Biomedical Engineering Reference
In-Depth Information
A seed-mediated growth method was later developed for several
types of gold nanostructures, such as nanorods
23,25
and nanoshells.
Gold nanoshells, consisting of a dielectric core with a gold shell
of nanometer thickness, were reported by a preparation scheme
applying the similar seed-mediated growth method to the coating
on a relatively large silica particle.
29
Later, the preparation of hollow
gold nanoshells was demonstrated to be achieved through reacting
aqueous HAuCl
4
solutions with solid templates such as silver
nanoparticles.
30
More recently, gold nanocages were irst synthesized by the use
of a polymer-assisted followed by a galvanic replacement reaction
between solutions containing gold precursor salts and silver
nanostructures prepared through polyol reduction.
31
1
.
3
Optical Properties of Noble
Metal Nanoparticles
The interaction of light with small metal nanoparticles has been of
great interest for many years. The visible colors of a few kinds of noble
metal nanoparticles are due to the resonant excitation of a collective
oscillation of the conduction electrons in the particles termed
surface plasmons. The plasmon-related optical properties of metal
nanoparticles strongly depend on the size,
32
shape,
33
composition,
and surrounding medium of nanoparticles.
34
In this section,
typical optical characteristics of noble metal nanoparticles, such as
luorescing, absorption, and scattering are summarized, respectively.
The main focus is to present the absorption and scattering spectra for
rod-like metal nanoparticles dispersed in water. To further illustrate
the transverse and longitudinal components in the associated
spectra, the overall absorption spectra were deconvoluted to further
relect the material-dependent trend.
1
.
3
.
1
Fluorescing Noble Metal Clusters
The luorescence of metal clusters and thin ilms is well established
based on the observation of photoluminescence from bulk copper and
gold,
35
and on the photoinduced luminescence from noble metals.
36
For example, the photoinduced luorescence from Ag
3
clusters was
observed to center around 500 nm.
37
Silver nanoparticles in water
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