Researchers have demonstrated a new imaging tool for tracking structures called single-wall carbon nanotubes in living cells and the bloodstream, work that could aid efforts to perfect their use in laboratory or medical applications. Here, the imaging system detects both metallic and semiconducting nanotubes, false-colored in red and green, in live hamster cells. Image: Weldon School of Biomedical Engineering, Purdue University |
Researchers have demonstrated a new imaging tool for
tracking structures called carbon nanotubes in living cells and the
bloodstream, which could aid efforts to perfect their use in biomedical research
and clinical medicine.
The structures have potential applications in drug
delivery to treat diseases and imaging for cancer research. Two types of
nanotubes are created in the manufacturing process, metallic and
semiconducting. Until now, however, there has been no technique to see both
types in living cells and the bloodstream, says Ji-Xin Cheng, an associate
professor of biomedical engineering and chemistry at Purdue University.
The imaging technique, called transient absorption, uses a
pulsing near-infrared laser to deposit energy into the nanotubes, which then
are probed by a second near-infrared laser.
The researchers have overcome key obstacles in using the
imaging technology, detecting and monitoring the nanotubes in live cells and
laboratory mice, Cheng says.
“Because we can do this at high speed, we can see
what’s happening in real time as the nanotubes are circulating in the
bloodstream,” he says.
Findings are detailed in a research paper posted online in
Nature Nanotechnology.
The imaging technique is “label free,” meaning
it does not require that the nanotubes be marked with dyes, making it
potentially practical for research and medicine, Cheng says.
“It’s a fundamental tool for research that will
provide information for the scientific community to learn how to perfect the
use of nanotubes for biomedical and clinical applications,” he says.
The conventional imaging method uses luminescence, which
is limited because it detects the semiconducting nanotubes but not the metallic
ones.
The nanotubes have a diameter of about 1 nm, or roughly
the length of 10 hydrogen atoms strung together, making them far too small to
be seen with a conventional light microscope. One challenge in using the
transient absorption imaging system for living cells was to eliminate the
interference caused by the background glow of red blood cells, which is
brighter than the nanotubes.
The researchers solved this problem by separating the
signals from red blood cells and nanotubes in two separate
“channels.” Light from the red blood cells is slightly delayed
compared to light emitted by the nanotubes. The two types of signals are
“phase separated” by restricting them to different channels based on
this delay.
Researchers used the technique to see nanotubes
circulating in the blood vessels of mice earlobes.
“This is important for drug delivery because you want
to know how long nanotubes remain in blood vessels after they are
injected,” Cheng says. “So you need to visualize them in real time
circulating in the bloodstream.”
The structures, called single-wall carbon nanotubes, are
formed by rolling up a one-atom-thick layer of graphite called graphene. The
nanotubes are inherently hydrophobic, so some of the nanotubes used in the
study were coated with DNA to make them water-soluble, which is required for
them to be transported in the bloodstream and into cells.
The researchers also have taken images of nanotubes in the
liver and other organs to study their distribution in mice, and they are using
the imaging technique to study other nanomaterials such as graphene.
