Biomedical Engineering Reference
In-Depth Information
display enhanced luminescence from luorescein, DNA can be
detected.
All presently used DNA assays rely on extrinsic probes (labeling)
that are used to impart strong luorescence to intrinsically
nonluorescent DNA. Because this labeling usually requires time
consuming processes and produces undesirable byproducts,
techniques that allow for the detection of DNA though its intrinsic
luorescence are desired. When DNA is adjacent to a metal surface, its
radiative decay rate increases after being excited by UV light, leading
to the enhanced intrinsic emissions of DNA.
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There are several
commercial UV lasers for this purpose, including Ar ion lasers, ArF
excimer lasers, Nd:YAG lasers, and several others. One problem with
using UV lasers for excitation is the luorescence interference from
sample matrixes such as proteins. In addition, UV lasers are usually
more expensive, and their maintenance is usually more necessary
and costly. These problems can be overcome by using visible or NIR
lasers when applying two-photon or multiphoton excitation. Metal
NPs can accelerate two-photon or multiphoton excitation due to
enhanced local EM ields.
10.3.3 OtherApplications
Fluorescence microscopy is a prevalent technique for cell imaging.
Although systems for obtaining high resolution cell images are
available, systems that allow for the simultaneous monitoring of a
number of cells are still necessary when statistical investigations
are conducted. Such systems require both low magniication to
obtain a reliable statistical population and high contrast to obtain an
accurate diagnosis of the nature of the cells' perturbation. Because
microscopic objectives with low magniication generally yield low
collection eficiency, such studies are limited by the luorescence
signal weakness. To overcome this technological bottleneck, metal-
coated substrates that enhance the luorescence process and
improve collection eficiency in epiluorescence observations are
used in commercial microscopes.
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The presence of a relective
surface modiies both the excitation and emission processes and
additionally reshapes the luorescence emission images. This system
produces increased luorescence signal from a layer of Cy3 dye on
a substrate by a factor ~30. Metal plasmon-coupled probes have
been demonstrated for the luorescence imaging of HEK 293 A and
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