Researchers demonstrate a new type of optical tweezer

Feb 25, 2008
Microfabricated Fresnel Zone Plate Optical Tweezer
(a). Photograph of microfabricated Fresnel Zone Plate optical tweezer, consisting of concentric gold rings (50 nm thick) on a microscope slide. The Zone Plate outer diameter is 100¼m, and the focal length is 8¼m. (b). CCD camera image of fluorescent bead (2¼m diameter) trapped in Zone Plate focus. Credit: Ken Crozier, Harvard School of Engineering and Applied Sciences

Researchers at the Harvard School of Engineering and Applied Sciences (SEAS) demonstrated a new type of optical tweezer with the potential to make biological and microfluidic force measurements in integrated systems such as microfluidic chips. The tweezer, consisting of a Fresnel Zone Plate microfabricated on a glass slide, has the ability to trap particles without the need for high performance objective lenses.

The device was designed, fabricated, and tested by postdoctoral fellow Ethan Schonbrun and undergraduate researcher Charles Rinzler under the direction of Assistant Professor of Electrical Engineering Ken Crozier (all are affiliated with SEAS). The team's results were published in the February 18th edition of Applied Physics Letters and the researchers have filed a U.S. provisional patent covering this new device.

"The microfabricated nature of the new optical tweezer offers an important advantage over conventional optical tweezers based on microscope objective lenses," says Crozier. "High performance objective lenses usually have very short working distances -- the trap is often ~200 mm or less from the front surface of the lens. This prevents their use in many microfluidic chips since these frequently have glass walls that are thicker than this."

The researchers note that the Fresnel Zone Plate optical tweezers could be fabricated on the inner walls of microfluidic channels or even inside cylindrical or spherical chambers and could perform calibrated force measurements in a footprint of only 100x100μm.

Traditional tweezers, by contrast, would suffer from crippling aberrations in such locations. Moreover, in experimental trials, the optical tweezers exhibited trapping performance comparable to conventional optical tweezers when the diffraction efficiency was taken into account.

The researchers envision using their new tweezer inside microfluidic chips to carry out fluid velocity, refractive index, and local viscosity measurements. Additional applications include biological force measurements and sorting particles based on their size and refractive index. Particle-sorting chips based on large arrays of tweezers could be used to extract the components of interest of a biological sample in a high-throughput manner.

Source: Harvard University

Explore further: Researchers find first direct evidence of 'spin symmetry' in atoms

add to favorites email to friend print save as pdf

Related Stories

Robotics goes micro-scale

Apr 17, 2014

(Phys.org) —The development of light-driven 'micro-robots' that can autonomously investigate and manipulate the nano-scale environment in a microscope comes a step closer, thanks to new research from the ...

Faster testing of new pharmaceuticals

Jan 02, 2014

To improve medical treatment, researchers test new drug ingredients on biological cells. By combining two microscopy techniques, the time required for testing can be reduced by 50 to 80 percent. And far fewer ...

Researchers advance the art of drug testing

Aug 27, 2013

On a rectangular chip slightly smaller than a person's finger, two scientists and an engineer are writing what they hope will be the blueprint for the future of drug testing.

Recommended for you

Water window imaging opportunity

2 hours ago

Ever heard of the water window? It consists of radiations in the 3.3 to 4.4 nanometre range, which are not absorbed by the water in biological tissues. New theoretical findings show that it is possible to ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

superhuman
not rated yet Feb 25, 2008
>"High performance objective lenses usually have very short working distances -- the trap is often ~200 mm or less from the front surface of the lens. "
micrometers i presume not millimeters