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Brown Engineers Use DNA to Direct
Nanowire Assembly and Growth
A research team led by Brown University engineers has
harnessed the coding power of DNA to create zinc oxide
nanowires on top of carbon nanotube tips. The feat,
detailed in the journal Nanotechnology, marks the first
time that DNA has been used to direct the assembly and
growth of complex nanowires.
The tiny new structures can create and detect light
and, with mechanical pressure, generate electricity.
The wires' optical and electrical properties would allow
for a range of applications, from medical diagnostics
and security sensors to fiber optical networks and computer
circuits.
"The use of DNA to assemble nanomaterials is one
of the first steps toward using biological molecules
as a manufacturing tool," said Adam Lazareck, a
graduate student in Brown's Division of Engineering.
"If you want to make something, turn to Mother
Nature. From skin to sea shells, remarkable structures
are engineered using DNA."
Lazareck, who works in the laboratory Jimmy Xu, professor
of engineering and physics, led the research. The work
is an example of "bottom up" nanoengineering.
Instead of molding or etching materials into smaller
components, such as computer circuits, engineers are
experimenting with ways to get biological molecules
to do their own assembly work. Under the right chemical
conditions, molecular design and machinery – such
as light-sensing proteins or viral motors – can
be used to create miniscule devices and materials.
Engineers in the lab of Jimmy Xu used
DNA to grow zinc oxide nanowires like this one on the
tips of carbon nanotubes. The zinc oxide wires created
in the lab measured between 100 and 200 nanometers long.
(Image: The Xu Laboratory)
In this work, the team of engineers and scientists
took the "bottom-up" approach one step further
by successfully harnessing DNA to provide instructions
for this self-assembly. The new structures created in
the Xu lab are the first example of DNA-directed self-assembly
and synthesis in nanomaterials.
The Xu lab is the first in the world to make uniform
arrays of carbon nanotubes. Lazareck and his collaborators
at Brown and Boston College built on this platform to
make their structures. They started with arrays of billions
of carbon nanotubes of the same diameter and height
evenly spaced on a base of aluminum oxide film. On the
tips of the tubes, they introduced a tiny DNA snippet.
This synthetic snippet of DNA carries a sequence of
15 "letters" of genetic code. It was chosen
because it attracts only one complement – another
sequence made up of a different string of 15 "letters"
of genetic code. This second sequence was coupled with
a gold nanoparticle, which acted as a chemical delivery
system of sorts, bringing the complementary sequences
of DNA together. To make the wires, the team put the
arrays in a furnace set at 600° C and added zinc
arsenide. What grew: Zinc oxide wires measuring about
100-200 nanometers in length.
The team conducted control experiments – introducing
gold nanoparticles into the array with no DNA attached
or using nanotubes with no DNA at the tips in the nanotube
array – and found that very few DNA sequences
stuck. And no wires could be made. Lazareck said the
key is DNA hybridization, the process of bringing single,
complimentary strands of DNA together to reform the
double helices that DNA is famous for.
"DNA provides an unparalleled instruction manual
because it is so specific," Lazareck said. "Strands
of DNA only join together with their complements. So
with this biological specificity, you get manufacturing
precision. The functional materials that result have
attractive properties that can be applied in many ways."
"We're seeing the beginning of the next generation
of nanomaterials," said Xu, senior author of the
article. "Many labs are experimenting with self-assembly.
And they are making beautiful, but simple, structures.
What's been missing is a way to convey information –
the instruction code – to make complex materials."
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