Light Used to Trap, Move DNA

Cornell University scientists used light to trap DNA and other nanoparticles in moving water. The technology should find itself useful in lab-on-chip devices and other clinical testing tools.
From the National Science Foundation:

Light has been used to manipulate cells and even nanoscale objects before, but the new technique allows researchers to manipulate the particles more precisely and over longer distances.
“At the nanoscale, we can think of light like a series of massless particles called photons,” says Cornell engineer David Erickson, one of the co-authors of the study. “We’ve demonstrated a way to condense these photons down to a very small area and stream them along a special type of waveguide, a device that acts like a nanoscale optical fiber. When pieces of matter, like DNA or nanoparticles, float near these streaming photons, they are sucked in and pushed along with the flow. The effect is sort of like moving a truck by throwing baseballs at it. The trick is that we found a way to have a large number of highly efficient “collisions” between the photons and the nanoparticles, getting them to stay in our device and keep them moving along it.”
Erickson and fellow Cornell engineer Michal Lipson, along with their graduate students Allen Yang, Sean Moore and Bradley Schmidt, and colleagues in Erickson’s and Lipson’s research groups, crafted a wave guide to shunt light into a narrow beam, laying a trap for the DNA and other small pieces of material.
Each of the tiny channels within the waveguide is only 60-120 nanometers (billionths of a meter) wide, thinner than the 1,500 nanometer wavelength of the infrared laser light channeling through them. The channels keep the light waves focused and enhance their ability to interact with the DNA particles, preventing them from flowing by.
The breakthrough is the use of the slot waveguide, which condenses a light wave’s energy to scales as small as the target molecules, overcoming prior limitations caused by light diffraction. Because the waveguide is also a “nanochannel” it can both trap and transport objects using light.
For their experiments, the researchers used water solutions containing either DNA or tiny nanoparticles, washing the fluids over the waveguide microchannels. At a speed of 80 micrometers per second, the system traps less than a fourth of the target particles flowing by, but with smaller channel sizes, slower flows and higher energy lasers, the success rate increases.
“What we’re hoping to do now is better understand some of the underlying physics to see what else might be possible with this approach,” adds Erickson. “Ultimately we imagine being able to take all the ultrafast and highly efficient optical devices that have been developed for communications and other applications over the last 20 years and apply them to the manipulation of matter in different types of nanosystems. Hopefully in the future we can shuttle around individual strands of DNA the same way we now shuttle around light.”

Press release: Nano “Tractor Beam” Traps DNA …
Image: DNA molecules suspended in a stream of water flowing through a nanoscale channel
Watch video from the experiment…