Figure 35.

(a) Schematic depicting evanescent SPP waves and their excitation with a prism in a total internal reflection setup. The decay length l of the SPP determines its sensitivity to a film of different thicknesses. When the film thickness d is small compared to l, the SPP will probe the refractive indices of both the film and the bulk solution above the film. (b) Simulated SPR excitation. At the correct angle, SPPs are excited at 850 nm illumination for a 50 nm thick Au film. The inset shows a 1° shift in the SPP resonance dip when the bulk refractive index above the Au film changes from 1.32 to 1.33. This sensitivity of 100 deg/RIU (Refractive Index Unit) is typical for prism-based SPR instruments (Pang et al.).