Biomedical Engineering Reference
In-Depth Information
demonstrated that Cu, Ag, and Au NPs are effective substrates for
SEF mainly because of their great resonance oscillation with light in
the UV-visible region.
7-16
The local electromagnetic (EM) environment of luorophores
on a metal surface is an important factor for controlling their
luorescence intensity. By taking advantage of the interaction of the
luorophore with its surroundings, dramatic improvements in its
luorescence can be achieved. The effect of the surrounding media
on the emission properties of luorophores was irst demonstrated
using free atoms in a high-Q cavity.
17
These improvements in
luorescence emission have been further realized in various systems
such as micropillars and microdiscs and more recently in photonic
crystal defect nanocavities.
18-22
A crucial challenge in SEF is the surface itself, which is designed
to control the luorophore emission and to induce the maximum
amount of luorescence in the direction of the detector. The surface
also modiies the excitation rate of a luorophore through altering
its local EM ield. Thus, a speciically designed surface together with
a precise excitation of optical geometry is another crucial aspect of
SEF. By altering the structure of a metal's surface, one can control the
properties of surface plasmons, in particular their interaction with
light. Surface plasmons are waves that propagate along the surface
of a conductor, usually a metal. When a conductor interacts with
light waves, its free electrons respond collectively by oscillating in
resonance with the light wave. The resonant interaction between the
surface charge oscillation and the EM ield of the light constitutes the
surface plasmon and gives rise to its unique properties. Due to their
high sensitivity to geometry and surroundings, surface plasmons
allow researchers to direct and focus light with subwavelength
optics.
23
Enhancements of the EM ields through surface plasmons
have been demonstrated in a variety of optical applications, including
non-linear optics.
24-26
In this chapter, we describe the impact of the interactions of
luorophores with metal NPs on their luorescence. The roles that
the nature of the metal surface and the distance of the luorophores
from it play in determining the luorescence are discussed from a
theoretical aspect. We also emphasize the detection of a number
of analytes, including DNA, proteins, and metal ions, using metal
NPs containing luorophores. The remarkable practical potential
of metal NPs-luorophore sensing systems is described. With their
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