WASHINGTON, D.C.--Researchers have created a trap capable of immobilizing objects as small as a single virus or molecule of DNA. The technology may help scientists better study such objects in their native states.
The trouble with spying on small particles in solution is that they jitter from random bombardment by molecules in the surrounding liquid. Scientists currently use laser-based methods such as optical tweezers to hold onto such particles. But to study molecules smaller than about 200 nm using optical tweezers, the researchers have to attach the molecules to beads large enough for the tweezers to grasp, which can twist the molecules out of shape.
At the AAAS meeting here Thursday, chemist W. E. Moerner and graduate student Adam Cohen of Stanford University unveiled a trap that counteracts Brownian motion of 5 and 200 nm particles in solution. The Anti-Brownian Electrophoretic (ABEL) trap grabs individual fluorescent (or fluorescent-dye-tagged) particles as small as 5 nm in water. A microscope and high speed digital camera record every kick that the solvent gives the glowing nanoparticle. A computer then instructs four tiny pumps to deliver an equal and opposite kick to the nanoparticle by pushing and pulling the liquid.
"Basically you inject a sample of whatever you want to trap, and within a few minutes you're grabbing and manipulating individual DNA molecules, viruses, fluorescent nanoparticles, or whatever," explains Cohen. It's even gentle enough to restrain squishy biopolymers without rendering them kaput, he adds.
Physicist Kristian Helmerson at the National Institute of Standards and Technology in Gaithersburg, Maryland says that trapping nanoparticles in their native state will allow researchers to study how molecules like RNA change shape. If the tool helps researchers to understand proteins and RNA better, he says, scientists may be able to design more effective drugs.
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