Butterfly wings may help tackle fake note menace

Scientists have discovered a way to mimic the vivid colours on the wings of tropical butterflies, which they claim could help make bank notes harder to forge.

A Cambridge University team, which studied the Indonesian Peacock or Swallowtail butterfly (Papilio blumei), developed structurally identical copies of the scales on wings of the butterflies.

They found that when light bounces off them, the artificial structures created the same iridescent colour as the butterfly wings.

Swallowtail butterfly wing scales are composed of intricate, microscopic structures which resemble the inside of an egg carton.

The findings, published in Nature Nanotechnology, were described by the scientists as unlocking one of nature's secrets.

Lead researcher Mathias Kolle said: "These structures could be used to encrypt information on banknotes 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 pound note or even our passports," he said.

According to the researchers, the bright green wings of the butterfly result from the mixing of the different colours of light that are reflected from different regions of the scales found on the wings of these butterflies.

To find out whether such a mechanism can be made artificially, the scientists used a combination of nanofabrication procedures, including self-assembly and atomic layer deposition, to develop structurally identical copies of the butterfly scales.

They found the artificial structures -- which are very similar to the scales on butterfly wings -- also able to produce the same stunning colours as the butterfly wings when light bounces off them.

"Although nature is better at self-assembly than we are, we have the advantage that we can use a wider variety of artificial, custom-made materials to optimise our optical structures," said Kolle.

The scientists believe that butterflies may also be using their colours to encrypt itself, appearing one colour to potential mates but another colour to predators.

Kolle explained: "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.

"This could explain why the butterfly has evolved this way of producing colour. 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," Kolle added.