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Optical tweezers for nanotechnology

A nanotech version of the optical tweezers traditionally used to manipulate micrometer-scale objects manipulates objects at the 200-nm scale. From nanotechweb.org, written by Belle Dumé (requires free registration) “Nanotweezers trap tiny objects

Researchers have made the first nano-optical tweezers. The devices, which are based on “nanopillars”, offer many advantages over traditional optical tweezers and can trap and move objects on the nanoscale. The breakthrough result opens the way to manipulating fragile biological cells and making structures from nanoscale building blocks.

Traditional optical tweezers, which have been around for decades, are one of the most important modern-day tools in biology, physics and chemistry. They work by trapping micron-scale objects near the focus of a laser beam. The technique allows objects to be picked up and moved to another place using just light.

Although scientists have used optical tweezers to trap nanoscale objects before, this required high laser powers, which can damage or even destroy the object in question. Now, Alexander Grigorenko and colleagues at the University of Manchester in the UK have made nanoscale optical tweezers that overcome this problem. The new devices have a much bigger trapping force and provide significantly smaller trapping volumes for much less laser power than employed in ordinary optical tweezers.

Nanotweezers

The secret behind the new device is that it exploits “virtual” photons to squeeze the trapping volume beyond the diffraction limit of the light being used. It also quenches Brownian motion of trapped nanoparticles by almost an order of magnitude compared to conventional optical tweezers operating under the same trapping conditions. Brownian motion is a common problem as particles get smaller, which makes them difficult to catch.

The nanotweezers are based on a nanostructured substrate comprising a regular array of nanopillar pairs. These are relatively easy to make using conventional electron-beam lithography. The gaps between the nanopillars effectively act as the tweezer traps.

The research was published in Nature Photonics [abstract].
—Jim

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