Butterfly wings used to make bank notes

 
Scientists at Cambridge University have found a way to mimic the colours on tropical butterfly wings, which could be used to make bank notes and credit cards far harder to forge.

The team made structurally identical copies of the scales on wings, which create the same iridescent colour when light bounces off them.
Mathias Kolle, of Cambridge University, said the amazing discovery was like unlocking one of nature's secrets.

'These artificial structures could be used to encrypt information in optical signatures on banknotes or other valuable items to protect them against forgery,' he said.
'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.'
Mr Kolle working with Professor Ullrich Steiner and Professor Jeremy Baumberg, 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.

Because of their shape and the fact they are made up of alternate layers of cuticle and air, these structures produce intense colours when light bounces off them.

Mr Kolle and his colleagues used a combination of nanofabrication procedures to make structurally identical copies of the butterfly scales, and these copies produced the same vivid colours as the butterflies' wings. Nanofabrication is used to create incredibly small devices which are measured in nanometres. One nanometre is equivalent to a millionth of a millimetre.
'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,' he 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 optimise our optical structures.'
 
The butterfly may also be using its colours to encrypt itself, appearing one colour to potential mates but another colour to predators.
Mr 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.