Biomedical Engineering Reference
In-Depth Information
(g)
(a)
(c)
(e)
(b)
(d)
(f)
500 nm
(h)
(i)
50 nm
Figure 9.3
Magnetic/luminescent nanoparticles in white light
(a,c,e) and ultraviolet (b,d,f) illumination, either dispersed
(a,b) or close to a magnetic fi eld (c,e,d,f). Scanning electron
microscopy (g) and TEM (h,i) of the Fe
3
O
4
@SiO
2
core - shell
materials with the visible luminescent band in (i).
Reprinted with permission from Ref. [78];
© The American Chemical Society.
50 nm
the magnetic material a greater stability in harsh chemical and physical environ-
ments (e.g., low- or high-pH waste streams). Although, until recently, the synthesis
of these materials has been expensive and required specialized equipment, more
recent reports have described the development of synthetic techniques to produce
core-shell material, using much less specialized equipment [62, 83]. As an
example, Wang
et al.
[63] described a solution-based method that involved the
preparation of oleic acid-stabilized iron oxide nanoparticles for incorporation into
carbon spheres; this method employed hydrothermal techniques with a carbon
source derived from glucose. By carefully controlling the ratio of nanoparticles to
glucose, it was possible to create carbon spheres of approximately 100- 200 nm
diameter, into which iron nanoparticles were embedded. Likewise, Xuan
et al.
[64]
described a one-step method using an iron salt, urea, and glucose in an autoclave
to generate a 100 nm ferromagnetic magnetite core with a
30 nm carbon shell,
as shown in Figure 9.4. Although the particles exhibited a ferromagnetic behavior,
with a saturation magnetization value of
∼
42 emu g
− 1
(this was less than the bulk
material, but a less dramatic loss than seen with silica encasement), their increased
stability and ease of functionalization compared to the non- core - shell materials
suggested that they might be potentially useful materials for environmental
sensing applications.
∼
9.2.2.3.1
Precious Metal Encapsulation
Encapsulation of the magnetic nanopar-
ticle core with a metal coating can have a variety of benefi ts, as the loss of magnetic
behavior seen with silica coating (and, to a lesser extent, with carbon coating) does
