(A) A prism-coupler setup (also known as Kretschmann setup) for the excitation of SPR in thin metallic films. (B) Coupling to surface plasmons is detected by a sharp reduction in reflectance at a certain excitation angle. Shown here is the simulated reflection of a 50 nm-thick gold film on a glass substrate as a function of incident angle for 850 nm illumination. By changing the refractive index of the solution by ∆n=0.01, the resonance (dip) shifts by 1° in this example, corresponding to the sensitivity of 100°/(refractive index unit). From Lindquist et al. .