RIDGE, Tenn., July 14, 2004 -- A technology with proven
environmental, forensics and medical applications
has received a shot in the arm because of an invention
by researchers at the Department of Energy's Oak Ridge
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
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
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 is provided by
DOE's Office of Biological and Environmental Research
and the Laboratory Directed Research and Development
Contact: Ron Walli
DOE/Oak Ridge National Laboratory