Monday, February 13, 2012

Bionic butterfly wings are ultimate heat sensors

Feeling the heat (<i>Image: Patrick Landmann/Science Photo Library</i>)
Feeling the heat (Image: Patrick Landmann/Science Photo Library)

Move over spider silk. Butterfly wings are the new "it" material of the animal kingdom, doubling up as ultra-sensitive heat sensors.
Morpho butterfly wings are iridescent thanks to rows of tiny tree-like structures on their surfaces. Light reflecting off each micrometre-long branch and trunk interferes, producing shimmering colours.
Now Andrew Pris at General Electric's Global Research Center in Niskayuna, New York, and colleagues say those same "Christmas trees" make excellent heat sensors.
When heat, or infrared radiation, hits the trees, the chitin they are made from expands. This increases the distance between the branches and trunks, shifting the wavelength of light they reflect perceptibly.
To boost the wings' sensitivity, the researchers coated samples with a layer of heat-absorbing carbon nanotubes. The coated wings could reveal temperature differences of just 0.018 °C.

Miniaturised beauty

"The beauty of the system described in the paper is its outstanding miniaturisation," says Helmut Schmitz of the University of Bonn in Germany.
The distances between the tree trunks determine the sensors' spatial resolution. At less than a micrometre, this resolution is more than 20 times as sharp as existing detectors. The trees' diminutive size, along with chitin's properties, also means they heat up and cool down very quickly, allowing them to respond to small and fleeting changes in temperature, says team leader Radislav Potyrailo, also at General Electric.
One day, Morpho-inspired sensors could detect inflamed areas in people, or points of friction in machines, the team say.
Does Potyrailo think physics has now bested the butterfly? Not at all, he says: "We can maybe touch one aspect of their performance, but other aspects are still quite remarkable."

Journal reference: Nature Photonics, DOI: 10.1038/nphoton.2011.355

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