Biomimicry of butterfly wing scale structure could cut bank fraud

Cambridge scientists have discovered a way of mimicking the vivid and beautiful colors found on the wings of tropical butterflies in order to lessen the frauds in the future and enhance the security in the printing industry. The findings could find important applications in the security printing industry, helping to make bank notes and credit cards harder to forge.

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

Mathias Kolle, working with Professor Ullrich Steiner and Professor Jeremy Baumberg of the University of Cambridge, studied the Indonesian Peacock or Swallowtail butterfly (Papilio blumei), whose wing scales are composed of complex microscopic structures that resemble the inside of an egg carton. Because of their shape and the fact that they are made up of alternate layers of cuticle and air, these structures produce intense colors.

By 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, and these copies produced the same vivid colors as the butterflies’ wings.

“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”, said Kolle. “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 optimize our optical structures.”

Interestingly, the butterfly may also be using its colors to appear differently to its potential mates and predators. Seen with the right optical equipment, these patches appear bright blue, but with the naked eye they appear green. If its eyes see fellow butterflies as bright blue, while predators only see green patches in a green tropical environment, the butterfly has advantage to hide from predators at the same time as remaining visible to members of its own species.

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

“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”, Kolle said.