Chemistry Reference
In-Depth Information
Light
Electron cloud
oscillation
Electron-phonon
coupling
Lattice
expansion
Hot electron
distribution
Hot
particle
Resonant
vibrational motion
Figure 9.7
Interaction of light with metallic nanoparticles. Light absorption heats
the electrons of the particles, which then equilibrate through electron-phonon cou-
pling. This initiates coherent vibrational motion in the particles called surface plasmon
resonance. The heat created can then be transferred to its surroundings through
transduction. [Adapted from Hartland (2007) with permission from Macmillan
Publishers Ltd.]
can induce bond cleavage, phase transitions, or mechanical damage to biologi-
cal systems. In recent times, there has been a fl urry of research into the optical
properties and potential applications of metallic nanoparticles. Metallic
nanoparticles (mainly gold but also silver and copper) are of interest as on
exposure to radiation of a specifi c wavelength and intensity, can heat NPs to
their vaporization point within femtoseconds due to the activation of surface
plasmon resonances, a phenomenon demonstrated in Figure 9.7 (Govorov and
Richardson, 2007; Murray and Barnes, 2007). Wavelengths at which the NPs
absorb is tuneable according to their size, shape, composition, and state of
aggregation (Jain et al., 2006; Volodkin et al., 2009). The use of spheres, rods,
and shells has been reported. The wavelengths at which the NP absorb are
usually in the NIR region, wavelengths not signifi cantly absorbed by cellular
material. In addition to their specifi c dimensions, metallic nanoparticles can
also be functionalized and made more biocompatible through the facile
binding of various types of biomolecules, for example, phosphatidylcholine
(Takahashi et al., 2006 ).
Therapeutic applications of current research has focused on the use of
metallic nanoparticles to cause tumor cell death by localized heating of the
tumor (Dickerson et al., 2008; Lee et al., 2009b; Maeda et al., 2003; Tong et al.,
2007) or to elicit remote release of entrapped materials via photothermal
conversion (Skirtach et al., 2005) from within liposomes (Paasonen et al., 2007;
Park et al., 2006; Troutman et al., 2009; Volodkin et al., 2009; Wu et al., 2008),
polyelectrolyte capsules (Munoz et al., 2008), hydrogels (Das et al., 2007, 2008;
Kim and Lee, 2006), polymer vesicles (Murphy and Orendorff, 2005), or from
a NP-drug conjugate (Agasti et al., 2009; Barhoumi et al., 2009). Plasmon
resonant heating has also been used to trigger phase transitions in self-
assembled lipid systems with a view to elucidate the mechanisms behind
photothermal activated responses (Orendorff et al., 2009; Urban et al., 2009;
Yaghmur et al., 2010). Recently, we have shown that incorporation of hydro-
phobized gold nanorods can be utilized to switch liquid crystalline structure
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