How nature's colours could cut bank fraud

MONDAY, 31 MAY 2010

Mathias Kolle, working with Prof. Ullrich Steiner and Prof. Jeremy Baumberg at the University of Cambridge, studied the Indonesian Peacock or Swallowtail butterfly (Papilio blumei), whose wing scales are composed of intricate, microscopic structures that resemble the inside of an egg carton.

The striking iridescent colours displayed on beetles, butterflies and other insects have long fascinated both physicists and biologists, but mimicking nature's most colourful, eye-catching surfaces has proved elusive. This is partly because rather than relying on pigments, these colours are produced by light bouncing off microscopic structures on the insects' wings.

Using a combination of nanofabrication procedures - including self-assembly and atomic layer deposition - Kolle and his colleagues made structurally identical copies of the butterfly scales, which produce the same vivid colours as the butterflies' wings. According to Kolle: "We have unlocked one of nature's secrets and combined this knowledge with state-of-the-art nanofabrication to mimic the intricate optical designs found in nature."

"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."

As well as helping scientists gain a deeper understanding of the physics behind these butterflies' colours, being able to mimic them has promising potential applications in security printing.

"These artificial structures could be used to encrypt information in optical signatures on banknotes or other valuable items to make 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 ten-pound note or even our passports," he says.

Intriguingly, the butterfly may also be using its colours to encrypt itself - appearing one colour to potential mates but another colour to predators.

Kolle explains: "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."

The results are published in Nature Nanotechnology ^[1].

Written by Katherine Thomas

References:

Mathias Kolle et al., “Mimicking the colourful wing scale structure of the Papilio blumei butterfly,” Nature Nanotechnology 5, no. 7 (2010): 511-515.