'Invisibility stickers' to help troops evade detection in dark

Researchers have developed squid-inspired 'invisibility stickers' that could one day help soldiers evade detection in the dark, even when sought by enemies with tough-to-fool infrared cameras.
Using a protein that is key to squid's camouflaging abilities, scientists designed 'invisibility stickers' to help soldiers disguise themselves.
"Soldiers wear uniforms with the familiar green and brown camouflage patterns to blend into foliage during the day, but under low light and at night, they're still vulnerable to infrared detection," said Alon Gorodetsky at the University of California at Irvine (UCI).
"We've developed stickers for use as a thin, flexible layer of camo with the potential to take on a pattern that will better match the soldiers' infrared reflectance to their background and hide them from active infrared visualisation," Gorodetsky said.

Squid skin features unusual cells known as iridocytes, which contain layers or platelets composed of a protein called reflectin.
The animal uses a biochemical cascade to change the thickness of the layers and their spacing. This in turn affects how the cells reflect light and thus, the skin's colouration.

Gorodetsky's group coaxed bacteria to produce reflectin and then coated a hard substrate with the protein. To induce structural - and light-reflecting - changes just like those of iridocytes, the film needed some kind of trigger.
An initial search revealed that acetic acid vapours could cause the film to swell and disappear when viewed with an infrared camera. But these conditions would not work for soldiers in the field.

So Gorodetsky fabricated reflectin films on conformable polymer substrates, effectively sticky tape one might find in any household.
This tape can adhere to a range of surfaces including cloth uniforms, and its appearance under an infrared camera can be changed by stretching, a mechanical trigger that might more realistically be used in military operations.
Although the technology isn't ready for field use just yet, Gorodetsky envisions soldiers or security personnel could one day carry in their packs a roll of invisibility stickers that they could cover their uniforms with as needed.
"We're going after something that's inexpensive and completely disposable. You take out this protein-coated tape, you use it quickly to make an appropriate camouflage pattern on the fly, then you take it off and throw it away," Gorodetsky said.

Gorodetsky's team is yet to figure out how to increase the brightness of the stickers and get multiple stickers to respond in the same way at the same time, as part of an adaptive camouflage system.
The work will be presented at the 249th National Meeting & Exposition of the American Chemical Society (ACS) in Denver.