Mathias Kolle, working with Ullrich Steiner Jeremy Baumberg, both professors at the University of Cambridge, studied the Indonesian peacock or Swallowtail butterfly, whose wing scales are composed of intricate, microscopic structures. Because of their shape and the fact that they are made up of alternate layers of cuticle and air, these structures produce intense colours.

Kolle and his colleagues made structurally identical copies of the butterfly scales, with the help of nanofabrication. These copies produced the same vivid colours as the butterflies' wings. "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.

"These artificial structures could be used to encrypt information in optical signatures on bank notes 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 pound note or even our passports," Kolle says. Intriguingly, the butterfly may also be using its colours to encrypt itself - appearing one colour to potential mates but another colour to predators. The results were published in Nature Nanotechnology.