Tiles of DNA assemble with a designer fit.

A handy homeowner might take pride in designing a pattern of tiles to beautify a kitchen floor. Now, chemists at New York University have assembled some tiles of their own. Neither linoleum nor ceramic, these miniature plates are made of DNA.

Nadrian C. Seeman and his colleagues have designed rectangular, DNA blocks that readily assemble themselves into predictable, two-dimensional patterns. The team reports its findings in the Aug. 6 Nature.

Extended into three dimensions, these DNA arrays could act as scaffolding for building more complex materials with intricate, nanoscale structures, Seeman says. One of the group's collaborators, Erik Winfree of the California Institute of Technology in Pasadena is exploring the use of such crystals in DNA-based computers (SN: 7/13/96, p. 26).

By connecting two short, parallel strands of double-helix DNA at two places, the researchers created rigid tiles about 4 nanometers across and 13 or 16 nm long. They constructed the tiles to have different sticky ends--short stretches of unpaired bases that can match up with complementary bases on other tiles--enabling tiles to fit together in a precise way.

By assembling these tiles into a flat layout, the team created two distinct patterns of stripes, differently spaced. One arrangement used two types of tile and the other used four types

"We can generate predictable patterns on the [intermediate] scale by making specific alterations of sticky ends on the molecular scale," Seeman says. The tiles, mixed in a solution, come together to form crystals. Removed from the solution, dried, and examined with an atomic force microscope, the crystals look like striped sheets.

In order to view the pattern, the researchers attached a short loop of DNA to one type of tile in each set. The microscope, which works "basically like a phonograph needle," then detects the loop as a bulge on the face of the tile, Seeman explains. The images show stripes whose spacing corresponds to that expected for the tile size and pattern.

In an analogous way, researchers could attach other molecules to the tiles, perhaps a different molecule to each type differentiated by its particular sticky ends. Seeman and his colleagues are now working to create three-dimensional DNA crystals that could assemble materials having precisely controlled microstructures.