Biomedical Engineering Reference
In-Depth Information
(a)
(b)
15
10
5
0
0
100
Fe
3
O
4
Diameter (nm)
50
150 200
140 nm
110 nm
(c)
(d)
carbon
magnetite
Fe
3
O
4
111
carbon
0.48 nm
311
220
30 nm
4 nm
Figure 9.4
Transmission electron microscopy (TEM) images
of carbon - coated Fe
3
O
4
. (a,b) Low magnifi cation; (c) High
magnifi cation; (d) High-resolution TEM image of a typical
Fe
3
O
4
@C particle. Reprinted with permission from Ref. [64];
© IOP Publishing.
not always occur when select metals are used. Additionally, the metal itself can
aid in the sensing application. For example, when gold or silver is used to coat the
Fe
3
O
4
, small changes in the dielectric environment close to the particle surface
can result in wavelength shifts in the surface plasmon peaks, making such par-
ticles excellent sensing materials for biological applications.
The coating of iron oxide nanoparticles with gold has the advantage of an
increased choice of functional ligands by exploiting the strong gold- thiol interac-
tion, the plasmonic peak at 520 nm, and also the reduced drop in overall saturation
magnetization of the core-shell magnetic nanoparticles. Numerous methods have
been developed for the preparation of Fe
3
O
4
@Au core - shell materials using
microemulsion techniques [84, 85], citrate reduction [86, 87], the deposition of the
noble metal to the Fe
3
O
4
surface by heat and/or sonication [69], and the deposition
of Au nanoparticle seeds onto the iron oxide nanoparticle surface [65, 66]. Most
of these methods allow the gold shell thickness to be tuned simply by adjusting
