"By providing a simple and robust approach capable of patterning DNA with high precision over a large area, our technique may significantly promote the development of nanowire-based devices," Jingjiao Guan of Ohio State told nanotechweb.org. "Analysis on a single stretched DNA can give highly valuable genetic and medical information. By patterning a large quantity of stretched DNA molecules into a well-defined array, parallel and automated analysis may be realized to achieve higher throughput and reliability. As a result, novel DNA chips may be constructed."

To create the arrays, Guan and colleague James Lee pressed patterned stamps made from polydimethyl siloxane (PDMS) into a solution of DNA molecules on a glass coverslip. They applied pressure for 5 s before peeling up the stamp from one end, transferring DNA molecules to the stamp as they went. The molecules tended to orient themselves in the direction that the meniscus of the solution was receding. Finally, placing the stamp on a solid surface for one minute without external pressure transferred the DNA to the surface, in a process known as contact printing.

A typical stamp contained microwells 5 µm in diameter, 4 µm deep and situated with a centre-to-centre distance of 8 µm. The team found that peeling the stamp away from the DNA solution fast-formed short nanostrands, as the DNA tended to break at the edges of the microwells. Peeling the stamp away slowly, on the other hand, formed long strands of DNA, up to several hundred micrometres long, because consecutive nanostrands tended to bundle together.

By repeating the process with the stamp in a different orientation, the team was able to create discrete crosses of short DNA strands or a crossbar structure of long DNA strands.

"We are trying to build a working device, for example, a sensor, in which DNA nanostrands will be coated with functional materials to make nanowires able to sense environmental stimuli," said Guan. "We hope the well-defined nanowire array prepared by our technique will make the sensor more sensitive and reliable than its counterparts made by other methods."

The researchers reported their work in PNAS.