Biodetection Based on Fluorescence Quenching and Surface-Enhanced Fluorescence Using Noble Metal Nanoparticles - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 222

by the rear side. The Kretschmann coniguration indicates that the
index of refraction of the material on the rear side is higher than the
one on the front side as shown in Fig. 10.5(A).

(B)

(A)

Figure 10.5 (A) A schematic representation of the Kretschmann optical
coniguration for the three layer stacking glass/metal/
dielectric. The index of refraction of the glass prism n g is
higher than the one of the dielectric n d . (B) Dispersion
curves for the Kretschmann coniguration showing that the
resonant coupling between light and SPP is possible when
the light cone crosses the SPP dispersion curve. The in-plane
momentum for a given incident angle θ is increased by Δ k , in
which Δ k = ω ( n g - n d )/ c , ω is the angular frequency and c is
the speed of light. Reprinted with permission from Ref. 13.

When illuminating the metallic thin ilm at an angle θ 0 , the light
in-plane wave vector is k || = n g k 0 sin θ 0 , in which n g and k 0 are the
index of refraction of the glass prism and the momentum in free
space, respectively. The dispersion relation for the SPPs propagating
on the opposite side of the metallic thin ilm can thus be satisied for
a given incident angle θ SP as shown in Fig. 10.5(B). The excitation
of the SPP occurs at the minimum of the relected intensity. At the
resonant angle for SPP excitation, the relected intensity equals zero
for a speciic thickness d c of the metallic thin ilm. 38 At the same
time, the EM ield reaches its maximum at the metallic surface on
the opposite side. The ield can be signiicantly enhanced when
compared to that with a similar coniguration without the metal. 39
In order to represent the enhanced factor of the EM ield both
with and without using a metal, enhancement ( G ) is used. G is deined