Biomedical Engineering Reference
In-Depth Information
a microwave beam goes through the dielectric coating of the material,
radiation energy transforms into thermal energy and the material's
temperature increases [41].
Here, silver colloid was prepared by using chemical reduction method
[42, 43]. All solutions of reacting materials were prepared in Milli Q water.
In typical experiment 50 mL of 2 mM AgNO
3
was heated to boiling. To
this solution 50 mL of 2
◊
10
-4
trisodium citrate was added drop by drop.
h e solution was rel uxed at 80
C for 30 min. At er 15 min, clear solution
will change to pale yellow. h en it was removed from the heating element
and cooled to room temperature. Tri-sodium citrate being a weak reducing
agent cannot perform reduction at room temperature and merely serves as
a capping agent. Silver nanoparticles were isolated from the colloidal solu-
tion by centrifugation at 5000 rpm for 20 min and then washed 3-4 times
with water.
h ese nanoparticles were used as shell in preparation of core-shell
nanocomposites.
°
4.8 Gold Nanoparticles
Gold nanoparticles (GNPs) have attracted a wide range of interest because
of increasing applications in sensors, biosensors and many emerging areas
of nanotechnology. SPR bands of gold nanoparticles originate because of
the coherent excitation of free conduction electrons on nanoparticle sur-
faces as electromagnetic waves interact with nanoparticle surfaces and
the wavelengths of these bands depend on size, shape, and interparticle
dipole interactions [44]. For example, the study of the optical properties
of Au nanoparticles prepared by reverse micelles showed a red shit with
the particle size, which is expected from Mie theory. h e nanoparticles
are either inside the reverse micelles (for the smaller particles) or capped
with a monolayer of surfactants. h e comparison of the optical proper-
ties of nanoparticles with the predictions from Mie theory showed that the
resonance band of gold nanoshells on polystyrene cores could be tuned
across the visible and near-infrared range of the electromagnetic spectrum
by varying the amount of gold in the shells [45]. Au NPs have been studied
for their tunable optical properties in a wide spectral range as shown in
Figure 4.11. h e particle shows SPR band in the visible range of electro-
magnetic spectrum, position of which is dependent on various factors such
as size, shape and dielectric constant of the medium in which they are dis-
persed [44]. Previous studies suggest that SPR band of metal nanoparticles
could only be slightly varied by changing their sizes i.e in the range of 1 to
