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Bright, vivid natural colors found in nature may allow for more secure bank notes and credit cards.
Iridescent colors displayed on beetles, butterflies and other insects have long fascinated 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 the result of light bouncing off microscopic structures on the insects’ wings.[private]
The Indonesian Peacock or Swallowtail butterfly (Papilio blumei), whose wing scales consist of intricate, microscopic structures that resemble the inside of an egg carton, fell under the investigative eye of Mathias Kolle, a scientist who worked with Professor Ullrich Steiner and Professor Jeremy Baumberg of the University of Cambridge in the UK.
Because of their shape and the fact they consist of alternate layers of cuticle and air, these structures produce intense colors.
Using a combination of nanofabrication procedures, including self-assembly and atomic layer deposition, Kolle 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,” Kolle said.
“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.”
Being able to mimic these butterfly colors has could boost 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.
In nature, the butterfly may also be using a form of encryption with its colors. It shows one color to potential mates but another to predators.
“The shiny green patches on this tropical butterfly’s wing scales are a stunning example of nature’s ingenuity in optical design,’ Kolle said. “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 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.”[/private]

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