Lasers snatch free-floating DNA

By Kimberly Patch, Technology Research News

Working with individual DNA molecules is tricky.

Current technologies involve chemically binding each DNA molecule to a plastic bead, then trapping and moving the bead by hitting it with an intense beam of photons from a laser. A team of researchers from Japan has found a way to drag DNA molecules around without attaching them to a larger object.

The researchers' first approach was to sandwich the DNA between unconnected beads and move the DNA indirectly by bombarding the beads with a laser, said Akira Mizuno, a professor of electrical engineering at the Toyohashi University of Technology and a professor of electronic engineering at the University of Tokyo in Japan.

Although that method worked, it required a high degree of skill to carry out. The researchers went on to find an easier way: they made the beads much smaller and used many more of them. "We used many fine particles... to support a DNA molecule," he said.

Key to the method is the size of the beads. The researchers found that a laser beam would trap, or aggregate a cluster of more than 40 beads that were 200 nanometers in diameter, but would only trap a few beads half that size.

To demonstrate the technique, the researchers put the DNA in a solution that contained 200-nanometer beads. When they focused a laser beam into the solution, a group of beads aggregated at the point of focus. When they focused the beam at the end of a single DNA molecule, a group of beads packed tightly together around that point, and the researchers used the bead cluster to drag the end of the molecule.

The molecule can be released and retrapped by switching the laser off and on, and a single DNA molecule can be manipulated at any point along its length, according to Mizuno. The technique allows researchers to transport, stretch, or keep a DNA molecule in place, he said.

Combined with florescent labeling, which tags a molecule so that it can be seen through an optical florescent microscope, the method allows for real-time handling of DNA molecules, said Mizuno.

"This... can be applied to investigate interactions between a DNA and other protein molecules because we can fix a molecule precisely," which allows for higher-resolution imaging, Mizuno said.

DNA molecules are made up of paired strings of bases held together by phosphate backbones. The order of the four types of bases is a sort of code that allows a cell to make many different proteins. An individual gene is a segment of a DNA molecule that serves as a template to make a specific protein.

The microparticle method is interesting and useful, said Kenichi Yoshikawa, a physics professor at the University of Kyoto in Japan. The microparticle method opens up new possibilities because it makes it possible to manipulate an individual DNA molecule without binding it to a bead, he said.

The method also gives researchers the ability to analyze giant DNA molecules, he said. Present technology can treat a DNA molecule only below the size of 100,000 base pairs, he said. The 46 DNA molecules that make up the 23 human chromosomes are much larger than this -- around 10 million base pairs each. "Presently experimentalists are obliged to cut the large DNA molecules to small fragments," to analyze them, he said.

The researchers are working on using the process to develop ways to analyze DNA more rapidly, said Mizuno.

Mizuno's research colleagues were Ken-ichi Hirano and Yoshinobu Baba from the University of Tokushima, and Yukiko Matsuzawa from the Toyohashi University of Technology. They published the research in the January 21, 2002 issue of Applied Physics Letters. The research was funded by the Japanese Ministry of Education, Science and Technology's Japan Science and Technology Corporation and the Japanese Ministry of Economy, Trade and Industry's Joint Center for Atom Technology.

Timeline:   < 2 years
Funding:   Government
TRN Categories:   Biology; Biotechnology; Nanotechnology
Story Type:   News
Related Elements:  Technical paper, "Manipulation of Single Coiled DNA Molecules by Laser Clustering of Microparticles," Applied Physics Letters, January 21, 2002.


March 20/27, 2002

Page One

Monkey think, cursor do

DNA solves big problem

Carving beams shrink circuits

Lasers snatch free-floating DNA

Etching could boost disk capacity


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