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17 April 2014 12:48 pm ,
Vol. 344 ,
Officials last week revealed that the U.S. contribution to ITER could cost $3.9 billion by 2034—roughly four times the...
An experimental hepatitis B drug that looked safe in animal trials tragically killed five of 15 patients in 1993. Now,...
Using the two high-quality genomes that exist for Neandertals and Denisovans, researchers find clues to gene activity...
A new report from the Intergovernmental Panel on Climate Change (IPCC) concludes that humanity has done little to slow...
Astronomers have discovered an Earth-sized planet in the habitable zone of a red dwarf—a star cooler than the sun—500...
Three years ago, Jennifer Francis of Rutgers University proposed that a warming Arctic was altering the behavior of the...
- 17 April 2014 12:48 pm , Vol. 344 , #6181
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Sifting with Light
20 July 2005 (All day)
A team of researchers has invented a versatile and powerful technique that uses light and electrical force to pick up and sort thousands of delicate microscopic objects at once. Such a tool has multiple biological and physical applications, such as fetal screening or assembling nanocrystals.
The new technique is actually a hybrid of two existing methods used to sort tiny objects: optical "tweezers" and dielectrophoresis, or DEP. Optical tweezers resemble a Star Trek–type tractor beam: A focused beam of light creates an optical trap that attracts and holds microscopic objects as small as a single atom. DEP achieves similar control over tiny particles by inducing a charge in them with a magnetic field and then collecting them, like a magnet picking up iron filings.
Both techniques have drawbacks, however. Optical tweezers, though versatile, can only move objects within a small area at one time, while DEP requires an extensive setup and a high-powered laser that could damage delicate cells. But by combining elements of each method, electrical engineer Ming Wu and his colleagues at the University of California, Berkeley, have invented a device that needs a much less intense light source and can be easily reconfigured for various uses.
Rather than a tractor beam or a magnet, Wu's "optoelectronic tweezers" work more like a photocopier. The light source projects an optical pattern onto a photoconductive layer, turning electrodes in the layer "on" so that they generate a DEP field. The field then draws particles or cells suspended in liquid above the slab into the desired patterns. Such high-resolution control means the device can create numerous "traps" and move thousands of particles at once. The team describes its method in the 21 July issue of Nature.
"I think this is fantastic," says David Grier, a physicist at New York University who works on holographic optical trapping. He says the technique has potential to improve the efficiency of such delicate, difficult procedures as cell sorting and the precise tailoring of nanomaterials. There's also great potential for marrying this new method with existing optical techniques that have other capabilities, such as manipulating objects in three dimensions, he adds.