If you have not yet witnessed the wonder of an octopus changing colour instantaneously, then you should go do that right now. We humans are only slowly playing camouflage catch up. A new colour-changing sheet that adapts to the light it senses brings us a tiny step closely to octopi.
The device, presented this week in the journal PNAS, is made of temperature-sensitive dye that appears black at cool temperatures and transparent at higher ones. Popular Mechanics explains how it works:
The top layer of the new device is loaded with a temperature-sensitive dye that appears black at low temperatures and clear at temps above 116 degrees F. This dye-filled layer sits on top of a layer of white reflective silver tiles, an ultra-thin layer of silicon circuits that control the dye's temperature, and a transparent silicone rubber foundation. All together, this stack measures less than 200 microns thick. (The average human hair is 100 microns wide.)
Underneath this flexible sandwich is a base layer containing an array of light-sensing photodetectors. The corners of each dye-filled pixel and silver tile above this photoreceptor layer are notched, creating gaps that are like holes in a mask, allowing light to get through to the photoreceptors so they know how and when to change colour. This adaptive camouflage system can respond to changing patterns of illumination within just one to two seconds.
Black and white is, obviously, quite primitive compared to the amazing capabilities of the octopus. The device also sucks up power and only works at certain temperatures. But John Rogers of the University of Illinois at Urbana — Champaign, who led the study, tells National Geographic this current device is more about proof of principle. To improve on the basic idea, they might swap in components that use electric fields instead of heat to change colour and alternative dyes that appear as a variety of shades.
But for now, seriously, watching an octopus camouflage itself is one of the better ways to spend your afternoon.
Pictures: Yu et al. PNAS