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Research: DNA enables precise graphene patterns

Posted: 15 Apr 2013 ?? ?Print Version ?Bookmark and Share

Keywords:MIT? Harvard University? DNA? graphene? nanostructure?

A team of chemical and molecular engineers at MIT and Harvard University have found a way to use DNA aimed at nanoscale applications. By using folded DNA to control the nanostructure of inorganic materials, they used the molecules as templates to create nanoscale patterns on sheets of graphene.

"This gives us a chemical tool to program shapes and patterns at the nanometre scale, forming electronic circuits, for example," noted Michael Strano, a professor of chemical engineering at MIT and a senior author of a paper.

Peng Yin, an assistant professor of systems biology at Harvard Medical School and a member of Harvard's Wyss Institute for Biologically Inspired Engineering, is also a senior author of the paper, and MIT postdoc Zhong Jin is the lead author. Other authors are Harvard postdocs Wei Sun and Yonggang Ke, MIT graduate students Chih-Jen Shih and Geraldine Paulus, and MIT postdocs Qing Hua Wang and Bin Mu.

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 neighbours.

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Metallized DNA (red) forms letters on a graphene surface. Treatment with oxygen plasma etches the shape of the letters into the graphene.

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 stated.

Instead, he and his colleagues transferred the precise structural information encoded in DNA to sturdier graphene. The chemical process involved is fairly straightforward, Strano said: 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 research team used this technique to create several types of shapes, including X and Y junctions, as well as rings and ribbons. They found that although most of the structural information is preserved, some information is lost when the DNA is coated in metal, so the technique is not yet as precise as another technique called e-beam lithography.

However, e-beam lithography, which uses beams of electrons to carve shapes into graphene, is 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.

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