Substrate-induced Fano resonances of a plasmonic nanocube: a route to increased-sensitivity localized surface plasmon resonance sensors revealed.

Symmetry-breaking introduced by an adjacent semi-infinite dielectric can introduce coupling and hybridization of the plasmon modes of a metallic nanostructure. This effect is particularly large for entities with a large contact area adjacent to the dielectric. For a nanocube, a nearby dielectric mediates an interaction between bright dipolar and dark quadrupolar modes, resulting in bonding and antibonding hybridized modes. The Fano resonance that dominates the scattering spectrum arises from the interference of these modes. This analysis provides a strategy for optimizing the sensitivity of nanostructures, whether chemically synthesized or grown by deposition methods, as high-performance localized surface plasmon resonance sensors.