Surface Plasmon Resonance

The SPR technique is based on a complex optical phenomenon. When photon reaches the interface of two medium with different refractive indexes at a specific angle range, the resonant oscillation of surface plasmon generated by metal free electron can be induced. The resonance also requires that the frequency of incident photon matches the natural oscillating frequency of the surface plasmon. https://www.profacgen.com/surface-plasmon-resonance-spr-service.htm