Surface plasmon resonance - Wikipedia
https://en.wikipedia.org/wiki/Surface_plasmon_resonanceThe surface plasmon polariton is a non-radiative electromagnetic surface wave that propagates in a direction parallel to the negative permittivity/dielectric material interface. Since the wave is on the boundary of the conductor and the external medium (air, water or vacuum for example), these oscillations are very sensitive to any change of this boundary, such as the adsorption of molecules to the conducting surface.
Localized surface plasmon - Wikipedia
https://en.wikipedia.org/wiki/Localized_surface_plasmonThe plasmon resonant frequency is highly sensitive to the refractive index of the environment; a change in refractive index results in a shift in the resonant frequency. As the resonant frequency is easy to measure, this allows LSP nanoparticles to be used for nanoscale sensing applications. Also, nanoparticles exhibiting strong LSP properties, such as gold nanorods, could enhance the signal in surface plasmon resonance sensing. Nanostructures exhibiting LSP resonances are us…