Biomedical Engineering Reference
In-Depth Information
different size and shape to tune some specific property of interest. For example, some nanoparticles
can present different colors in function of their sizes because of the modification in the electronic
band gap of semiconductors (
Figure 9.1
) or in the surface plasmon band of metals (
Figure 9.2
).
Moreover, the shape and symmetry of a nanoparticle are as important as the size on the energetic
properties.
One fundamental aspect of all nanoparticles is the high surface area to volume ratio
[6]
. When
an atom is on the surface of a nanoparticle, its coordination number presents imperfections, which
causes a spontaneous contraction of the remaining bond. This bond contraction can be associated to
a potential energy depression that increases the interaction between electrons and the nucleus of
this atom, which enhance the local density of charge, modifying significantly the chemical proper-
ties of the surface. It means that the surface of a nanoparticle is much more reactive than any flat
surface of similar composition and any reaction that occurs on the surface of the nanoparticles will
be immediately accelerated.
It is not difficult to imagine the impact of the nanoscience in the field of human health, particu-
larly in dentistry with treatment opportunities that may include the formulation of functional denti-
frices, tooth repair, dentition renaturalization, drug delivery for local anesthesia, teeth prosthesis
with superior performance, antimicrobial action and oral cancer treatment and diagnostics. The
advent of the nanotechnology resulted in a new paradigm in several fields, and because of their
interdisciplinary character, the potential of nanodentistry to improve the welfare of our society will
be achieved only through an intensive and collaborative work of researchers and experts from
different fields.
Absorption/
emission
1.4
Relative narrow
emission
(30-35 nm FWHM)
1.2
1.0
No red tail
0.8
0.6
0.4
0.2
0
450
500
550 600 650
Wavelength (nm)
700
750
Reduced
photobleaching
All colors can be excited at one single wavelength
FIGURE 9.1
Influence of size on the optical properties of colloidal CdSe
[4]
.
