Ames Laboratory, U.S. Department of Energy, Ames, Iowa Ames Laboratory, U.S. Department of Energy, Ames, Iowa
Ames, Iowa -- Scientists at the U.S. Department of Energy's Ames Laboratory have developed a technique to "zero in on" and monitor the meanderings of single molecules in solution to gain insight on each step of a chemical reaction, which could ultimately lead to improved treatments for AIDS and cancer.
"The ability to observe one molecule react with another molecule may have great implications in the fields of catalysis, medicine and biotechnology," says Ed Yeung, Ames Lab program director for Physical and Biological Chemistry and distinguished professor of chemistry at Iowa State University (ISU). "Looking ahead, maybe we'll be able to detect a single HIV virus or one copy of a specific gene in DNA."
Working with Xiao-Hong Xu, a postdoctoral fellow at the Lab, Yeung is now able to track the motion of single molecules of rhodamine, a highly fluorescent compound, and rhodamine-labeled DNA in water solution. Their research was published in the Feb. 21 issue of Science.
Other techniques can detect single molecules in solution, but Yeung says his and Xu's is the first to offer continuous monitoring. The ability to follow single molecules makes it possible to collect detailed information about their individual behaviors and physical and chemical properties. This represents a significant advancement over traditional methods, which determine the characteristics of molecules based on population averages.
Yeung describes the new technique as a relatively simple combination of an optical microscope and an intensified charge-coupled device (ICCD) camera. Carefully adjusted laser power is used to induce a molecule in solution to emit light. The light is collected by the optics of the microscope and imaged on the camera, which records the dynamics of the molecule of interest, gathering data with submillisecond time resolution.
"A CCD camera is just a sophisticated camcorder," says Yeung, "but there's a special way of operating it that gives you time resolution that's maybe a hundred times, or even more, faster than prior techniques, which can't look at molecules in solution at that kind of speed."
Speed in data collection is essential since molecules in solution cannot be kept in a confined space. To help achieve the necessary speed, Yeung uses high-sensitivity and high-speed electronics to image either a thin layer of solution or a liquid-surface interface. This makes it possible to follow the same single molecule continuously, obtaining molecular motion and other kinetic information.
"Now we can actually follow the behavior of molecules," says Yeung. "In the gas phase, people have been able to monitor single molecules for a long time, because in gases you have better control and fewer interfering species. Now we're bringing that kind of study to the solution phase, where most chemical and biochemical reactions occur."
Ames Laboratory is operated for the DOE by ISU. The Lab conducts research into various areas of national concern, including energy resources, high-performance computing, environmental cleanup and restoration, and synthesis and study of new materials.
Contact: Saren Johnston
ph: 515-294-3474
Ed Yeung
ph: 515-294-8062
Last revision: 4/17/98 sd
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