Surface plasmon resonance
Surface plasmon resonance (SPR) on gold is one of the
most widely used methods for determining binding constants.
The method is based on the principal that the angle of
maximum extinction of the plasmon on gold is strongly
dependent on the index of refraction of the medium.
This technique is illustrated in the following. In the first
scheme a particle angle gives a minimum for a particular
sample cell. When a binding even takes place on the gold
surface, this results in a shift in the minimum angle. The
detection of this shift results in a determination of the
amount of binding. The concept is illustrated schematically