February 19,
2007
Super-thin filter opens possibility for better
dialysis, fuel cells, and more
At only 50-atoms thick and 4,000 times thinner than a
human hair, a newly designed porous membrane could revolutionize the way
doctors and scientists manipulate objects as small as a molecule. The
filter, developed by a team of researchers at the University, is so thin
it’s invisible edge-on and can withstand surprisingly high pressures.
Nanofilter arrary: four-inch wafer with 160 membranes
The new design, featured in the February 15 issue of
the journal Nature, could be key to better separation of blood proteins for dialysis
patients, speeding ion exchange in fuel cells, creating a new environment
for growing neurological stem cells, and purifying air and water in
hospitals and clean-rooms at the nanoscopic level.
“It’s amazing, we have a material as thin
as some of the molecules it’s sorting, and even riddled with holes,
but can withstand enough pressure to make real-world nanofiltering a
practical reality,” says research associate Christopher Striemer,
cocreator of the membrane. “That ultra-thinness means much higher
efficiency and lower sample loss, so we can do things that can’t
normally be done with current materials.”
The membrane is a 15-nanometer-thick slice of the same
silicon that’s used every day in computer-chip manufacturing. In the
lab of Philippe Fauchet, professor of electrical and computer engineering,
Striemer discovered the membrane as he was looking for a way to better
understand how silicon crystallizes when heated.
He found that as parts of the silicon contracted into
crystals, holes opened up in their wakes. Imagine a party of people spread
out evenly throughout a room, but as the evening progresses and people
huddle into cliques, scattered areas of empty floor open up.
In talks with Striemer and Fauchet, James McGrath,
assistant professor of biomedical engineering, and his graduate student Tom
Gaborski realized that since the membrane’s holes were only
nanometers in size, it might be possible to separate objects as small as
proteins much more effectively than is being done now.
While the filter seemed promising, McGrath knew
they would need to verify the predictions. “When you build something
at this scale, you’re closing in on the quantum world and you never
know what the properties are going to be,” he says.
When Striemer tested his design, he found that the same
50-atom thickness could hold back an astonishing 15 pounds per square inch
of pressure.
And as if filtering by nanoscale size weren’t
enough, the Rochester team has found a way for the nanofilter to carry a
fixed charge, effectively making the hole “smaller” for
molecules of a certain charge than for others. In a single filter,
it’s now possible to quickly and easily separate molecules by their
size and their charge—a serious boon for fuel cell researchers, who
wish to move only certain ions from one part of a fuel cell to another.
Separating molecules by size and charge efficiently
also is the goal of kidney dialysis researchers. Johnson & Johnson
recently gave the Rochester team a $100,000 grant to pursue developing the
membrane’s use in separating blood proteins with the hope of creating
a more efficient method of dialysis.
The Rochester group sees many more applications for the
membrane in the future. One of the most intriguing ideas is that it may
play a role in growing neurons from stem cells.
Steve Goldman, Glenn-Zutes Chair in Biology of the
Aging Brain and professor of neurology, discussed the technology with
McGrath and colleagues and was impressed. “It’s a spectacularly
interesting technology, that opens a realm of new possibilities in fields
as diverse as organ reconstitution, proteomics and microfluidics,”
says Goldman. “Its potential applications to neuroscience, cell
biology and medical research may be profound.”
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