Biomedical Engineering Reference
In-Depth Information
Figure 10.6
Photograph showing the pale-yellow color solution of Ag NPs.
[46-50], dielectric-semiconductor [51, 52], dielectric-dielectric [53, 54],
semiconductor-metal [55], metal-metal [56], semiconductor-semicon-
ductor [57, 58], semiconductor-dielectric [59], metal-dielectric [60], dye-
dielectric [61], etc. Multishell particles can be visualized as core particles
having a number of shells around them. Core particles can be coated with
a shell to obtain a single nanoshell. Furthermore, this combination of core
and shell can be repeated again to get multishells.
h e plasmon resonance frequency can be systematically tuned by modi-
fying the radius r1 of the dielectric core and the total particle radius r2
[62]. Relative to the plasmon resonance of a solid spherical nanoparticle of
the same metal, the core-shell geometry allows the plasmon resonances to
be shit ed to lower energies. h e controlled synthesis of novel, uniformly
coated stable nanoparticles has for many years remained a technical chal-
lenge. Core-shell nanomaterials ranging from a few nanometers to a few
micrometers in size have been synthesized for a variety of purposes such
as novel catalysts [63], l uorescent diagnostic labels [64], avoiding photo
degradation [65], enhancing photoluminescence [66], creating photonic
crystals [67] and obtaining novel optical ef ects [68]. For metal nanoparti-
cles and nanoshells no band gap exists and the Fermi level lies in the center
of the band. h e relevant energy level spacing is very small and properties
resemble the continuum even in relatively small sizes (tens or hundreds of
atoms).
Some of the particles are SiO2/PAPBA Poly(3-aminophenylboronic
acid), Ag2S/ PVA (Polyvinyl alcohol), CuS/PVA, Ag2S/PANI (Polyaniline)
and TiO2/cellulose. Another type of core shell nanocomposite is one in
which the core of particles consists of organic compounds and can be
polymers of organic compounds. h e shell is inorganic and is a metal or
silica or silicone. Structures that fall under the category of polymer/metal
are polyethylene/silver and polylactide/gold. Some particles have a poly-
meric core and a polymeric shell and are dispersed in a matrix, which can
be any material whose property is to be modii ed. One of the materials
