“The assembled DNA structures are relatively large–a hundred to 150 nanometers on an edge–but they are composed of strips of DNA that are only about 2 nanometers tall,” said Wallraff. “Once we put these relatively large nanostructures down, then we can use them for component assembly of, for example, silicon nanowires, carbon nanotubes and quantum dots.”
“In principle, we can use 130-nanometer lithography to get down to feature sizes that are much, much smaller,” Wallraff claimed.
The DNA strands were customized by Rothemund to create a pattern of chemical hooks to which nanoscale components will self-assemble into a circuit. The sticky patches created by IBM on the substrate then attracted the preassembled circuits, which automatically attached themselves in the correct orientation.
By self-assembling the circuits atop the DNA strands in a solution, it could eventually be possible to merely bath the substrate in the solution, prompting circuits to automatically attach themselves.
“In a single drop of water, we assembled more than 100 billion copies of the desired shape with a pattern on top to which components could be attached,” said Rothemund. “The spacing between the components can be as small as 6 nanometers, giving you a resolution today that is about 10 times higher than the lithographic resolution we use today to make computer chips.”
So far, the team has demonstrated alignment of circuit assemblies onto the sticky patches with an orientation accuracy of less than 10 degrees. Remaining technical hurdles include attaching the components to the hooks on DNA, interconnecting components on DNA strands and connecting pre-assembled circuits.
“Alignment, registration and overlay is extremely critical, so we are currently trying to understand what the tolerances are–how well we can position these and realign them if they get a little off,” said Wallraff.
The remaining engineering hurdles will take at least five years to perfect into a process that could be commercialized, according to Rothemund
IBM’s Almaden Research Center and at the California Institute of Technology researchers are suggesting that artificial DNA nanostructures and ‘DNA origami’, in which a long single strand of DNA is folded into a shape using shorter “staple strands”, could be used to provide a template for the self-assembly of other materials into nanoelectronic or nano-optical devices on the surface of the chip. They say their approach of using DNA molecules as scaffolding — where millions of carbon nanotubes could be deposited and self-assembled into precise patterns by sticking to the DNA molecules – may provide a way to reach sub-22 nm lithography. The utility of their approach, they say lies in the fact that the positioned DNA nanostructures can serve as scaffolds, or miniature circuit boards, for the precise assembly of components – such as carbon nanotubes, nanowires and nanoparticles – at dimensions significantly smaller than possible with conventional semiconductor fabrication techniques. This opens up the possibility of creating functional devices that can be integrated into larger structures, as well as enabling studies of arrays of nanostructures with known coordinates. the DNA origami could allow chipmakers to build frameworks that are far smaller than possible with conventional tools, the technique still needs perhaps ten years of experimentation and testing. The researchers used electron-beam lithography and an etching process to create DNA origami-shaped “binding sites” on silicon and other materials used in making semiconductors. The techniques for preparing DNA origami, developed at Caltech, cause single DNA molecules to self assemble in solution via a reaction between a long single strand of viral DNA and a mixture of different short synthetic oligonucleotide strands. These short segments act as staples – effectively folding the viral DNA into the desired 2D shape through complementary base pair binding. The short staples can be modified to provide attachment sites for nanoscale components at resolutions (separation between sites) as small as 6 nanometers. In this way, DNA nanostructures such as squares, triangles and stars can be prepared with dimensions of 100 – 150 nm on an edge and a thickness of the width of the DNA double helix. The lithographic templates were fabricated at IBM using traditional semiconductor techniques to etch out patterns. Either electron beam or optical lithography were used to create arrays of binding sites of the proper size and shape to match those of individual origami structures. Key to the process were the discovery of the template material and deposition conditions to afford high selectivity so that origami binds only to the patterns of “sticky patches” and nowhere else.
Artificial DNA nanostructures show promise for the organization of functional materials to create nanoelectronic5 or nano-optical devices. DNA origami, in which a long single strand of DNA is folded into a shape using shorter ‘staple strands’, can display 6-nm-resolution patterns of binding sites, in principle allowing complex arrangements of carbon nanotubes, silicon nanowires, or quantum dots. However, DNA origami are synthesized in solution and uncontrolled deposition results in random arrangements; this makes it difficult to measure the properties of attached nanodevices or to integrate them with conventionally fabricated microcircuitry. Here we describe the use of electron-beam lithography and dry oxidative etching to create DNA origami-shaped binding sites on technologically useful materials, such as SiO2 and diamond-like carbon. In buffer with 100 mM MgCl2, DNA origami bind with high selectivity and good orientation: 70–95% of sites have individual origami aligned with an angular dispersion (1 s.d.) as low as 10° (on diamond-like carbon) or 20° (on SiO2).39 pages of supplemental information on the research
Brian Wang is a Futurist Thought Leader and a popular Science blogger with 1 million readers per month. His blog Nextbigfuture.com is ranked #1 Science News Blog. It covers many disruptive technology and trends including Space, Robotics, Artificial Intelligence, Medicine, Anti-aging Biotechnology, and Nanotechnology.
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