Narrow Collective Plasmon Resonances in Nanostructure Arrays Observed at Normal Light Incidence for Simplified Sensing in Asymmetric Air and Water Environments

Abstract

We fabricate gold plasmonic nanoarrays on a glass substrate supporting narrow collective (diffraction coupled) resonances that can be excited with normal incident light in an asymmetric air or water environment. We measure quality factors of normal incidence resonances up to 19 in air, 45 in water, and 85 in glycerol and register a very high figure of merit for biosensing applications in water. The coupled dipole approximation is used to evaluate the optimum resonance conditions and qualitatively explain the properties of the resonances. Our results could help to develop simpler and cheaper surface plasmon resonance based approaches to gas and biodetection.