SPR is an optical sensing technique to monitor biomolecular interactions in real time. It works by passing light through a prism, where it bounces off the back of a gold coated surface, and into a detector. At the specific resonance angle, the electrons in the metal film of the gold surface absorb the light, causing the electrons to resonate, called surface plasmons.

The absorption of light causes a dip in intensity of the reflected light at the resonance angle. The shape and location of this dip can be used to calculate information about the surface. When a molecular binding event takes place to change the molecular structure of the surface investigated, the angle of resonance changes. Heightened sensitivity, detection principle and sample fluidic design make SPR particularly well suited to quantify the affinity and rates of biomolecular interactions.