and the detection concentration were as low as10-10M and10-9M, respectively, which means that the corrugated silver naowires could be an efficient SERS active substrate.(3) The homogeneous surface-enhanced Raman scattering (SERS) active hot spots on a SERS substrate is the most crucial factor in ensuring their application a reproducible and ultrasensitive sensing platforms. In this paper, we report on a simply shaking-assisted liquid-liquid (water-chloroform) interfacial assembly process for fabricating aligned Ag nanowire (AgNW) two-layer films on solid substrates. A scalable fabrication process can be easily realized by using a large size of container. These AgNW two-layer films can be used as ideal SERS active substrates for chemical and biomolecular detection with highly sensitivity and excellent reproducibility. Significantly, sensitive and quantitative detection of carbaryl with a detection limit of10-7M (0.1ppm) using these SERS substrates to demonstrate potential applications for environmental pollutant analysis...