Surface plasmon resonance microscopy
Surface plasmon resonance microscopy (SPRM), also called surface plasmon resonance imaging (SPRI), is a label free analytical tool that combines the surface plasmon resonance of metallic surfaces with imaging of the metallic surface. The heterogeneity of the refractive index of the metallic surface imparts high contrast images, caused by the shift in the resonance angle.
Source: Wikipedia — Surface plasmon resonance microscopy (CC BY-SA 4.0)