DNA links gold into new materials.

Much as a sculptor might add bits of clay together to form a statue, scientists are trying to build materials from nanometer-size particles.

Constructing a material from the most basic components gives the scientist ultimate control over all of its properties.

Now, two research teams have found a way to build a material out of tiny gold beads by using DNA to link them. The result is a composite of inorganic particles and organic molecules that has potential applications in biological sensing and electronics.

Both groups' methods take advantage of DNA's base-pairing properties. Chad A.

Mirkin, Robert L. Letsinger, and their colleagues at Northwestern University in Evanston, Ill., attached DNA strands of two different sequences to gold particles 13 nanometers in diameter suspended in water. The DNA stuck out in all directions, making the particles look like furballs.

Then they added to the solution strands of DNA whose ends had sequences that complemented the strands on the gold particles. Like Velcro, the DNA hooked the individual furballs together, forming larger aggregates. This process changed the color of the solution.

Peter G. Schultz, A. Paul Alivisatos, and their colleagues at the University of California, Berkeley took a slightly different approach. They attached a single DNA strand to each gold particle. Allowing those modified particles to connect to a long DNA template produced microscopic daisy chains of two or three gold particles each. Both reports appear in the Aug. 15 Nature.

One powerful application of this research may be in detection of microbes or identification of organisms. "You could design a series of [particles] that can latch onto a biological sequence," Mirkin says. By changing color, probes based on this technique would signal the presence of a specific DNA or RNA sequence.

The unusual composite material may have desirable electronic properties as well. Jacqueline Barton, a chemist at the California Institute of Technology in Pasadena, demonstrated several years ago that electricity can flow through single strands of DNA. The new work, she says, "establishes a scheme for constructing large arrays [of metal particles]."