VA—Duke University engineers have demonstrated that
enzymes can be used to create nanoscale patterns on
a gold surface. Since many enzymes are already commercially
available and well characterized, the potential for
writing with enzyme "ink" represents an
important advance in nanomanufacturing.
This research was funded by the National Science Foundation
through a Nanotechnology Interdisciplinary Research
Initiative (NIRT) grant.
Enzymes are nature's catalysts -- proteins that stimulate
chemical reactions in the body and are used in a wide
range of industrial processes, from wastewater treatment
to cheese making to dissolving blood clots after heart
In their experiments, the engineers used an enzyme
called DNase I as an "ink" in a process
called dip-pen nanolithography -- a technique for
etching or writing at the nanoscale level. The dip-pen
allowed them to inscribe precise stripes of DNase
I ink on a gold plate, which they had previously coated
with a thick forest of short DNA strands. The stripes
of the enzyme were 100 nanometers wide -- about one-millionth
the diameter of a human hair.
Once the researchers had created the stripes, they
then activated the enzyme with a magnesium-containing
solution. This changed the DNase I into a form that
efficiently breaks down any DNA in its path. As a
result, the team reports in the May 2004, issue of
the Journal of the American Chemical Society, available
online as of March 27, 2004, the stripes of activated
enzyme carved out 400 nm-wide "troughs"
in the DNA coating.
"We were surprised that the enzyme 'ink' worked
so well, because it was simply deposited on the surface
and could have washed away during the processing steps,"
says biomedical engineer Ashutosh Chilkoti of Duke's
Pratt School of Engineering, who leads the project.
Chilkoti credits much of the experiment's success
to the laboratory skills of Jinho Hyun, who was a
post-doctoral fellow in his group, and who is now
an assistant professor at Seoul National University.
But this experiment was also an important proof of
principle, says Chilkoti: until now, few researchers
have explored biological substances for nanoscale
manufacturing, and even fewer have taken the approach
of putting down chemically active biomolecules on
"We wanted to see if we could steal functionality
from biology to make the complex structures we need,"
says Chilkoti. The outcome, he says, was everything
he and his colleagues could have hoped for: "In
an afternoon, we inexpensively created a nanostructure
that would have taken weeks to develop using expensive,
traditional methods of etching circuits into chips."
Now that the team has demonstrated that enzymes can
"subtract" from the substrate to make precise
troughs, they envision many other possibilities. Instead
of using enzymes that degrade DNA, for example, they
could use other enzymes that link DNA strands together.
That would allow them to make "additions"
to the substrate, causing the DNA layer to grow thicker
in certain places. Alternatively, they could use still
other enzymes that make chemical changes in the DNA
substrate itself, allowing them to build complex structures
with "different colored bricks," as Chilkoti
The team could even do away with the DNA entirely,
and use a different substrate, Chilkoti says. "We
used DNA because it is pretty robust, because you
can buy synthetic DNA strands off the shelf, and because
there are lots of enzymes that work on it. But there
is nothing unique about it for this kind of application."
"Enzymes have evolved to carry out an incredible
variety of processes," comments team member Stephen
Craig, a Duke chemist. "By harnessing the diverse
power available in nature, it may be possible to selectively
erase structures at one point, add structures at a
second location, transform them from one state to
another at a third location, and so on. The potential
exists to create very small and very complex architectures."
"A lot more work is needed to optimize the process,
but we feel this enzyme-inking technique has tremendous
promise for wide applicability," says Chilkoti.
"Enzyme-based nanomanufacturing is of interest
because it could an incredibly versatile tool. This
is critical because nanomanufacturing is at the heart
of efforts to see if we can make new devices that
are far smaller, cheaper, faster and better than existing
devices," says Chilkoti.
To date, dip-pen nanolithography has been primarily
a bench top laboratory technique.
Scaling up the technique to truly make it a viable
manufacturing technique will require new instrumental
technology such as dip-pen lithography machines with
multiple, articulated tips that can move independently
to deposit several different types of enzymes. Chilkoti
envisions machines that can work on a sheet of chips
using different enzymes, so that the chips can be
snapped apart after the enzyme inking and processing.
Chilkoti notes that such machines are already being
commercially developed, so the day might not be too
far off when enzyme-based nanomanufacturing might
be possible on an industrial scale.
web site: http://bme-www.egr.duke.edu/personal/chilkoti/research.html
Investigator: Ashutosh Chilkoti, Duke University