Rice University laboratory has come up with a one-size-fits-almost-all
way to measure batches of single-walled nanotubes that promises to help
researchers and industry make more efficient use of the wondrous carbon
grown in a single batch can range in length from a few nanometers
(billionths of a meter) to thousands of nanometers. Until now, the only
practical method for measuring them was by imaging with an expensive
atomic force microscope (AFM).
with the new technique from the Rice lab of chemist Bruce Weisman,
revealed this month in the American Chemical Society journal ACS Nano,
researchers will be able to carry out these analyses more quickly and
with less manual labor.
end product is a histogram that shows the distribution of lengths in a
batch of nanotubes that, individually, are 50,000 times thinner than a
is just the kind of thing researchers want to know because, even at
that scale, the details loom large. When used to deliver strands of DNA
or drugs, for example, single-walled carbon nanotubes 200-300 nm long
seem easiest for cells to absorb. Other applications require longer
nanotubes, for example, in high-tech composite materials for aircraft
and spacecraft that need the strength and load transfer efficiency
offered by longer tubes.
Streit, a graduate student and lead author of the paper, spent two
years developing an experimental method and image-processing algorithm
able to pick out and track batches of nanotubes floating in solution in a
tiny well, about a millimeter across and a little less than two
The highly automated technique allows him to analyze batches of about 800 nanotubes in two hours.
main way to measure lengths until now has been with AFM,” he said. “For
that, you have to prepare a sample, look at it under a microscope, make
sure that contaminants have been removed, record images and then
measure the lengths. It can take hours and hours for most workers.”
new process, called length analysis by nanotube diffusion (LAND), is
much simpler. Although it only observes semiconducting single-walled
nanotubes, which are naturally fluorescent at near-infrared wavelengths,
it should help researchers simplify the characterization of nanotube
lengths have different utilities and functions in applications,” said
Weisman, a professor of chemistry and a pioneer in the science of
nanotube fluorescence. “Some applications need a certain short length,
while there are others where longer is better. And currently, nanotube
length distributions are poorly controlled.
one goal is to get more control over the lengths of your nanotubes, and
to do that you need to develop separation methods. To develop
separation methods, you need good characterization tools.”
Sergei Bachilo, a research scientist at Rice, compared the need for
different-size nanotubes to a shoe store, where one size definitely does
not fit all. “It wouldn’t work very well if the store only had shoes in
the average size,” he said.
dust in a shaft of light, nanotubes in a liquid environment move around
due to Brownian motion. It’s that inherent movement that reveals their
lengths. So Streit takes video. The resulting movies look like a field
of stars blinking and wandering in the night sky, but from those frames
he is able to extract trajectories that tell him how long each
individually tracked nanotube is. The software also automatically
compiles the statistical data to make the histogram.
special computations are necessary to account for nanotubes that show
“fragmented trajectories,” when a tube disappears behind another or
leaves the field of view for a few frames.
shorter nanotubes (below a few dozen nanometers in length) are hard to
capture on video. “They’re dimmer, and they move faster, so sometimes
they’re just a blur,” Weisman said. “One of the tricks Jason uses is to
make the liquid in which they’re moving more viscous” simply by adding a
special sugar. “That slows them down enough to give us a better view.
hope that this will be a valuable tool for basic and applied research,”
Weisman said. “Right in our laboratory, we’re already doing basic photophysical studies in which this method plays a crucial part.
that are slow and cumbersome just don’t get used,” he said. “That’s
simply the truth. And when you convert to a method that’s fast and easy,
people will use it a lot more. It not only speeds things up, it leads
scientists into activities they never would have undertaken before.
is going to be an important method for a lot of what we do around here,
and hopefully for other labs as well,” Weisman said.
paper’s co-authors include Anton Naumov of Ensysce Biosciences, who
earned his doctorate at Rice in 2011 and has a complimentary appointment
to the university; and Constantine Khripin and Ming Zheng of the
polymers division of the National Institute of Standards and Technology.
The research was supported by the Welch Foundation and the National Science Foundation.
Source: Rice University