Thursday, January 31, 2008

Programming Advanced Materials

Continued from page 1

By Peter Fairley

The result is exactly what theory predicts: a crystal lattice in which each particle of one type is surrounded by eight of the others marking the corners of a cube. Mirkin's group further demonstrated that tweaking the temperature and DNA sequences could nudge the same mix of particles to form a distinct crystal structure in which each particle has 12 neighbors.

Mirkin says that he and his team are just getting started. "To me, it's really only the start rather than the ending," he says. Over the past three years, Mirkin's group has been demonstrating methods to place different DNA linkers on different faces of nonspherical particles, such as triangle-faced prisms and virus particles. That, he says, should enable programming of more complex materials with repeating patterns of three or more components. "The really intriguing possibility here is the ability to program the formation of any structure you want," says Mirkin.

Stroud says that the structures already produced will be useful as the DNA-programmed assembly is extended to particles other than gold. Applications could include photonic crystals, in which the precise periodicity of particles can tune the overall materials to manipulate specific wavelengths of light, and photovoltaics that capture a broader range of the solar spectrum.

The structures are highly porous--10 percent particles and DNA and 90 percent water. That could hinder applications in which water is undesirable. Drain out the water, and the crystals collapse. Gang says that one could stabilize the crystals by filling the lattice with a polymer, but he is also exploring alternate stabilization schemes that would preserve the lattice's open space.