Biomedical Engineering Reference
In-Depth Information
Figure 4.11
TEM image of prepared SiO
2
@Ag nanocomposites.
(0.05 gm dispersed in 10 mL of water) using trisodium citrate (50 mL,
2
◊
10
-2
M). h ese particles were centrifuged and washed with water. Yellow
colour precipitate was again redispersed in water. To enhance the thick-
ness of coating the second step was repeated again till the desired thick-
ness was obtained. Coating thickness can also be controlled by modifying
the reaction conditions such as amount of silica particles added. SiO
2
@Ag
coreshell particles were isolated from the colloidal solution by centrifuga-
tion at 4000 rpm for 20 min and then washed 3-4 times with water. h e
prepared nanocomposites were observed using TEM as is clearly shown in
Figure 4.11.
In order to prepare SiO
2
@Au particles i rst the silica particles was func-
tionalized using 3-Aminopropyltriethoxysilane (APTES). APTES mol-
ecules have one
−
OH end and the other end has
−
NH
4.
So it was bonded
to silica through oxygen and gold via nitrogen atom. Functionalization of
silica particles was performed by using 12 mM APTES in C
2
H
5
OH:H
2
O
(3:1volume ratio) and adding silica particles to it with APTES: silica ratio
as 4.3:1 by weight. h e resulting solution was vigorously stirred at 75
C for
4 h. h e solution was centrifuged and washed with water. Functionalized
particles were then re-dispersed in water.
Speckled SiO
2
@Au core shell particles were synthesized in a three step
procedure [57-58] as follows 1) 20 mL (6.25 mM) of gold solution, 4.5
mL (0.1 M) of NaOH solution (pH = 7.0) and 1 mL functionalized silica
particles in water were stirred at 75
°
C for 10 min. h ese form the gold
seeds with silica particles. Above solution was centrifuged, washed with
water and re-dispersed in 40 mL water. (2) 28 mg K
2
CO
3
, 100 mL Milli-Q
water and 1.5 mL of 25 mM gold sol solution were poured in 250 mL round
°
