Monday, February 08, 2016

pluripotent matter: building complex nanostructures with DNA



sciencemag |  Researchers have engineered tiny gold particles that can assemble into a variety of crystalline structures simply by adding a bit of DNA to the solution that surrounds them. Down the road, such reprogrammable particles could be used to make materials that reshape themselves in response to light, or to create novel catalysts that reshape themselves as reactions proceed.

“This paper is very exciting,” says Sharon Glotzer, a chemical engineer at the University of Michigan, Ann Arbor, who calls it “a step towards pluripotent matter.” David Ginger, a chemist at the University of Washington, Seattle, agrees: “This is a proof of concept of something that has been a nanoparticle dream.” Neither Glotzer nor Ginger has ties to the current research.

The dream started decades ago when chemists first discovered ways to synthesize nanoparticles, clumps of atoms below 100 nanometers in size. Researchers quickly began looking for ways to control how these particles assembled in order to build new materials from the bottom up.

Today, few materials are built from scratch. One exception is laser materials, which are used in everything from telecommunications gear to barcode scanners. But the materials, formed by adding atoms on a surface layer by layer, are very expensive to make, and severely limited in size. Assembling nanoparticles could offer a new way to grow larger—and more varied—materials cheaply. But in most cases, mastering the level of control needed to do this has turned out to be elusive.

One approach that has worked well was pioneered by chemist Chad Mirkin and colleagues at Northwestern University, Evanston, in Illinois. Mirkin’s team decorated the outer surface of gold nanoparticles with snippets of single-stranded DNA, and then used those strands like Velcro to link together neighboring particles. As the separate particles approached one another, the strands knitted themselves into the more common form of double-stranded DNA, holding the particles together. Over the years, Mirkin’s team showed that it could use this setup as a means to coax particles coated with different sequences to assemble into different types of crystals, creating powerful sensors for detecting specific DNA strands and proteins in the process. But despite the success of this approach, each time the team wanted to build a material with a new crystal orientation, it had to re-engineer its DNA linkers.