Surface plasmons have been used to detect single molecular layers for many years. The most common examples are biosensor systems and the detection of self-assembled monlayers (SAMs). A surface plasmon is a two-dimensional electromagnetic wave that travels on the surface of a noble metal, most commonly gold or silver. This electromagnetic wave is extremely sensitive to changes in the dielectric constant 100 nm above the metal surface. When the dielectric constant above the metal changes due to the addition of a molecular layer, the intensity of the surface plasmon will decrease. In this way monlayers may be indirectly imaged on a a surface by mapping the surface plasmon intensity.