Biomedical Engineering Reference
In-Depth Information
properties are well-understood in the framework of classical Mie theory. The
plasmon resonance of spherical nano-gold in aqueous environment is found
within 500-600 nm, almost independent of geometrical volume [102].
Because of absorption in the visible, conventional nano-gold is not regarded
as a candidate ideal chromophore for laser-welding of biological tissues. Lo-
calization of power deposition requires preferential use of near-infrared radia-
tion. Theoretical calculations based on different approaches (including Gans
theory [102], dipolar approximations [102, 105], or hybridisation of Mie reso-
nances [111]) agree on the possibility to steer the absorption of nano-gold to
well within the near-infrared by introduction of nonspherical morphologies.
The experimental synthesis of gold nanoparticles with unconventional shape
is a very active field of research [112]. By intrusive modification of existing
procedures for spherical nano-gold, a number of nonspherical gold nanopar-
ticles have been demonstrated, including dielectric-core/metal-shell silica or
gold-sulphide/gold nano-shells [113-115], complex hollow shells as gold nano-
cages [116], or high aspect ratio gold nano-rods [106, 117, 118]. Tuning of size
and shape of these nanoparticles allows for tuning of plasmon resonances
in good agreement with theoretical calculations. In particular, absorption
within the near-infrared range of interest is becoming a mature achievement.
Near-infrared-light irradiation of biological media dispersed with nonspheri-
cal nano-gold was proven to result in selective, controllable, and significant
heating [119, 120].
Photo-activated nonspherical nano-gold holds the promise of manifold ap-
plications in the emerging field of nano-medicine. Proposals of extreme interest
are e.g., in the treatment of tumors by selective ablation of individual malig-
nant cells [120-122]. In our context, the potential of silica/gold nano-shells in
the laser welding of tissues has recently been demonstrated in combination
with an albumin solder [99]. Absorption of 820 nm diode laser radiation by a
low concentration of nano-shells was shown to induce successfully the coagu-
lation of albumin proteins and the ensuing soldering of muscles ex vivo and
of skin in vivo (rat model). Preliminary results are very promising. However,
much progress is still required. We estimate that future innovation will take
special advantage of the adaptable functionalization of nano-gold. This may
for example enable the selective targeting of individual biological structures,
which may in turn result in the engineering of tissue power absorption pro-
files with resolution in the nano-range. This is a completely novel and powerful
perspective in the laser-welding of biological tissues.
Currently, the replacement of traditional organic molecules with nanos-
tructured chromophores is an inspiring possibility, which is yet far from the
clinical application. As a very recent concept and technology, there exists at
present basically no experimental evidence of the superiority of these new
materials in the welding of tissues. Additional aspects of practical concern
include their biocompatibility and overall sustainability (e.g., economical). In
short, nano-medicine is a broad and thriving context, offering a wealth of
