Harvard biologists have brought new meaning to the term "fine print" by devising microscopic tiles made of DNA that self-assemble into letters, Chinese characters, emoticons and other shapes.

More than mere doodling, their advance, detailed this week in the journal Nature, could make it easier and cheaper to build tiny DNA devices capable of delivering drugs or aiding the study of biochemistry, scientists said.

"This technique will accelerate the research field of DNA nanotechnology," said Ebbe Sloth Andersen, a researcher at Aarhus University in Denmark who collaborated on an editorial that accompanied the report.

In its usual role as a warehouse for storing genetic information, DNA helps build humans and hummingbirds, maple trees and meerkats all sorts of complex organisms. But as a building material for machines smaller than the smallest bacterium, it has been tough to control.

Since the early 1980s, engineers have experimented with a variety of approaches to create structures out of DNA, including the use of tiles small bricks woven together out of several strands of DNA that could stick to one another and self-assemble into shapes.

But when researchers tried to construct precisely defined shapes, they ran into trouble, said Peng Yin, a systems biologist at Harvard's Wyss Institute in Boston and senior author of the Nature study. The tiles tended to stick together incorrectly, resulting in incomplete structures.

"People thought this couldn't work," Yin said.

But he and his collaborators pressed on, ultimately designing bricks out of single rather than multiple strands of DNA.

The strands each had four sequences of 10 or 11 bases, which could bind to complementary sequences of 10 or 11 bases on other tiles. If all four sequences on the edges of a tile bind with their matching counterparts on neighboring tiles, the tile assumes a rectangular shape.

The scientists programmed the tiles to stack up in a staggered formation, like a miniature brick wall. Then they created shapes by leaving out tiles at certain locations of their 64-by-103-nanometer "molecular canvas."

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Biologists construct self-assembling tiles of DNA