Butterflies' wings could cut bank fraud

Posted by Emma Woollacott

Banknotes could get a lot prettier, thanks to a new nanotechnology technique which mimics the iridescent colors found on butterflies' wings.

TheUniversity of Cambridge team says the discovery could have important applications in security printing.  
 
Rather than relying on pigments, a butterfly's colors are produced by light bouncing off microscopic structure, a little like the inside of an egg carton, on the insects' wings.
 
Because of their shape, and the fact that they are made up of alternate layers of cuticle and air, these structures produce intense colors.

The team studied the Indonesian Peacock or Swallowtail butterfly (Papilio blumei). Using a combination of nanofabrication procedures – including self-assembly and atomic layer deposition – the scientists made structurally identical copies of the butterfly scales, which produced the same vivid colors as the butterflies' wings.

The discovery has promising applications in security printing, according to co-author Matthias Kolle.

"These artificial structures could be used to encrypt information in optical signatures on banknotes or other valuable items to protect them against forgery. We still need to refine our system, but in future we could see structures based on butterflies wings shining from a £10 note or even our passports," he says.

The butterfly may even be one step ahead on this - 'encrypting' itself by appearing one color to potential mates but another color to predators.
 
"The shiny green patches on this tropical butterfly's wing scales are a stunning example of nature's ingenuity in optical design. Seen with the right optical equipment these patches appear bright blue, but with the naked eye they appear green," says Kolle.

"This could explain why the butterfly has evolved this way of producing color. If its eyes see fellow butterflies as bright blue, while predators only see green patches in a green tropical environment, then it can hide from predators at the same time as remaining visible to members of its own species."