Acoustic Waves Outshine Lasers for Tiny Tweezers

Physicists and engineers can do some pretty amazing things. For example, when trying to study structures and substances on the molecular level, eventually it becomes necessary to be able to manipulate individual molecules, or even atoms. Needless to say, no tweezers in existence are small enough for the job.

Which is why physicists turned to light.

Yes indeed, there exists such a thing as optical tweezers that use intense beams of focused light to manipulate micrometer-sized – and even nanometer-sized – objects in three dimensions. Pioneered by our own Secretary of Energy Steven Chu, such microscopic manipulations without physically touching a thing are quite the marvel.

Optical tweezers work because the center line of an intensely focused laser beam creates an electric field. So if the particle in question has an electric charge, it will be affected by this field. By combining multiple lasers of differing polarizations, tiny, tiny particles can be moved tiny, tiny distances.

Of course, there are drawbacks.

These forces are too small to manipulate thousands of molecules at a time, say by moving around a tiny organism. Additionally, these powerful lasers suck up a lot of energy, and tend to heat up the samples being manipulated.

Now, scientists from Penn State University (Tony Jun Huang, Stephen Benkovic and co.) seem to have found a different solution that solves some of these problems. Instead of turning to light, they’re turning to sound.

Described in this week’s Proceedings of the National Academy of Sciences (PNAS) is a paper detailing the successful engineering and use of acoustic tweezers. The acoustic tweezers uses ultrasound to create standing surface acoustic waves, which in turn create pressure fields in the liquid medium that holds the thing trying to be moved.

Already, the new device has been tested successfully with C. elegans, a one-millimeter-long roundworm that is an important model system for studying diseases and development in humans. Once tweaked a bit with future developments, the team also believes the tweezers can be used to manipulate items on a nanoscale.

At present, it can handle individual cells, and even individual molecules. And besides being much cheaper to manufacture than optical tweezers, it also uses 10,000,000 times less energy and doesn’t heat up the samples.

Sounds like optical tweezers are a vision of the past.

Excuse the puns.


About bigkingken

A science writer dedicated to proving that the Big Ten - or the Committee on Institutional Cooperation, if you will - is more than athletics.
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