Controlled Decoration Of Silver Nanocrystals On Nanofibers And Their Sere Performance

Surface-enhanced Raman scattering (SERS) can provide the ultrasensitive detection of various biological and chemical species down to trace level and has potential applications in various fields. It is well known that "hot spots" make a major contribution to SERS, and the Raman intensity will be amplified by 103-1011 times when the analyte molecules are adsorbed around the "hot spot which usually reside in the interstitial site consist of two or more coupled nanoparticles and metals with intersection, biofurcation and high radius of curvatures. Therefore, assembly nonspherical noble metal nanoparticles with high density on the surface of substrate will improve the SERS property greatly. As an SERS substrate, nanofiber possess the extremely large surface area to volume ratio which provides nanofibers with additional binding sites for absorbing analyte molecules, improving the sensitivity of the prepared substrate. Here, in this paper, the preparation, mechanism and SERS property of nonspherica silver nanocrystals-decorated nanofiber mats were carry out by the following parts.1. First, the PmPD/PAN shell/core nanofiber mat was prepared by simple chemical oxidation method. Then the silver nanocrystals (polyhedron and nanoplate)-decorated polyacrylonitrile (PAN) nanofiber mats were obtained by chemical deposition. The effect of the experimental parameters, such as temperature, concentration and pH of [Ag(NH3)2]OH aqueous solution, on the morphologies evolution and density of AgNCs are systematically investigated. The plate-like and polyhedral AgNCs-grafted PAN nanofiber mat provide not only abundant "hot spots" but also high surface area for absorbing plenty of analyte molecules, thus rendering the high SERS sensitivity. The results suggest that the optimized nanofiber mat exhibits significant SERS performance with superior stability and reproduction, and the SERS detection limit can reach 10-9 for 4-sulphur benzoic acid (4-MBA).2. This part report a facile method to synthesise flexible 3D surface-enhanced Raman scattering (SERS) substrates, using poly-m-phenylenediamine/polyacrylonitrile (PmPD/PAN) nanofiber mats as templates to self-assemble citrated-stabilized Ag nanocrystals (AgNCs). The effect of the extinction wavelength as well as the density and morphology of the AgNCs on the SERS enhancement effect was explored. The results suggest that the 3D AgNTs@PmPD/PAN nanofiber mat exhibits the highest SERS sensitivity and the lowest RSD value. The detection limit of 4-MB A is as low as 10-8 M, making the nanofiber mat a promising candidate for the SERS detection of chemical molecules.3. This part report a new simple method to fabricate a high-active SERS substrate consisting of poly-m-phenylenediamine/Polyacrylonitrile (PmPD/PAN) decorated with Ag nanoplates. The formation mechanism and the phenomenon of Ag nanoparticles turn into Ag nanoplates during the self-assembly are systematically investigated. The synthetic process of Ag nanoplates-decorated PmPD/PAN (Ag nanoplates@PmPD/PAN) nanofiber mat consist of assembly of Ag nanoparticles on the surface of PmPD/PAN nanofiber as crystal nucleus and in situ growth of Ag nanoparticles into exclusively shaped as nanoplates. Both the aging time and the reducibility of polymer play important role on the formation of Ag nanoplates. The optimized Ag nanoplates@PmPD/PAN nanofiber mat exhibits excellent activity and reproducibility in SERS detection of 4-sulphur benzoic acid (4-MBA) with detection limit of up to 10-10 M, makes the Ag nanoplates@PmPD/PAN nanofiber mat a promising substrate for SERS detection of chemical molecules.