Biomedical Engineering Reference
In-Depth Information
oleylamine ratio. The particles exhibited surface plasmon absorption characteristic
of Au and magnetic properties characteristic of Fe
3
O
4
, which are affected by inter-
actions between Au and Fe
3
O
4
. The dumbbell shape was formed through the
epitaxial growth of iron oxide on the Au seeds. The polarity of the solvent affected
this growth; for example, the use of diphenyl ether resulted in fl ower - like
Au- Fe
3
O
4
nanoparticles [26] .
Cho
et al.
[27] reported another method for directly attaching Au shells into the
iron oxide cores. In their study, Fe-core, Au-shell nanoparticles, of approximately
20 nm diameter, were synthesized using the reverse micelle method. Cho
et al.
[27] proposed that the Au shell appeared to grow by nucleating at selected sites on
the Fe core before coalescing. An examination of the nanoparticles, using trans-
mission electron microscopy (TEM), revealed rough shell surfaces that resulted
from the gold's less-than-ideal oxidation resistance. However, electrical transport
measurements in its pressed pellet form revealed the particles to be fairly stable,
as the resistance of the pellet did not change appreciably over time [27].
Caruntu
et al.
[28] successfully coated
10 nm Fe
3
O
4
nanocrystals with 2 - 3 nm
gold particles by using a chemically controlled, two-step procedure The fi rst step
in the process involved the formation of a stable methanolic solution of Fe
3
O
4
nanospheres coated with an amino-terminated silane, and peptized to induce posi-
tive charges on the particles' surfaces. The second step involved treating the par-
ticles with a colloidal solution of negatively charged Au nanoparticles to enable
the attachment of Au nanograins on the surface of the Fe
3
O
4
nanocrystals (Figure
7.2). These novel nanostructures opened up new opportunities for the use of
magnetite nanoparticles for
in vivo
biomedical applications through the chemical
bonding of bioactive molecules to the attached Au nanoparticles [28].
Lyon
et al.
[29] synthesized water-soluble, Au-coated magnetic Fe oxide nanopar-
ticles with diameters
∼
∼
60 nm. This was achieved by the reduction of Au
3+
onto the
surfaces of
- Fe
2
O
3
or partially oxi-
dized Fe
3
O
4
via iterative hydroxylamine seeding. The morphology and optical
properties of the core/shell particles were seen to depend on the quantity of depos-
ited Au, while the magnetic properties remained largely independent of the Au
addition. The Au-coated particles exhibited a surface plasmon resonance (SPR)
∼
9 nm - diameter particles consisting of either
γ
O
O
O
O
O
O
O
O
O
APTES
Au/THPC
O
O
O
O
O
O
O
O
O
-NH
2
Fe
2
O
3
@Au
Fe
2
O
3
nanoparticles
Figure 7.2
The formation of nanograin Fe
2
O
3
@Au
nanoparticles [28] . APTES, 3 - aminopropyltriethoxysilane;
THPC, tetrakis(hydroxymethyl) phosphonium chloride.
