Harvard University researchers have built a barrel-like structure, 30 nanometers in diameter, out of a long strand of DNA. The researchers studded the strand with short, specially designed snippets of DNA that can bind back to the strand, but only at specific spots. Strategic placement of the snippets caused the mole­cule to fold into different shapes. In the graphic at left (top left square), each circle represents a bird's-eye view of a standing double helix. After the snippets are placed, the molecule folds to create a sheet, which then curves around on itself, creating a double-walled barrel (other images). E. William Shih, a Harvard biologist and a leader in DNA architecture, who supervised the work, says such a device could someday be used to deliver drugs to specific tissues, but he concedes that "there's still quite a bit of work to be done."