Metal nanosphere at an interface: revival of degeneracy of a dipole plasmon

Metal nanoparticles supporting surface plasmon modes are used in many areas of science and technology. Often it is important to know the exact location of the metal nanoparticle relative to a larger dielectric object. In this paper, we demonstrate that this goal may be achieved by monitoring the localized surface plasma resonance splitting in the course of the nanoparticle movement. In particular, we simulate splitting of the plasma resonance localized in a metal nanosphere while it approaches and penetrates the interface of two dielectric media. Numerical simulations show that splitting goes through two maxima at the beginning and at the end of the penetration process while the plasmon modes become exactly degenerate at some distance near the midpoint of the nanosphere trajectory. These results may be used to real time monitoring of the exact position of the nanoparticles while they approach and penetrate different targets. Applications in the drug delivery, photodynamic therapy and other biomedicine branches are envisioned.