MUNICH, Germany, April 11 (UPI) -- German researchers said on Thursday they have turned to lasers to produce visible-light images of items a few percent the size of the light waves themselves, something previously considered unachievable.
Reporting in the journal Physics Review Letters, Professor Stefan Hell and his High Resolution Microscopy team at the Max Planck Institute for Biophysical Chemistry describe how an interference pattern of opposing laser beams allows them to view objects about 5 percent the size of the light waves themselves.
This overcomes what previously had been thought of as a basic limitation of optical microscopes -- since light waves diffract through lenses, the scope could not focus on details smaller than about a third of the wavelength of light being used.
"Our technique works only for fluorescent (emitted) light, not reflected light," Hell told United Press International from Munich. "But fluorescent light covers about 80 percent of the applications dealing with biology."
The team's method involves two colors of lasers, green and red. The green laser excites a dye in the object being observed, which then gives off light. The red laser stops the dye from emitting light but the beam is split so it approaches the object from opposite directions.
By adjusting the beams precisely, an intereference "valley" about 30 to 50 nanometers wide is formed where no red light enters, letting the fluorescent light come from a much sharper focus. A nanometer is to an inch what an inch is to 400 miles.
The Max Planck team has proven the concept on the laboratory bench, Hell said, and moving forward is a matter of determining which dyes will work best with particular biological processes and light wavelengths. The team has produced optical images of bacterial membranes only 30 nanometers thick -- earlier optical images would show blobs about 800 nanometers wide.
"Theoretically, by further increasing the intensity of the laser we could obtain resolution of individual molecules," Hell said. "The drawback is that the energy levels necessary to do so would likely destroy the object."
That is exactly the problem with using non-optical methods, such as electron microscopes, to observe nanoscale activity in organic materials, said Mike Roco, chief nanotechnology adviser at the U.S. National Science Foundation. There are experiments with focused beams of ions, or electrically charged atoms, that can match the results of the new optical method and create 3-D images, but they can only be performed on inorganic materials, Roco told UPI Thursday.
"It's interesting how we pass what was thought to be an absolute limit in only a few years," Roco said. "Everybody 'knew' you couldn't (optically) see an object under 100 nanometers. This is a very clever idea ... with tremendous potential impact."
The scale visible in the new technique could allow researchers to observe the basic structure of tissue such as bone or watch biological motors work in real time and in fine detail, Roco said.
Such motors, only about 11 nanometers tall and 11 nanometers in diameter, produce enough energy to do work equivalent to a human spinning a telephone pole about 1 mile long at eight revolutions per second in a swimming pool, researchers have said.
The biotech industry also could benefit from the work, said Mark Modzelewski, executive director of the NanoBusiness Alliance, a New York City-based organization fostering the acceptance of nanotech. Researchers currently use a lot of guesswork to determine how drugs are delivered to cells, but the Max Plank team's technique could allow them to watch such interactions in real time, Modzelewski told UPI.
