SERS induced by two coupled monolayers of Au plasmonic nanoparticles

Highly efficient SERS substrates were prepared PLD and chemical methods by combining two quasi-homogeneous ∼1 cm² monolayers of 5-8 nm Au plasmonic coupled nanoparticles separated by chitosan based polymer film spacer thinner than 10 nm. Plasmonic modes of individual Au particles in each monolayer are coupled and form a 2D array of "hot-spots". Moreover, upon combining the monolayers in stack the plasmonic modes of neighbouring nanoparticles in different layers show also strong coupling. The variation of optical transmission of the nanosystem and its efficiency to enhance Raman spectra of Methylene Blue molecules are studied when polymer spacer thickness is altered. (paper)