Butterfly inspires new nanotechnology

If you're lucky enough to visit the tropical forests of central America, you might spot the highly distinctive bright blue wings of a Morpho butterfly. And if you look really carefully, you might see their wings subtly switching colour in response to changes in the chemical make-up of the surrounding air. Now, taking his inspiration from these insects, Tim Starkey, from the University of Exeter, has developed a new form of sensor technology that works the same way, as he explained to Kat Arney...

Tim - Ususally colour is produced in two ways. The most common one is through chemicals. So for example most of your clothes and the things you see around you are created through pigmentation. And that's where light comes in. Some of it is absorbed and what is reflected or transmitted to your eye, you perceive as the colour. These butterflies create colour through structure so they're made up of lots of very thin layers which manipulate light to give you a blue colour.

Kat - What does the structure of these wings look like? How do they look?

Tim - If you were to take one of these butterflies and take a scale off, if you take a cross section and look at these sort of side on, you'll see that this scale contains what look like tiny little Christmas trees which are about a millionth of a meter tall. So, it's like a hundredth of the thickness of a human hair. Within these little structures are reflecting layers. So, it's made up of material which is a protein, much like our fingernails. But it's layered in such a way and its structure exists in such a way that light will come in and the butterfly is optimised to reflect blue colour.

Kat - So, how did these little Christmas trees, these structures change when different gases or different levels of humidity are around?

Tim - What happens is, because of the local chemistry, the vapour in the atmosphere will stick to the Christmas tree in different places. So, for one chemical for example water, it will stick to the top of the Christmas tree preferentially and for a different chemical, maybe methanol or ethanol, or some other nasty thing in our environment would stick in a different way. The actual positioning or the way that these vapours stick to the nanostructure gives rise to these different optical or different colours.

Kat - There are devices being developed that can sense nasty chemicals, different levels of gases in the air, how could you use this observation that the butterfly's wings do change colour in response to these chemicals? I'm assuming that you can't make a sensor just of a butterfly pegged in the middle of it.

Tim - No. So, when the initial study came out, when we realised when we were studying the butterfly, we had some proposals that maybe we should farm these butterflies and turn them into sensors. But we're so very much against that idea because we know we can go one better and make an improvement on nature's design. So, we actually create these nanostructures through special fabrication processes. It's very much like taking a photographic film and exposing it to light to create colour, but we actually do that with electrons to create these very intricate nanostructures.

Kat - What sort of chemicals could they detect? Could they pretty much detect anything you wanted to pick up?

Tim - I think we could actually tune these for different chemical, biological sensing applications. Really, this study shows the principles by which we can do that. Providing we have the correct chemistry and we can create these structures, we can even grow them potentially in the future then you could tune them to many different applications.

Kat - How soon do you think that might be that you could see a working prototype sensor based on these butterfly wings?

Tim - Often, scientists are sort of limited by the scale that you can produce these, so it's fine to produce them in the lab and they work perfectly. But really, it's about making them cost effective and being able to roll them out for mass market. It's a difficult question to answer, but assuming that the techniques by which we can create these continue to improve at the rate they have been recently. Conceivably, things like this could be put into market, possibly in the next few years.