According to MIT News Office the scientists have found
the way how to exploit DNA for other purposes. By controlling DNA sequences,
they can manipulate the molecule to form many different nanoscale shapes.
Chemical and molecular engineers at MIT and Harvard
University have now expanded this approach using folded DNA to control the
nanostructure of inorganic materials. Firstly they have built DNA
nanostructures of various shapes, and then they used molecules as templates to
create nanoscale patterns on sheet of graphene. In general this could be a
giant step towards producing electronic chips made of graphene or
one-atom-thick layer with unique electronic properties.
Most of these DNA nanostructures are made using a
novel approach developed in Yin’s lab. Complex DNA nanostructures with
precisely prescribed shapes are constructed using short synthetic DNA strands
called single-stranded tiles. Each of these tiles acts like an interlocking toy
brick and binds with four designated neighbors.
Using these single-stranded tiles, Yin’s lab has
created more than 100 distinct nanoscale shapes, including the full alphabet of
capital English letters and many emoticons. These structures are designed using
computer software and can be assembled in a simple reaction. Alternatively,
such structures can be constructed using an approach called DNA origami, in
which many short strands of DNA fold a long strand into a desired shape.However,
DNA tends to degrade when exposed to sunlight or oxygen, and can react with
other molecules, so it is not ideal as a long-term building material. “We’d
like to exploit the properties of more stable nanomaterials for structural
applications or electronics,” Strano says.Instead, he and his colleagues
transferred the precise structural information encoded in DNA to sturdier
graphene. The chemical process involved is fairly straightforward, Strano says:
First, the DNA is anchored onto a graphene surface using a molecule called
aminopyrine, which is similar in structure to graphene. The DNA is then coated
with small clusters of silver along the surface, which allows a subsequent
layer of gold to be deposited on top of the silver.Once the molecule is coated
in gold, the stable metallized DNA can be used as a mask for a process called
plasma lithography. Oxygen plasma, a very reactive “gas flow” of ionized
molecules, is used to wear away any unprotected graphene, leaving behind a
graphene structure identical to the original DNA shape. The metallized DNA is
then washed away with sodium cyanide.
The team used unique technique to create several types
of shapes, including X and Y junctions, as well as rings and ribbons. With this
research they have found that some information is lost when the DNA is coated
in metal, so the technique is not yet as precies an another technique called
e-beam lithography. However the method of e-beam lithography uses beams of
electrons to carve shapes into graphene, is generaly expensive and takes a long
time, so it would be very difficult to scale it up to mass-produce electrical
or other components made of graphene. One shape of particular interest to
scientists is a graphene ribbon, which is a very narrow strip of graphene that
confines the material’s electrons, giving it new properties. Graphene doesn’t
normally have a bandgap — a property necessary for any material to act as a
typical transistor. However, graphene ribbons do have a bandgap, so they could
be used as components of electronic circuits.
In the longer term, the DNA nanostructure fabrication
strategy could help researchers design and build electronic circuits made of
graphene. This has been difficult so far because it’s challenging to place tiny
carbon structures, such as nanotubes and nanowires, onto a graphene sheet.
However, using the metallized DNA masks to arrange structures on a sheet of
graphene could make the process much easier.
The new approach is “conceptually novel,” says Robert
Haddon, a professor of chemical and environmental engineering at the University
of California at Riverside, who was not part of the research team. “The work
shows the potential of self-assembled metallized DNA nanoarchitectures as
lithographic masks for wafer-scale patterning of graphene-based electronic
circuit elements. I believe that this approach will stimulate further research
on the application of nanopatterning techniques in graphene-based nanoelectronics.”
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