Gold nanoparticles for SERS

1. GOLD NANORODS AS SURFACE ENHANCED RAMAN ACTIVE
SUBSTRATES

2. What are nanoparticles?
• Nanoparticles can be defined as particles with
at least one of their three dimensional sizes in
the range of  1 nm -100 nm

3. •Bulk gold is a shiny, yellow noble metal.
•Good conductor
•Non-magnetic
•melts at 1,336 K.
•Inert.
•Nanoparticles of gold exhibit high chemical reactivity.
•Melting temperature decreases drastically as the sample size
goes down.
•Gold ceases to be noble
•Excellent catalysts
•Exhibit considerable magnetism.
•Insulators.
•Compounds made with gold inhibited the growth of bacteria.

4. Nanoparticles in ancient materials
Lycurgus Cup in the British Museum

5. What makes gold nanoparticles unique?
• Strong surface plasmon resonances.
(Top) Schematic drawing of the
interaction of an electromagnetic
radiation with a metal nanosphere. A
dipole is induced, which oscillates in
phase with the electric field of the
incoming light. (Bottom) Transverse and
longitudinal oscillation of electrons in a
metal nanorod.
SPR depends on the size, shape and dielectric constants of both the metal and
the surrounding material.

6. Application of gold nanoparticles
•Waveguides
•Catalysts
•Optical transmission
•Biomedical applications
•Information storage
•Optical limiters
•Sensors
•Surface enhanced Raman scattering (SERS) etc.

7. Synthesis of metal nanoparticles:
Bottom up method--assemble atoms to nanostructures
Top down method--cut into pieces in nanoscale

8. Top down (includes lithography) and Bottom up (includes colloidal synthesis)
approach
In the “bottom up” approach, gold nanoparticles have been chemically synthesized by
reducing gold precursors.
Bottom up approach produces nanostructures with less defects, more homogeneous
chemical composition.
Size and shape of NPs can be controlled

9. Synthesis of anisotropic metallic nanoparticles, especially gold
nanorods, have recently attracted a lot of attention due to their
distinctive optical properties.
Metal nanorods show two absorbance maxima corresponding to
the transverse surface plasmon resonance (TSPR) and longitudinal
surface plasmon resonance (LSPR) instead of a single absorption
maximum for the spherical Au dispersion.
These absorption peaks correspond to the electromagnetic wave
driven oscillation of the quasi-free electrons along and
perpendicular to the rods’ long axis. These two principle plasmon
absorption bands are tunable with the aspect ratio of the nanorods
through much of the visible and near-IR wavelength regime.

10. THANK YOU