Artist’s concept of nanotubes on the liquid surface. Image: Los Alamos National Laboratory |
Many
physical and chemical processes necessary for biology and chemistry occur at
the interface of water and solid surfaces. Researchers at Los Alamos National
Laboratory (LANL), publishing in Nature
Nanotechnology, have now shown that semiconducting carbon nanotubes—light
emitting cylinders of pure carbon—have the potential to detect and track single
molecules in water.
Using
high-speed microscopic imaging, they found that nanotubes could both detect and
track the motion of individual molecules as they bombard the surface at the
water interface. Traditional techniques to investigate molecules on surfaces
cannot be used in water because the study requires low-pressure atmospheres
such as one finds in space. The team is hopeful that their work will lead to
practical, nanotube-based, single-molecule detectors in aqueous biological and
chemical environments.
Molecular
motion and attachment to surfaces is important for driving chemistry that
ranges from the production of ammonia on metal to the enzymatic oxidation of
glucose. The attachment takes place through sporadic motion followed by a
collision with the surface to which the molecule sticks. Molecules can then
move along the surface where they can collide with other molecules and undergo
chemical reactions.
In
traditional “surface science” experiments these processes are imaged in a
vacuum where other molecular species from the air cannot blur the image. In
solutions such as water, there has been no way to do this directly.
Consequently, researchers have been searching for a material that can be used
in water to detect individual molecules for surface-science applications.
Inspired
by this challenge, a team of Los Alamos
scientists (Jared Crochet, Juan Duque, Jim Werner, and Steve Doorn) at LANL’s
Center for Integrated Nanotechnologies explored using light-emitting carbon
nanotubes as detectors. With techniques developed by others, the team used soap
and water to stabilize the nanotubes where they could be imaged directly with a
high-speed video camera. When illuminated with laser light these tubes shine
brightly, like long glow sticks.
When
the glowing nanotubes are exposed in water to different chemicals, the
researchers saw that certain spots of the tube would briefly go dim as the
molecules bombarded the surface. This allowed them to determine how effectively
certain molecules would stick to the surface. The researchers were also able to
track the motion of molecules as they moved along the surface. The team is now
examining how chemical reactions proceed on nanotube surfaces to better
understand chemistry at the water interface for biological and chemical
applications.
