Singling out molecules in solution.

A newly developed technique for detecting individual dye molecules in solution may lead to a high-speed method for determining the base sequences that make up a single strand of DNA. The observation technique, developed by E. Brooks Shera and his co-workers at the Los Alamos (N.M.) National Laboratory, involves passing an extremely dilute solution containing dye molecules down a plastic tube and through a tightly focused laser beam. The pulsed laser light excites the dye molecules one at a time, causing them to emit light, or fluoresce. Thus, each passing molecule generates a readily detectable flash of light.

This work represents the first efficient detection of individual fluorescent molecules in solution, Shera says. Such a technique should have a variety of applications in biological and chemical science.

Applying the method to DNA sequencing requires tagging each type of base along a DNA strand with a chemical marker that fluoresces at a particular wavelength. By using enzymes to snip off one base at a time from the strand, then letting each cleaved, tagged base travel past a laser beam and detector, scientists could identify each base in the proper order. However, the Los Alamos researchers have yet to work out the details of how to tag DNA and other molecules of interest.