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ARBOR, Mich.---Our eyes may become more than windows
of the soul if a multidisciplinary team of University
of Michigan researchers succeeds with a clever combination
of nanoparticles and ultrafast pulsed laser to see individual
cells as they zip past in the bloodstream.
The U-M team of physicians,
scientists and engineers has $3 million from NASA
to determine a way of detecting radiation exposure
on the fly by looking for individual cells that have
been harmed. Now, such cell counting is only achieved
by drawing blood and using an expensive machine called
a cytometer, operated by a skilled lab technician.
A certain amount of cell death
is normal and expected, so there would always be some
background fluorescence. What the researchers are
looking for is a sudden increase in the population
of dead white blood cells, which is one of the calling
cards of radiation poisoning.
NASA is particularly concerned
with radiation exposure as one of the leading health
risks in long-term space travel. Radiation---sub-atomic
particles moving at tremendous speeds---careens in
all directions in space. It can kill cells and damage
the DNA within them, causing long-term health problems,
especially cancers.
Individual cells in the bloodstream
are tagged with a nanoparticle called a dendrimer
that is much smaller than a blood cell. It's a synthetic
that is grown in layers of branching molecules that
resemble a tree. At the tips of these branches on
the dendrimer, scientists can attach biomolecules
that have specific affinity for the white blood cells.
Other arms of the dendrimer carry a fluorescent material
that will light up on cue if the white blood cell
dies.
The idea of using dendrimers
for real-time cell counting came from Dr. James R.
Baker Jr., the Ruth Dow Doan Professor of Biologic
Nanotechnology and director of U-M's Center for Biologic
Nanotechnology. His research group is also exploring
the use of dendrimers for drug delivery and improved
medical imaging.
To see cells as they flow,
the researchers are using a pulsed laser developed
by physicist Theodore Norris of the U-M's Center for
Ultrafast Optical Science that can be focused down
to a spot smaller than a cell. "Jim (Baker) was
wondering about cytometry in vivo, and we came in
with a photonic solution," Norris said.
The spot-focused laser allows
researchers to watch a capillary blood vessel just
a few blood cells in diameter and to count individual
spots of fluorescence as they zip past. The focal
area of the near-infrared laser is so tight that they
can be sure that each flash of fluorescence represents
just a single cell, said Norris, professor of electrical
engineering and applied physics.
"This could be used for
more than just radiation exposure," Baker said.
"We should be able to continually monitor cell
death from whatever cause."
On Earth, we are protected
from most of this space radiation by the planet's
magnetic field and by the thickness of the planet
itself beneath our feet. But away from the Earth,
astronauts will have only the vehicle around them
and their clothing to shield them.
It is estimated that a 2-1/2-year
mission to Mars could expose an astronaut to the lifetime
dose of radiation allowed by NASA. An intense solar
flare during the journey could even deliver a fatal
dose of radiation in a single burst.
"NASA has told us that
the trip to Mars could be one-way," Norris said.
"Still, they've got people who are willing to
do it."
U-M studies on living mice
have shined the light through their semi-translucent
ears to see the fluorescing dendrimers within capillaries.
The proposal to NASA was for using the capillaries
on the retina at the back of the eye, but human ears
might work just as well. "We just need to see
a capillary," Norris said. "It doesn't have
to be in the eye."
For more information, visit:
http://www.umnbei.umich.edu/
For more on Baker, visit: http://ipumich.temppublish.com/public/experts/ExpDisplay.php?ExpID=945
For more on Norris, visit:
http://www.eecs.umich.edu/OSL/Norris/
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