28 June 2007

Molecular torch sheds light on cells

Cosmos Online
Researchers have created the world's tiniest artificial light source. The nanowire 'torch' may pave the way for remarkably high resolution imaging of individual cells and molecular structures.
Molecular torch sheds light on cells

A scanning electron micrograph image of potassium niobate nanowires with the length of a micrometre (one millionth of a metre) marked for scale. Credit: Nature/Yang et al.

SYDNEY: Researchers have created the world’s tiniest artificial light source. The nanowire ‘torch’ may pave the way for remarkably high resolution imaging of individual cells and molecular structures.

The technology is also stable in physiological conditions, overcoming what has so far been a major obstacle to imaging objects at the molecular scale, which are smaller than the wavelength of visible light.

The use of nanowires as a light source has “a wide range of potential applications in physics, chemistry, materials science and biology,” said the authors behind the technology in a study published this week in the British journal Nature.

Let there be nanowire

The research team, lead by Peidong Yang from the University of California, in Berkeley, U.S., are leading lights in the new field of bio-nanophotonics, which is the search for ways to illuminate nature’s tiniest scales with the help of nanotechnology.

To create the nanotorch, Yang’s team built nanowires – which are rods of molecules built on a vanishingly small nanometre (10-9 m) scale – from potassium niobate, a material with can convert light from one wavelength into another.

Their experiment relied on a technology known as optical tweezers, which involves using a focused laser beam to hold and manipulate microscopic objects such as nanowires.

By using laser light in the infrared wavelength as their ‘tweezers’, Yang and his team were able to scan a potassium niobate nanowire over a test structure, while also using the nanowire to absorb the infrared light and then convert and reemit it as visible light. The end result was an image of the test structure with sub-wavelength resolution.

Yang and colleagues’ experimental set-up requires no electrodes or conventional electronic wiring, which means probes can be placed close to living tissue with minimum damage to the sample.

Cellular snapshots

“This is pretty cool stuff,” commented James Schuck, who works at the Imaging and Manipulation Facility at California’s Lawrence Berkeley National Laboratory. “Because optical trapping [manipulating something with optical tweezers] typically takes place in liquid media, this imaging technique is perfectly suited for studying biological cell samples.”

Light sources that require electricity are no good in liquid media, as they conduct the charge, potentially damaging living cells.

“What’s more, due to the nature of optical trapping, many individual nanowire traps can be created at once, allowing for massively parallel, and therefore fast and large-scale, imaging with high resolution,” said Schuck who is not a member of the research team behind the discovery.

All of this means that the prospect of scientists zooming down to the molecular level of a cell and taking snapshots of proteins, DNA and other biomolecules is no longer a pipedream. “I call it single cell endoscopy,” said Yang.

While Yang believes the most exciting aspect of the work is it’s potential as a bio-imaging tool, the technique may eventually also find uses in advanced information technology and cryptography, he said.


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