CHESTNUT HILL, MA (5-23-05) -- Researchers in the laboratory of Boston College
Chemistry Professor John T. Fourkas have demonstrated that gold particles comparable
in size to a molecule can be induced to emit light so strongly that it is readily
possible to observe a single nanoparticle. Fourkas, in collaboration with postdoctoral
researcher Richard Farrer and BC undergraduates Francis Butterfield and Vincent
Chen, coaxed the particles into strong emission of visible light using a technique
called multiphoton absorption induced luminescence (MAIL).
The most efficient gold nanoparticles could be observed
at laser intensities lower than those commonly used
for multiphoton imaging, in which specific tissues
or cells -- cancer cells, for example -- are fluorescently-labeled
using special stains that enable them to be studied.
"One of the most exciting aspects of this technique
is that it paves the way for being able to observe
behavior in living tissues at the single molecule
level," said Fourkas. "The fluorescent molecules
commonly used in multiphoton imaging give out only
a limited amount of light, 'burn out' quickly under
continuous observation, and are prone to blinking
on and off.
"The gold particles, however, do not blink or burn
out, even after hours of observation, and the brightest
ones emit much more light than do molecules," he
said. "We now have the ability to see single nanoparticles
under conditions where people usually look at thousands
or millions of stain molecules. This could allow
us, for instance, to track a single molecule of a
drug in a cell or other biological sample."
Other advantages of the technique are that the gold
particles can be prepared easily, have very low toxicity,
and can readily be attached to molecules of biological
interest, said Fourkas. In addition, the laser light
used to visualize the particles is at a wavelength
range that causes only minimal damage to most biological
The findings will be published in the June issue
of Nano Letters.