Molecule does two-step

Duke University researchers have found a way to make a molecule react only when it has been hit by two photons of ultraviolet light, making the molecule a controllable switch.

The molecule could eventually be used in optical storage devices and in biochips.

The stronger a beam of light, the more likely a single molecule will be hit by a pair of photons rather than just one. This makes it possible to use an intense beam or intersecting beams to selectively switch molecules.

The researchers' scheme improves on previous work because the two photons don't have to hit the molecule simultaneously. The effect of a single photon hit is also reversible; partially activated molecules can be reset.

The scheme could be used in DNA chips containing thousands of DNA molecules designed to carry out different tests. Because the method trips a reaction only where light is focused, test strands of DNA could be packed closely. The researchers are working on attaching the molecules to individual DNA bases.

The molecule's on and off states could also represent the 1s and 0s of computer information in molecular memory chips, or act as light-controlled switches in schemes to release drugs at specific locations in the body.

The method could be used to make DNA arrays within a year, according to the researchers. The work appeared in the October 6, 2003 issue of the Proceedings of the National Academy Of Sciences.