Detector senses single DNA

Double-stranded DNA forms the famous double-helix shape. Keep a single strand of DNA separated from its other half, however, and it coils like a loose ball of yarn. The single strand can also stretch more than the double helix.

Researchers from the University of California at Los Angeles have tapped these differences in shape to make a sensor capable of detecting a single DNA molecule.

The device could eventually identify genetic markers for diseases including cancer and changes in DNA left by diseases like leukemia, according to the researchers. It could also be used to monitor small pools of cells like those used in stem cell research and in testing the response of cells to new drugs, according to the researchers.

The sensor consists of a micron-sized bead connected to a flat surface by a single strand of DNA. The bead is repulsed by the surface and so pulls the strand straight. When the DNA comes in contact with a DNA strand it can combine with, the interaction shortens the tether by a few nanometers. A micron is one thousandth of a millimeter; a nanometer is one thousandth of a micron, or the span of ten hydrogen atoms. The device identifies this change by sensing differences in the way the bead scatters light.

The method could be used to make hand-held DNA detectors in two to three years, according to the researchers. The work appeared in the June 24, 2003 issue of the Proceedings of the National Academy of Sciences.