Good things really do come in small packages, according to a group of students at Harvard University. They constructed a tiny container--about 30 nanometers in diameter--made entirely of DNA, which could one day be used to deliver drugs or gene or protein-based therapies to specific tissues in the body.

"We know DNA is a very stable building material," says Valerie Hoi-Ting Lau, one of the students involved in the project. "Now we're trying to take advantage of the fact that it's programmable." Lau and others presented their barrel at the International Genetically Engineered Machines competition at MIT earlier this month (see "Bizarre Bacterial Creations").

The world of DNA architecture has exploded in recent years, with scientists building two-dimensional smiley faces and complex maps, as well as three-dimensional octagons. The chemicals that make up long, winding DNA molecules bind together according to a predictable set of rules, so it's possible to design DNA sequences that will form into various shapes.

While DNA architecture previously took years to design and construct, a method developed earlier this year provides a relatively easy way to program DNA into specific shapes (see "Do-It-Yourself Nanotech"). A single long strand of DNA is studded with shorter snippets of specially designed DNA sequences that act as the chemical equivalent of staples. Each snippet will only bind to a specific spot on the DNA molecule. Strategically placing these staples along the DNA strand allows the molecule to self-assemble into different shapes.

By adapting this method to build three-dimensional structures, the students and their advisor William Shih, a Harvard scientist who has been a leader in DNA architecture, designed a DNA sequence that would fold into a tiny, hollow container. The final structure, which is shaped like an open barrel, consists of a single DNA molecule that zigzags back and forth to create a pleated sheet. The sheet is programmed to curve around on itself, creating a double-walled cylinder. (Click here to see pictures of the barrel.)

"It was really a breakthrough result," says Shih. Previous DNA containers, such as octagons, have had large holes in their walls, but researchers think the walls of this structure are quite solid, theoretically allowing the barrel to safely encase nanosize treasures.