observance that, although numerous commercial SPR systems are available, their
designs are very similar to that which was originally presented by Liedberg etal.
(1983). Figure 8.2 depicts a typical Kretschmann SPR sensor conguration with
angular modulation. In this setup, using a prism as an optical coupler, a focused
monochromatic incident light beam is totally reected at the metal–dielectric inter-
face. An electromagnetic eld component, commonly termed an “evanescent wave,”
excites surface plasmons within the metal layer. The strength of coupling between the
incident wave (K
) and the resulting surface plasmon wave (SPW or K
) is observed
at multiple angles of incidence of the incoming light wave. The angle of incidence
which yields the strongest coupling (i.e., maximum absorbance) can be identied by
monitoring the reected light using a simple light detector array which is used as the
sensor output. This output can then be calibrated to the corresponding RI value at
the sensor surface on the sample side. Figure 8.3 shows a typical angle-based SPR
Incident light (K
to be detected)
FIGURE 8.2 A typical Kretschmann SPR sensor setup.
Angle of incidence
FIGURE 8.3 A typical Kretschmann SPR response prole. A change in the sample RI causes
a corresponding shift in the SPR angle (i.e., the dip location of minimum reected intensity).