Chameleon-style skin can tell you when seafood spoils

Worried those prawns in your fridge might be past their prime? It’s science to the rescue, with a new artificial colour-changing material that mimics the abilities of chameleon skin to change colour when exposed to vapours released by the microbes in spoiled fish.

The new material, designed by scientists from China and Germany and detailed in the journal Cell Reports Physical Science, contains luminogens – molecules that make crystals glow – which are organised into core and shell hydrogel layers. 

The team say their new material could be applied to a range of contexts beyond the home fridge, including robotics.

“In the near future, we plan to utilise the developed chameleon skin-like core-shell hydrogels to prepare biomimetic soft camouflaging skins, which can be used to mimic the diverse colour-changing functions of living organisms’ skins and to help achieve desirable active camouflage, display and alarm functions in robots,” says Tao Chen, a professor at the Ningbo Institute of Materials Technology and Engineering at the Chinese Academy of Sciences and an author of the study.

While scientists have long sought a way to create soft materials that can fluctuate between a range of colours, synthetic materials are rarely able to change colour with the ease of chameleon skin. 

The authors of the new paper attribute their success to the multi-layered structure of their hydrogel, which mimics the two-layered structure of panther chameleon skin that can fluctuate between a vast range of colours.

The researchers designed the luminogen ‘skin’ from the inside out, by first synthesising a red-fluorescent core hydrogel. This hydrogel was incubated in aqueous Europium solutions, and then incubated in a growth solution containing sodium alginate and response blue/green fluorescent polymers. Spontaneous diffusion of Europium ions from the core hydrogel into the surrounding solution triggered the formation of blue and green hydrogel layers.

The resultant, multi-layered structure can change from red to blue to green, depending on changes in temperature and pH, and the researchers believe the emission colour of the blue-green layers could be adjusted, enabling it to display colours from almost the full spectrum.

The team then tested their material by sealing test strips in boxes with fresh fish for 50 hours: the test strip stored with seafood at lower than -10°C changed only slightly from its original red, while the strip stored with seafood at 30°C changed to a green hue, indicating that the fish had spoiled.

The new material is a prime example of biomimicry, a process by which scientists imitate or emulate quirks found in animals or plants and incorporate them into new technologies. Bio-inspiration is predicated on the fact that most design problems have likely been confronted by natural selection at some point during more than 3-billion-years of evolution of life on Earth.

Other examples of bio-inspired technologies include the nose of the Japanese bullet train, which mimics the way the beak of a kingfisher absorbs impact when the bird plunges into water at high speeds, or Velcro, which mimics the hooks that latch the seeds of some plants onto animal fur, and thereby disperse them. 

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