Biodetection Based on Fluorescence Quenching and Surface-Enhanced Fluorescence Using Noble Metal Nanoparticles - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 217

intensities. The second term Z ( ω em ) describes the partition of
energy into the radiative and nonradiative decay pathways near a
metal surface. The production and its effect on the decay rate of a
luorophore with enhanced local ields have been demonstrated in
the presence of ellipsoidal particles with a maximum enhancement
of the magnitude about 140. 29
Metallic spheroids affect the spectral properties of nearby
luorophores. 30-33 Figure 10.3 illustrates the changes in the radiative
rates for a luorophore at various distances from the surface of a Ag
particle and for different orientations of the luorophore transition
moment.
Figure 10.3 Effect of a metallic spheroid on the radiative decay rate of a
luorophore. The resonant frequency of the dye is assumed to
be 25,600 cm −1 , approximately equal to 391 nm. The volume
of the spheroids is equal to that of a sphere with a radius of
200 Å. Reprinted with permission from Ref. 28.
In this study, the Ag particle is an ellipsoid with an aspect ratio of
a / b , in which a and b are the long and short axes, respectively. The
luorophore is located outside the particle on the long axis at a
distance r from the center of the spheroid and a distance d from the
surface. The orientation of the luorophore can be parallel or