There’s more to a butterfly wing than meets the eye — as if the eye needed more. Suppose we said there’s more to a Rembrandt than meets the eye and that by studying a Rembrandt painting’s microstructure, we could learn ways to improve surgery or firefighting. Would you believe it?
The Morpho butterfly, a genus of tropical butterflies from Central and South America, shines with a lovely iridescent blue color that delights butterfly aficionados. (Its image adorns the cover of Illustra’s latest documentary, Metamorphosis.) What doesn’t meet the eye is the intricate microstructure that makes the wing’s beautiful tapestry possible. That microstructure — actually, a nanostructure on the order of billionths of a meter — is loaded with market potential.
For proof, go to General Electric’s Global Research Lab in New York, where Dr. Radislav Potyrailo is breathing on a Morpho butterfly wing. An infrared video camera recording the experiment shows the wing color instantly responding from cool blue to magenta. Heat pulses aimed at the wing produce brilliant patches of orange, yellow and white. The research team is demonstrating its new heat sensor that outperforms any thermal imaging system available today. It can detect temperature changes less than 0.18° C in 1/40th of a second (see video).
Inspired by the iridescence of the Morpho butterfly, the team first examined the structure of the wing scales with a scanning electron microscope. They discovered a forest. The scales are composed of arrays of tree-like structures made of chitin that not only refract light, intensifying the blues and canceling out other wavelengths, but also expand and contract with temperature. As they expand, the refracted colors change accordingly.
Building on the work of Pete Vukusic and J. Roy Sambles, who in a Nature paper in 2003 “described the nanometer-scale photonic structures in the wing scales of the Morpho butterfly and the striking blue iridescence that they generate,” Potyrailo realized that the structure should be “strongly influenced by the gas environment surrounding the nanostructures.”1
In 2008, he assembled a research team to investigate the thermal response of butterfly wings. Detailed studies in 2009-2010 showed that “Morpho butterfly wings can serve as low thermal mass optical resonators and rapidly respond to temperature changes with very high sensitivity.” How do they work? “Our team has found that in these resonators, the optical cavity is modulated by its thermal expansion and refractive index change, resulting in conversion of infrared heat into visible iridescence changes.” In short, you can visualize small temperature changes in living color.
They found that by “doping” the wings with single-walled carbon nanotubes, the structures achieved “18-62 mK [milli-Kelvin] noise-equivalent temperature difference and 35-40 Hz heat-sink-free response speed.”2 The paper shows an electron micrograph of the tree-like structure of the wing scales.
In a blog post decorated with the dazzling artwork of the wing structure, Dr. Potyrailo said his team is “very excited” that their five-year research project has just been published in Nature Photonics.2 And that’s just the beginning. Their discovery “guides future conceptually new bio-inspired thermal imaging sensor designs.”
Our next step is to find a way to mimic nature and to design acute and robust chemical sensors that will offer new attractive sensing solutions in the marketplace. That is what we are focused on solving. If successful, it could launch a new direction in the design of highly selective chemical sensors with straightforward colorimetric readout that could replace current complicated sensor arrays. We foresee that this kind of sensor could be in the market within the next five years.1
Thanks to the micro-design on a beautiful insect’s wings, someday we may see many useful applications. A surgeon might be able to visualize precise locations of inflammation. A soldier might wear higher-resolution night-vision goggles. A firefighter might carry a hand-held thermal sensor to avoid danger. A security inspector might have a new way to detect explosives. Your doctor might study a wound’s heat signature for better diagnosis without incisions. (See the GE press release.)
Potyrailo’s work is part of one of the hottest trends in science: biomimetics, which simply means looking to nature for useful designs. His blog post reflects his enthusiasm: “Hello Earth! New technological advances that have been inspired by Nature provide our society with new, advanced products.” New Scientist‘s coverage ends, “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.'”
None of these articles mention evolutionary theory, nor should they. What possible value could a “narrative gloss” about evolution add to the science demonstrated here? Will anyone buy the line that millions of years of aimless, pointless mistakes led to nanostructures on a butterfly wing that engineers marvel at? Biomimetics owes its vitality to the premise of intelligent design, whether the practitioners say so or not: intelligent minds are designing products based on the assumption that nature’s designs are intelligent and worth imitating.
1. Radislav Potyrailo, “Discovery of selective vapor response with nanostructures of butterfly wing scales,” GE Global Research blog “Edison’s Desk.”
2. Pris, Potyrailo et al., “Towards high-speed imaging of infrared photons with bio-inspired nanoarchitectures,” Nature Photonics (2012), doi:10.1038/nphoton.2011.355.
3. GE press release 2/13/2012, “New Butterfly-Inspired Design from GE to Enable More Advanced, Low Cost Thermal Imaging Devices.”
4. YouTube video clip, “GE’s Butterfly-Inspired Design to Enable Advanced, Low Cost Thermal Imaging Devices.”
5. Radislav Potyrailo, “Nanostructures of Morpho butterfly wing scales demonstrate high resolution of temperature changes at high speed,” PrSync, 2/13/2012.
6. Bob Yirka, “Researchers Make Better Heat Sensor Based on Butterfly Wings,” PhysOrg, 2/13/2012.
7. Maggie McKee, “Bionic butterfly wings are ultimate heat sensors,” New Scientist, 2/12/2012.