30 nanometer diameter DNA Barrels

A group of students at Harvard University have constructed 30 nanometers in diameter DNA containers. The DNA barrels could one day be used to deliver drugs or gene or protein-based therapies to specific tissues in the body.

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. 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.

Some DNA-based structures have an inherent floppiness that makes three-dimensional shapes collapse. But the building method used to create the barrel–lining up a series of DNA helices into a pleated-sheet structure–seems to provide new strength.

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