Chemistry Reference
In-Depth Information
4.3.3 Photothermal Agents
The light-absorbing properties of gold nanoparticles make them effective heat-
mediating transmitters. The absorbed light energy is dissipated to surrounding
molecules and thereby elevating the temperature of the surrounding area. This
effect may be used to open polymer microcapsules for drug delivery purposes.
Near-IR absorbing gold nanoparticles (including gold nanoshells and nanorods)
rapidly produce heat when excited by light at wavelengths from 700 to 800 nm.
This property has been used to kill targeted tumour cells (hyperthermia or photo-
dynamic therapy). The emergence of gold nanoparticles in this application arises
because of their unique photophysical properties which make them very suitable for
cancer phototherapy. The plasmon surface resonance results in visible and near-
infrared light absorption several orders of magnitude more intense than that of
conventional phototherapy cancer agents. Huang et al. have recently reviewed
plasmonic photothermal therapy (PPTT) in the treatment of malignant tumours
[
182
]. In addition appropriately functionalised nanoparticles may be designed to
bind specifically to certain cells and thereby target and destroy malignant cells.
The potential cytotoxicity of the nanoparticles is a side effect which cannot be
ignored [
183
]. Gold nanoparticles (2-4 nm) stabilised by a phthalocyanine
(Pc) photosensitiser and a phase-transfer agent have been shown to form a three-
component system to generate singlet oxygen with enhanced quantum yields
compared to the free Pc. Additionally, the association of the transfer reagent
promoted the solubility of the surface-bound hydrophobic sensitiser in polar sol-
vents which would facilitate their systemic injection [
184
]. The results demonstrate
a potentially useful vehicle for the delivery of photosensitiser agents in photo-
dynamic therapy.
4.4 Nanoelectronics and Optics
Gold nanoparticles have been used in a wide range of applications in the electronics
industry and particularly as conductors in printable inks and electronic chips.
Nanoscale gold nanoparticles are being used to connect resistors, conductors and
other elements to electronic chips. As the goal of producing even smaller electronic
devices is achieved, nanoparticles become potentially more important components
in chip design [
185
]. In addition to miniaturisation the distances between transistors
and related switching elements on a chip get shorter and quantum effects become
relevant. Today's nano-lithographic fabrication techniques allow scaling down to
50 nm or below [
186
]. This has already made a great impact on the performance of
traditional semiconductor circuits, and it opens up new opportunities utilising
quantum effects. Following the utilisation of charging effects, the so-called Cou-
lomb effects, in metallic circuits which are based on tunnel junctions with submi-
cron sizes, individual charge carriers become a realistic possibility [
187
]. Potential
developments in this field, described as single electronics [
187
], have recently been
