British scientists have already looked to principles employed by butterfly wings, as a means of thwarting currency counterfeiters. Now, researchers from China's Southeast University have developed another such technology, that's inspired by a different insect – a color-changing longhorn beetle known as Tmesisternus isabellae.

The beetle's wing cases are covered in long, flat hydrophilic (water-attracting) scales that appear gold when they're dry. When the air becomes humid, however, water droplets are absorbed by those scales and penetrate through to a layer inside of them. That layer swells, changing the way in which the scales reflect light – as a result, they now appear red. Once the scales dry again, they return to their gold coloration.

Using colloidal photonic crystals, the scientists developed an ink that exhibits a similar type of color change when exposed to ethanol vapors. While the crystals themselves are not new, methods of working with them are usually expensive. The new ink, however, can be applied quickly and cheaply to hard or flexible surfaces via an inkjet printer.

The ink can be tuned to a variety of colors, is durable, and – unlike some color-changing polymers, pigments and dyes – won't bleach after prolonged exposure to light or air. Additionally, its unique properties should prove very difficult to copy.

A paper on the research was published this week in the journal ACS Nano.