Plasmonics and ultrasensitive detection

Abstract

An approach for experimental design in plasmon-enhanced spectroscopy is discussed based on its basic elements: electromagnetic radiation, adsorbed molecule and the metal nanostructure. Optimization of the plasmon enhancement may be achieved by tuning the electromagnetic radiation to take advantage of resonances with molecules and nanostructures. For instance, when the excitation is in resonance with a molecular electronic transition, resonance Raman scattering is observed providing a very efficient scattering with cross section for vibrational transitions several orders of magnitude higher than normal Raman. Tuning the excitation of the nanostructure might depend on the degree of aggregation, or the properties of two and three dimensional array of fabricated nanostructures. Several examples of surface enhanced Raman scattering (SERS), SERS and surface enhanced fluorescence using shell isolated nanoparticles are presented. The experimental results illustrate the remarkable optical properties of metal nanoparticles which are governed by the excitation of localized surface plasmon resonances producing local enhancement of the electromagnetic field. However, each experiment is unique and requires a selection of the setting for each one of the three elements that would lead to the most efficient plasmon enhancement.