PHYS01200704032 Debes Ray - Homi Bhabha National Institute

Chapter 1: Synthesis, Characterization and Applications of Gold Nanoparticles
properties of gold nanoparticles. Due to their small size, gold particle-based sensors could
have an important impact in diagnostics [78].
The plasmon resonance frequency is a very reliable intrinsic feature present in gold
nanoparticles (with wavelengths around 510–530 nm for Au nanoparticles of around 4–40 nm
diameter) that can be used for sensing [79]. The binding of molecules to the particle surface
can change the Plasmon resonance frequency directly, which will lead to a change in the
color of the solution. Besides the detection of analytes, such colour changes can also be used
to measure lengths. The concept of such „rulers on the nanometer scale‟ is again based on
colour changes of gold particles if the gold particles are in close proximity. Different sites of
a macromolecule can be linked to gold particles. By observing the colour of the gold particles
the distance between these sites can be measured and in this way for example conformation
changes in molecules can be observed [80,81].
1.5.2. Nanoelectronics
According to the present paradigm of electronic information storage and exchange,
continuous miniaturization of microelectronic devices turns out to be the only evident
concept for improving the performance of integrated circuits. One of the most promising
concepts is the development of single-electron (SE) devices which retain their scalability
down to the molecular level [8,82]. At present, due to exploitation of charging effects or socalled
Coulomb effects in metallic single-electron devices comprising tunnel junctions with
sub-micrometer size, individual charge carriers can be handled. The discreteness of the
electric charge becomes essential and the tunneling of electrons in a system (SET) of such
junctions can be affected by the Coulomb interaction of electrons which can be varied by an
externally applied voltage or by injected charges. The simplest arrangement for a twoterminal
device is a metal island between two metallic electrodes separated from each other
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