PHYS01200704032 Debes Ray - Homi Bhabha National Institute

Chapter 1: Synthesis, Characterization and Applications of Gold Nanoparticles
Many applications became possible due to the large enhancement of the surface
electric field on the gold nanoparticles surface. The plasmon resonance absorption has an
absorption coefficient orders of magnitude larger than strongly absorbing dyes. Anisotropic
shapes have plasmon resonance absorptions that are even stronger, leading to increased
detection sensitivity. Gold nanoparticles generate enhanced electromagnetic fields that affect
the local environment. The field is determined by the geometry of the nanoparticle and can
enhance fluorescence of the metal itself, the Raman signal of a molecule on the surface, and
the scattering of light. The optical properties of noble gold nanoparticles lead to many uses as
sensing and imaging techniques. The use of DNA has been pioneered in assembling and
studying their interaction and their application in colorimetric detection of biological targets
based on the binding events of target DNA [23,24]. Also the use of gold nanoparticles in the
field of photonics is immense.
(ii) Electronic Properties
Gold nanoparticles, in particular, exhibit good chemical stability. In principle, they can be
surface functionalized with almost every type of electron-donating molecule including
biomolecules. Beyond that, in the meantime, several protocols have been developed that
allow their assembly into one, two and three dimensions. Altogether, these facts triggered the
development of concepts for the design of novel materials with very specific properties based
on the unique size-dependent properties of single nanoparticles and their collective properties
in assemblies, owing to dipolar, magnetic or electronic coupling. Single nanoparticles with
sizes in the range of a few nanometers exhibit an electronic structure that corresponds to an
intermediate electronic structure between the band structure of the bulk metal and the discrete
energy levels of molecules with a characteristic highest occupied molecular orbital (HOMO)–
lowest unoccupied molecular orbital (LUMO) gap [25].
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