Now, beetle-inspired ink to fight counterfeiting

Inspired by a longhorn beetle, researchers have developed a new colour-changing ink that could thwart counterfeiters and also produce colourful, changing billboards and art displays.
Chinese researchers said the new ink mimics the beetle's colour-shifting ability in a way that would be long-lasting and difficult to copy.
In the journal ACS Nano, Zhongze Gu, Zhuoying Xie, Chunwei Yuan and colleagues explained that some US bills have colour-changing features to help thwart attempts by counterfeiters to make fake money.
But these features based on the chemical structural changes of dyes, pigments or polymers tend to fade when exposed to light and air.

Researchers have been developing a new set of colour-changing materials known as colloidal photonic crystals that are bleach resistant. The methods that use these crystals remain expensive, however.
Inkjet printing is a fast, precise and low-cost alternative, but until now, researchers had not developed the right inks for making such colour-changing and complex patterns.

For inspiration, Gu's team turned to Tmesisternus isabellae, a longhorn beetle that can shift from gold to red and back again, depending on the humidity.
The researchers designed an ink that they can finely tune to change colour, for example, from bright green to yellow or red when exposed to ethanol vapours. It can also return to its original colour.

The ink is also durable, resistant to bleaching when exposed to light and can be applied to hard or flexible surfaces.