dnacounter
Image: Courtesy CRAIGHEAD GROUP Cornell University

When it comes to analyzing biomolecules such as proteins or DNA, the tried-and-true test tube can only take you so far. It is for this reason that many scientists are working to create so-called labs-on-chips and other nanoscale devices, specially engineered to sort, measure and count the various molecules of life. Such inventions might make possible, among other things, far more accurate genetic and diagnostic tests. Harold Craighead, director of the Cornell Nanobiotechnology Center, described some of his own prototypes yesterday at the annual meeting of the American Association for the Advancement of Science (AAAS) in San Francisco.

The Craighead laboratory has worked on silicon-based alternatives to the organic gels used in DNA electrophoresis. The traditional technique relies on an electric field to pull fragments of DNA through the gel's tiny pores. Fragments of different lengths move at different speeds and ultimately collect in separate bands that can be photographed using fluorescent or radioactive tags. In Craighead's devices, silicon structures with tiny poresor forests of either columns or flat vanesreplace the gel. These nano-sieves need not sort only DNA molecules but could also separate proteins, carbohydrates or lipids. "This will expand the methods for analyzing very small amounts of biochemicals," Craighead says, "and create new abilities unanticipated by the test-tube methods.