Plasmon ruler with gold nanorod dimers: utilizing the second-order resonance

The idea of utilizing the second-order plasmon resonance of the gold nanorod {\pi}-dimers for plasmon rulers is introduced. We report on a qualitatively different dependence of the plasmon resonance shift on the interparticle distance for the first- and second-order longitudinal modes, extending the working range of plasmon rulers up to the distance values of 400 nm.