Biomedical Engineering Reference
In-Depth Information
fl uorescent dye materials. Quantum dots are ~20 times brighter than the typical organic
dye molecules, and their emission is ~100 times more stable to photobleaching than
conventional fl uorescent dyes (e.g., rhodamine). They can be made water soluble
by chemical functionalization and can also be made specifi c cell- or organ-targetable via
chemical or biological conjugation (Chan and Nie
1998
; Akerman
2002
) . They can be
imaged with a conventional fl uorescence microscope. Besides the visible-emitting
quantum dots, both near-IR and UV-emitting dots can also be synthesized.
The essence of bottom-up processing of nanotechnologies is mastered by nature
in biological systems. For example, cells function on similar length scales to those
of synthetic nanosystems. The molecules that operate and react in living cells are
similar to the devices imagined for building nanosystems. Rather than using bio-
logical elements for the assembling of inorganic nanostructures, another way pro-
posed for the synthesis of nanomaterials relies on incorporating the biological
components themselves into artifi cial nanoscale structures and devices. Biological
molecular motors, for example, have been incorporated into artifi cial structures, and
the light harvesting complexes of plants or photosynthetic bacteria have been incor-
porated into synthetic membranes. From this point on, a vast array of applications
that combine artifi cial structures with biological components can be envisioned and
investigated, defi ning the future of nanobiotechnology.
1.2.4
Laser Pyrolysis
Laser pyrolysis is a technique that uses IR laser energy to decompose materials by
heating gas-phase reactants in an oxygen-deprived environment. This method is
used to produce extremely pure spherical nanoparticles with small-diameter, small-
size distribution and with a low agglomeration level (Herlin-Boime et al.
2004
) .
Such particles are used, for example, as precursors for surface treatments of ceram-
ics. A similar technique, called laser ablation, is also used for the production of
CNTs and nanowires.
1.2.5
Electrochemical Deposition/Electroplating
Electrochemical deposition is a technique used for manufacturing ordered arrays of
nanomaterials, like quantum dots on a fl at surface, for coating different surfaces or
for patterning thin fi lms (Allred et al.
2005
). It represents one of the most powerful
techniques that allow obtaining high-density and high-aspect ratio designs, with
excellent reproducibility of the process and with great precision of the fi nal prod-
ucts. Similarly to lithographic techniques, electrochemical deposition requires a
polymer mask through which metal is deposited. Differently from other mask-based
techniques like isotropic etching, ion milling, and RIE, electrochemical deposition
avoids the problem of shadowing near edges or interfaces and builds structures
atom by atom. The techniques rely on the presence of an electric fi eld in a solution,
which allows metal ions to discharge and conform to the smallest features of a mold.
