Although nanoscale building blocks can self-assemble into ordered structures, it is difficult to precisely position these blocks in 3D. Such control will be needed to produce technologically useful materials in the future.

Now, Chad Mirkin and George Schatz at Northwestern University and colleagues have used the interactions between complementary DNA molecules attached to gold particles to make the particles assemble into crystals with a well-defined symmetry. Meanwhile, Oleg Gang of Brookhaven National Laboratory and co-workers have interacted complementary DNA strands with nanoparticles to make crystals whose structure can be tuned by heating.

Rapid self assembly
Both the Mirkin-Schatz and Gang teams attached DNA to gold particles, measuring around 10 nm across, to make two sets of DNA-topped gold nanoparticles. Each particle has several tens of DNA strands attached to it and the ends of the strands on one set of particles adhere to the strands of the other set. By mixing the two sets together, the scientists observed that the nanoparticles rapidly self-assembled into well-ordered arrays with a body-centred-cubic structure as the strands "hybridized" to form a double helix.

The scientists also observed that there are DNA "spacers" connecting the binding regions on the nanoparticles. "Although there are many bifunctional materials one could consider for interconnects, DNA is the most programmable and reliable," said Mirkin. "In addition, it allows one to control the spacing of the nanoparticles over much larger distances than small molecule interconnects."

Other complex structures
Mirkin's team now plans to selectively functionalize the different faces and edges of a nanoparticle with various DNA strands to create the equivalent of linear, trigonal, pyramidal and perhaps even octahedral crystals. "This will open up the possibility of making almost any type of crystal structure from inorganic materials and DNA interconnects," he explained.

Gang's group is also planning to create other complex structures using DNA-encoded nanoparticle interactions and exploring the unique optical and mechanical properties of these materials. "Using biomolecules to control the formation of ordered nanosystems will allow us to build 'artificial atoms' from nanoparticles and assemble them into new classes of materials," said Gang.

Both teams published their work in Nature.