[Editors] MIT develops 'tractor beam' for cells, more

[Elizabeth Thomson]

MIT News Office
Massachusetts Institute of Technology
Room 11-400
77 Massachusetts Avenue
Cambridge, MA  02139-4307
Phone: 617-253-2700
http://web.mit.edu/newsoffice/www

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MIT develops 'tractor beam' for cells, more

--Tool could manipulate tiny objects on a chip

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For Immediate Release
TUESDAY, OCT. 30, 2007
Contact: Elizabeth A. Thomson, MIT News Office -- Phone: 617-258-5402  
-- Email: thomson at mit.edu

PHOTOS AVAILABLE

CAMBRIDGE, Mass. - In a feat that seems like something out of a  
microscopic version of Star Trek, MIT researchers have found a way to  
use a “tractor beam” of light to pick up, hold, and move around  
individual cells and other objects on the surface of a microchip.

The new technology could become an important tool for both biological  
research and materials research, say Matthew J. Lang and David C.  
Appleyard, whose work is being published in an upcoming issue of the  
journal Lab on a Chip. Lang is an assistant professor in the  
Department of Biological Engineering and the Department of Mechanical  
Engineering. Appleyard is a graduate student in Biological Engineering.
	
The idea of using light beams as tweezers to manipulate cells and  
tiny objects has been around for at least 30 years. But the MIT  
researchers have found a way to combine this powerful tool for  
moving, controlling and measuring objects with the highly versatile  
world of microchip design and manufacturing.
	
Optical tweezers, as the technology is known, represent “one of the  
world's smallest microtools,” says Lang. “Now, we're applying it to  
building [things] on a chip.”
	
Says Appleyard, “We've shown that you could merge everything people  
are doing with optical trapping with all the exciting things you can  
do on a silicon wafer…There could be lots of uses at the biology-and- 
electronics interface.”
	
For example, he said, many people are studying how neurons  
communicate by depositing them on microchips where electrical  
circuits etched into the chips monitor their electrical behavior.   
“They randomly put cells down on a surface, and hope one lands on [or  
near] a [sensor] so its activity can be measured. With [our  
technology], you can put the cell right down next to the sensors.”  
Not only can motions be precisely controlled with the device, but it  
can also provide very precise measurements of a cell's position.
	
Optical tweezers use the tiny force of a beam of light from a laser  
to push around and control tiny objects, from cells to plastic beads.  
They usually work on a glass surface mounted inside a microscope so  
that the effects can be observed.

But silicon chips are opaque to light, so applying this technique to  
them not an obvious move, the researchers say, since the optical  
tweezers use light beams that have to travel through the material to  
reach the working surface. The key to making it work in a chip is  
that silicon is transparent to infrared wavelengths of light - which  
can be easily produced by lasers, and used instead of the visible  
light beams.

To develop the system, Lang and Appleyard weren't sure what thickness  
and surface texture of wafers, the thin silicon slices used to  
manufacture microchips, would work best, and the devices are  
expensive and usually available only in quantity. “Being at MIT,  
where there is such a strength in microfabrication, I was able to get  
wafers that had been thrown out,” Appleyard says. “I posted signs  
saying, 'I'm looking for your broken wafers'.”
After testing different samples to determine which worked best, they  
were able to order a set that were just right for the work. They then  
tested the system with a variety of cells and tiny beads, including  
some that were large by the standards of optical tweezer work. They  
were able to manipulate a square with a hollow center that was 20  
micrometers, or millionths of a meter, across - allowing them to  
demonstrate that even larger objects could be moved and rotated.  
Other test objects had dimensions of only a few nanometers, or  
billionths of a meter. Virtually all living cells come in sizes that  
fall within that nanometer-to-micrometers range and are thus subject  
to being manipulated by the system.

As a demonstration of the system's versatility, Appleyard says, they  
set it up to collect and hold 16 tiny living E. coli cells at once on  
a microchip, forming them into the letters MIT.

The work was supported by the Biotechnology Training Program of the  
National Institutes of Health, the W.M. Keck Foundation, and MIT's  
Lincoln Laboratory.

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Written by David Chandler, MIT News Office