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some of the first work documenting the uptake of carbon
nanotubes by living cells, a team of chemists and life
scientists from Rice University and the University of
Texas Health Science Center and Houston's Texas Heart
Institute have selectively detected low concentrations
of nanotubes in laboratory cell cultures.
The research appears in the
Dec. 8 issue of the Journal of the American Chemical
Society. It suggests that the white blood cells, which
were incubated in dilute solutions of nanotubes, treated
the nanotubes as they would other extracellular particles
– actively ingesting them and sealing them off inside
chambers known as phagosomes.
“Our goal in doing the experiment
was both to learn how the biological function of the
cells was affected by the nanotubes and to see if
the fluorescent properties of the nanotubes would
change inside a living cell,” said lead researcher
Bruce Weisman, professor of chemistry at Rice. “On
the first point, we found no adverse effects on the
cells, and on the second, we found that the nanotubes
retained their unique optical properties, which allowed
us to use a specialized microscope tuned to the near-infrared
to pinpoint their locations within the cells.”
The research builds upon Weisman's
groundbreaking 2002 discovery that each of the dozens
of varieties of semiconducting, single-walled carbon
nanotubes (SWNTs) emits its own unique fluorescent
signature.
The new findings suggest that
SWNTs might be valuable biological imaging agents,
in part because SWNTs fluoresce in the near-infrared
portion of the spectrum, at wavelengths not normally
emitted by biological tissues. This may allow light
from even a handful of nanotubes to be selectively
detected from within the body.
Carbon nanotubes are cylinders
of carbon atoms that measure about one nanometer,
or one-billionth of a meter, in diameter. They are
larger than a molecule of water, but are about 10,000
times smaller than a white blood cell.
The latest tests bode well
on two counts. Not only did the nanotubes retain their
optical signatures after entering the white blood
cells, but the introduction of nanotubes caused no
measurable change in cell properties like shape, rate
of growth or the ability to adhere to surfaces.
In conducting the tests, Weisman
was joined by colleagues Paul Cherukuri and Silvio
Litovsky, both of the University of Texas Health Science
Center at Houston's Texas Heart Institute, and Sergei
Bachilo of Rice. The researchers cultured mouse macrophage
cells in solutions containing between zero and 7 parts-per-million
carbon nanotubes for periods of up to 96 hours. They
found that the amount of carbon nanotubes taken up
by the cells increased smoothly as the concentration
or the time of exposure increased. In addition, some
cultures were run at cooler temperatures and showed
a slower rate of uptake, a finding that suggested
that the nanotubes were being ingested through normal
phagocytosis.
The samples were studied using
a spectrofluorometer and a fluorescence microscope
that was modified for near-IR imaging through the
addition of a digital camera containing indium gallium
arsenide detector elements.
Although long term studies
on toxicity and biodistributions must be completed
before nanotubes can be used in medical tests, the
new findings indicate nanotubes could soon be useful
as imaging markers in laboratory in vitro studies,
particularly in cases where the bleaching, toxicity
and degradation of more traditional markers are problematic.
The research was funded by
the National Science Foundation, the Welch Foundation,
the United States Army, Rice's Center for Biological
and Environmental Nanotechnology and Rice's Center
for Nanoscale Science and Technology.
CONTACT: Jade Boyd
PHONE: (713) 348-6778
E-MAIL: jadeboyd@rice.edu
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