Biomedical Engineering Reference
In-Depth Information
Synthesis of NMs is yet to be standardized and controlled to yield reproducible
results. There are a few guiding parameters that can be used to control the
size and the shape, which will be shown in some of the synthesis routes that
are featured in this chapter. These include the crystalline phase of nucleation
seeds, surface energy, and the choice of crystal growth regimes. The readers
are encouraged to try some of the routes presented and make changes to the
proposed methods to achieve different sizes and shapes of NMS.
2.1 INORGANIC NM
s
The inorganic NMs consist of elements that belong to the inorganic groups.
These can be semiconductors, conductors, single element or multielement in
composition. Among the semiconductors, QDs, gold and silver, metal oxides,
iron oxide magnetic NPs, and carbon nanotubes (CNTs) are the most popular.
QDs are semiconductor nanocrystals having diameters ranging between 2
and 8 nm,
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which are characterized by broadband excitation wavelength, nar-
row emission wavelength, very bright fluorescence even when lighted only with
a light emitting diode flashlight (
Figure 2.1
), and resistance to photobleaching;
they have emerged as a new class of fluorescent labels with better brightness,
resistance against photobleaching, and multicolor fluorescence emission.
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These may be synthesized from atoms belonging to elements in groups II and VI
(e.g., CdSe and CdTe) or groups III and V elements [e.g., indium phosphide
(InP) and indium arsenide (InAs)].
21-25
QDs can be made of a semiconductor
core (i.e., CdSe core) or coated with a shell (i.e., CdSe/ZnS core/shell) that
improves the optical properties. To make them soluble in water, they are capped
with a polymer or other materials that bring hydrophilicity to the NMs.
Among the range of available QDs, the ones composed of CdSe cores
over coated with a layer of zinc sulfide (ZnS) are produced by a range of
well-developed synthetic routes.
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These QDs become highly fluorescent and
exhibit attractive optical properties such as high quantum yield, large absorption
FIGURE 2.1
Digital photograph of water soluble QDs in vials under a 364-nm UV light.
By Z.P.
Aguilar
.
(For color version of this figure, the reader is referred to the online version of this topic)
