Distinct plasmonic manifestation on gold nanorods induced by the spatial perturbation of small gold nanospheres.

The plasmon coupling between a Au nanorod and a small Au nanosphere has been studied with scattering measurements, electrodynamic simulations, and model analysis. The spatial perturbation of the nanosphere leads to distinct spectral changes of the heterodimer. The plasmonic responses, including Fano resonance, are remarkably sensitive to the nanosphere position on the nanorod, the gap distance, and the nanocrystal dimensions. The nanosphere dipole is intriguingly found to rotate around the nanorod dipole to achieve favorable attractive interaction for the bonding dipole-dipole mode. The sensitive spectral response of the heterodimer to the spatial perturbation of the nanosphere offers an approach to designing plasmon rulers of two spatial coordinates for sensing and high-resolution measurements of distance changes.