Biodetection Based on Fluorescence Quenching and Surface-Enhanced Fluorescence Using Noble Metal Nanoparticles - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 216

different from the effects of the collision quenching rate k q [ Q u ], in
which k q is the collision quenching constant and [ Q u ] is the quencher
concentration. In the case of collision quenching, both the lifetimes
and quantum yields decrease (see Fig. 10.2). On the other hand,
increases in Γ m in the presence of metallic colloids cause a decrease
in τ m but an increase in Q m .

Figure 10.2 Comparison of Stern-Volmer plots for collisional quenching
and colloids which enhance Γ m . Reprinted with permission
from Ref. 28.

In addition to quenching, an enhanced local ield and an
increase of the radiation decay rate of the luorophore affect the Q m
of a luorophore near a metal surface. When these two effects are
considered, we use the apparent quantum yield ( Y ) to substitute for
Q m .

2

YL =( ) ( )

ω

Z

ω

(10.5)

ex em

The irst term L ( ω ex ) describes the local intensity that is
proportional to the product of the quantum yield without a metal
present and the ampliication of the incident ield. Since the light
intensity is proportional to the square of the local electric ield, a
metal can induce a signiicant enhancement in the local excitation