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October 14, 2008: A team of researchers at Northwestern
U. has demonstrated the ability to rapidly write nanoscale
protein arrays using a tool they call the nanofountain probe (NFP).
"The NFP works much like a fountain pen, only on a much smaller scale, and in
this case, the ink is the protein solution," said Horacio Espinosa,
head of the research team and professor of mechanical engineering in
the McCormick School of Engineering and Applied Science at
Northwestern.
The results, which will be published online the week of Oct. 13
in the Proceedings of the National Academy of Sciences
(PNAS), include demonstrations of sub-100nm protein dots and
sub-200nm line arrays written using the NFP at rates as high as
80μm/second.
Each nanofountain probe chip has a set of ink reservoirs that
hold the solution to be patterned. Like a fountain pen, the ink is
transported to sharp writing probes through a series of
microchannels and deposited on the substrate in liquid form.
"This is important for a number of reasons," said Owen Loh, a
graduate student at Northwestern who co-authored the paper with
fellow student Andrea Ho. "By maintaining the sensitive proteins in
a liquid buffer, their biological function is less likely to be
affected. This also means we can write for extended periods over
large areas without replenishing the ink."
Earlier demonstrations of the NFP by the Northwestern team
included directly writing organic and inorganic materials on a
number of different substrates. These included suspensions of gold
nanoparticles, thiols, and DNA patterned on metallic- and
silicon-based substrates.
In the case of protein deposition, the team found that by
applying an electrical field between the nanofountain probe and
substrate, they could control the transport of protein to the
substrate. Without the use of electric fields, protein deposition
was relatively slow and sporadic. However, with proper electrical
bias, protein dot and line arrays could be deposited at extremely
high rates.
"The use of electric fields allows an additional degree of
control," Espinosa said. "We were able to create dot and line arrays
with a combination of speed and resolution not possible using other
techniques."
Espinosa collaborated closely with Neelesh Patankar, associate
professor of mechanical engineering at Northwestern, and Punit
Kohli, assistant professor of chemistry and biochemistry at Southern
Illinois University, Carbondale.
"We are very excited by these results," said Espinosa. "This
technique is very broadly applicable, and we are pursuing it on a
number of fronts." These include single-cell biological studies and
direct-write fabrication of large-scale arrays of nanoelectrical and
nanoelectromechanical devices.
"The fact that we can batch fabricate large arrays of these
fountain probes means we can directly write large numbers of
features in parallel," added Espinosa. "The demonstration of rapid
protein deposition rates further supports our efforts in producing a
large-scale nanomanufacturing tool."
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