Nanoprobe creates world of new possibilities

OAK RIDGE, Tenn - ORNL's
nanoprobe, which is based on a light scattering technique, can detect
and analyze chemicals, explosives, drugs and more at a theoretical
single-molecule level. This capability makes it far more selective and
accurate than conventional competing technologies.

The
probe is an optical fiber tapered to a tip measuring 100 nanometers
with an extremely thin coating of nanoparticles of silver, which
induces the surface-enhanced Raman scattering (SERS) effect. Normally,
when a sample is illuminated by a laser beam, there is a small
reflection of light, known as Raman scattering. The light shows
vibration energies, which are unique to each compound, and that
information allows scientists to identify the substance.

With
the SERS nanoprobe, the laser light creates rapid oscillations of the
electrons in the silver nanoparticles, which produce an enormous
electromagnetic field that contributes to increase the Raman scattering
signal. The ORNL nanoprobe works with any surface to induce the SERS
effect.

"The
significance of this work is that we are now able to perform direct
analysis of samples -- even dry samples -- with no preparation of the
surface," said ORNL's Tuan Vo-Dinh, who leads a team that developed the
nanoprobe. "Also, the small scale of the nanoprobe demonstrates the
potential for detection in nanoscale environments, such as at the
intracellular level."

Ordinarily,
surface-enhanced Raman scattering analysis of samples on a surface
requires modification or treatment of the sample. This may consist of
physically removing the sample and diluting it in a liquid containing
silver nanoparticles; however, this practice is unnecessary with the
ORNL nanoprobe.

Vo-Dinh
and Life Sciences Division colleagues David Stokes and Zhenhuan Chi
experimented with nanoprobes made of several materials of varying
thickness. They settled on silver-island films because they are easier
to reproduce than silver-coated particles and they form only a thin
coating, which helps maintain the nanoscale diameter of the tapered
tip.

The
development of the SERS nanoprobe could lead to increasing interest in
SERS as an ultra-sensitive detection tool, allowing direct analysis of
samples for a wide variety of applications, Vo-Dinh said. These
applications range from environmental monitoring to intracellular
sensing and medical diagnostics.

ORNL
is managed by UT-Battelle for the Department of Energy. Funding for the
project was provided by DOE's Office of Biological and Environmental
Research and the Laboratory Directed Research and Development program.

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