“We have made what we believe is the most efficient self-assembly system so far demonstrated for the construction of the smallest scale features (<10>nanotechweb.org. “We have successfully patterned nucleic acids, proteins, ‘bulk’ metals and nanoparticulate metal, and we are near to achieving patterning with carbon nanotubes.”

LaBean and colleagues used tiles consisting of nine strands of DNA arranged into a cross shape. Each of the four arms of the cross terminated with four strands of DNA, while one strand of DNA participated in all four arms of the cross. At the centre of the tile was a square hole with T4 loops at each of its corners. The DNA tiles self-assembled into either nanoribbons or two-dimensional nanogrids, depending on the arrangement of their "sticky ends".

One configuration of the sticky ends resulted in the DNA tiles assembling into nanoribbons about 60 nm wide with an average length of 5 µm. In this assembly, the same face of each tile pointed in the same direction. But by reprogramming the arrangement of the DNA, the researchers caused the DNA tiles to self-assemble so that the same face was oriented up and down alternately in neighbouring tiles. This gave a nanogrid up to several hundred nanometres across with a distance of about 19 nm between the centre of each tile.

“The 4 x 4 tile was designed to make use of helix stacking and sticky-end connections in four directions in the lattice plane, in an attempt to regularize the growth of the tile lattice and produce objects with square aspect ratios,” said LaBean. “If the grid squares are thought of as pixels in an array, then one of our goals was to produce uniform pixel arrays with equal spacing between pixels in horizontal and vertical directions.”

LaBean and colleagues attached functional groups to the nanostructures by modifying the loops at the centre of each tile. For example, they incorporated a biotin group into some of the T4 loops so that they would link to the protein streptavidin. The researchers also metallized DNA nanoribbons with nanoparticles of silver. The resulting nanowires were roughly 35 nm high, 43 nm wide and up to about 5 µm long. By patterning metal leads to the nanowires, the scientists measured their resistance: they found that the wires had higher conductivity than other double-helix DNA-templated silver nanowires.

“Self-assembling DNA nanostructures may lead to advances in nano- and molecular electronics for computers, consumer goods, implantable medical devices, solar collectors, batteries and flat displays,” said LaBean. “DNA nanostructures lend themselves well to autonomous molecular devices, perhaps gene therapy agents, sensorless sorting of nanometre-scale objects, molecular medicines, diagnostics, and the assembly of nanopatterned materials for various chemistry and physics applications.”

Now, the scientists are working to increase the size of the assembled objects while decreasing the error rates, as well as increasing the complexity of the patterns they can form and attempting to generate addressable nano-arrays. “We are developing improved attachment chemistries and striving towards the fabrication and controlled deposition of functional electronic components, devices, circuits and systems,” added LaBean.

The researchers reported their work in Science.