Plasmonic Materials and Nanospectroscopy

Santiago Sanchez-Cortes

Institute of Structure of the Matter, Spanish National Research Center, Spain

Abstract
Plasmonics is based on the interaction of light with materials in the nanoscale. The large local enhancements of the incident electromagnetic (EM) field in the proximity of nanostructured metals, as a consequence of the localized surface plasmon resonance (LSPR) have advanced applications in photonics, electronics and optical spectroscopy. Plasmonic-enhanced phenomena gives rise to large enhancements of the cross section of Raman and fluorescence emissions and the IR absorption leading to the so-call Surface-Enhanced Raman scattering (SERS), Surface-Enhanced Fluorescence (SEF) and Surface-Enhanced IR Absorption (SEIRA) techniques. In this work we report the fabrication of plasmonic nanoparticles with a high performance in Surface-enhanced spectroscopy or what it is now called Nanospectroscopy. In the last times we have devoted much attention to the fabrication of silver triangular nanoprisms and nanostars with a high SERS effectiveness. These NPs were applied in the detection of sport doping drugs detection. The formation of size-controlled nanogaps between NPs or in NP/films is another system where LSPR is possible. The interest of these gaps resides in the huge enhancement of the optical response of substances situated in these points, which is indeed highly valuable for the design of sensitive systems with advanced applications in molecular detection. An ideal situation for building nanogaps is the use of bifunctional molecules which act as NPs linkers. In this work I show that nanogaps can be formed by linking NPs by means of aromatic and aliphatic molecules. The interest in the effect of bifunctional molecules on NPs resides on the creation of HSs and the chemical modification on the surface localized in this highly important points. The functionalization of metal NPs leads to the modification of the chemical properties of the surface that further potentiate the performance of plasmonic devices. This method is an important process in the analytical applications of SERS and SEF due to the fact that the affinity of adsorbates toward the metal surface is highly affected by the nature of the metal interface. In this work I report the functionalization with several cavitands: calixarenes and cyclodextrines, and the bifunctional viologens in the detection of pollutants. A study of the adsorption of these molecules on the surface was previously performed in order to optimize the functionalization process in terms of surface coverage and structure of the selected molecular links. Finally, we also report the application of some of the SERS platforms fabricated in our laboratory in the frame of the Cultural Heritage. The application in this case was performed with the goal of obtaining information about the organic compounds employed in artworks, since these molecules are difficult molecules to be studied due to their high fluorescent emission. To accomplish this SERS study plasmonic NPs were fabricated in-situ by laser photoreduction, what have permitted the study of very small amounts of materials and the analysis of minute amounts of the organic pigments and dyes.