surface plasmon resonance

Surface plasmon resonance is a measurement method that shines light on the surface of an extremely thin metal film to read, in real time, molecules attaching to and detaching from that surface. Think of it like a scale needle shifting when you place something on it versus nothing at all: even a single molecule sticking to the metal surface slightly changes the angle or intensity of the light reflected from that surface. By precisely reading this change, you can extract numbers for how strongly two molecules grip each other, how long it takes them to bind, and how long it takes them to separate.

When designing new drugs or new proteins, this technique is one of the standard methods for measuring binding strength (expressed as a KD value). No matter how sophisticated a computer's binding predictions are, an actual lab step is still needed to bring the two molecules together and measure their strength directly — and this is a commonly used tool for that verification step.