Nakayama et al., Nature, 447 (June 28, 2007)

Tiny torches.
Lithium niobate nanowires could lead to endoscopes capable of scanning within single cells.

Nanoscale Flashlight

Staff Writer

Researchers may soon be able to use a nanoscale flashlight to peer within cells and see everything from DNA to proteins, thanks to a new advance in nanotechnology. In today's Nature, researchers describe a novel nanowire-based light source. Although only tested on nonliving materials so far, the device has the potential to take visible light microscopy where it's never been before: inside cells.

Electron microscopes and scanning probes have long imaged biological structures at the nanoscale, but the electron beams kill the organism. Researchers have struggled to accomplish the same resolution with visible light, a potentially less invasive source. The biggest problem is that diffraction normally makes it impossible to see features much smaller than the wavelength of light used in the imaging. Optics researchers have found a variety of ways around that limit, using light to image features as small as 20 nanometers. Alas, these methods damage or poison cells, which makes them impractical for studying biological structures.

Researchers led by chemist Peidong Yang and biophysicist Jan Liphardt at the University of California (UC), Berkeley, found a friendlier alternative in nanowires made from potassium niobate, a material that has low toxicity and is chemically stable in liquids at room temperature. After synthesizing the nanowires, the researchers grabbed and moved individual nanowires in solution with an infrared laser used to create what's known as an optical trap. Once trapped, the nanowires absorb some of the infrared light and reemit it at a higher frequency of green light. The researchers then scanned their mini green flashlight over a sample of gold lines drawn on glass, to show that they could image features as small as 100 nanometers. The UC Berkeley researchers hope to improve that resolution by further shrinking the dimensions of their nanowires.

"This is really exciting," says Deli Wang, a chemist and nanowire expert at the University of California, San Diego. Down the road, Wang says it might be possible to create arrays of such nanoscale flashlights on chips for biological and chemical sensing. It may also be possible to integrate such tiny lights on scanning probe microscopes to help illuminate biological structures never seen before. "It has a lot of potential," Wang says.

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