The photonic crystal ink changes colour from green to red or yellow in response to chemical vapours © ACS 
 
 Simply breathing on money could soon reveal if it's the real deal or counterfeit thanks to a beetle-inspired ink that reversibly changes colour in response to humidity . The photonic crystal ink developed by Chinese researchers can produce unique colour changing patterns on surfaces with an inkjet printer system, which would be extremely hard for fraudsters to reproduce. The work also shows promise for other applications including displays and wearable sensors. 
 
 The ability of photonic crystals to control the flow of light makes them a suitable material for diverse applications including optical communications, biosensors and solar cells. Most of the research over the past 25 years, however, has used expensive high precision tools developed by the microelectronics industry to create their desirable properties. 
 
 Inkjet printing of photonic crystals onto a surface is cheaper, but previous efforts have struggled to integrate responsive photonic crystal inks into such a system. Now, Ling Bai and Zhongze Gu and colleagues at Southeast University in Nanjing, China, have developed a photonic crystal ink that mimics the way Tmesisternus isabellae – a species of longhorn beetle – reversibly switches its color from gold to red according to the humidity in its environment. 
 
 This color shift is caused by the adsorption of water vapour in their hardened front wings, which alters the thickness and average refractive index of their multilayered scales. To emulate this, the team made their photonic crystal ink using mesoporous silica nanoparticles, which have a large surface area and strong vapour adsorption capabilities that can be precisely controlled. 
 
 Using the ink in an inkjet printer, the researchers produced complex patterns on rigid and flexible materials and showed that their colour can be reversibly and precisely controlled – shifting from green to red or yellow for example – in response to nitrogen and ethanol vapours. They even saw patterns change colour simply in response to breathing on them. 
 
 Bai was surprised at how precisely they could control the colour and that the patterns remained intact after being bent several times. 'This technology allows for high resolution, high precision, fast speed, large scale preparation of photonic crystal patterns,' says Bai. 'Patterning of photonic crystals is critical for the realisation of photonic crystal displays and for designing the special functions of photonic crystal optical devices.' 
 
 'It is particularly refreshing to see simple techniques such as inkjet printing being used to such great effect,' says Thomas Krauss who investigates photonic crystals at the University of York. 'Being able to create highly functional photonic crystals by low-cost techniques is important for commercial applications, and I believe that the type of flexible and scalable technology demonstrated here has a great future.' 
 
 'We think the ink's multiple security features may be useful for antifraud applications, however we think the technology could be more useful for fabricating multiple functional sensor arrays, which we are now working towards,' adds Bai. 

 The war on counterfeit products is fought using highly detailed printing, watermarks, and even holograms on packaging, but the latest weapon will also include your breath. Researchers at the University of Michigan and in South Korea have developed a thin film featuring invisible images and features only revealed when blasted with humid air, made using a sophisticated manufacturing process that's hard to duplicate. 
 
 Designed to help combat counterfeit drugs, which harm over 700,000 people every year, the new film—made from a specially developed blend of polyurethane and an adhesive—is covered in microscopic pillars on the surface which serve to completely hide images or words printed on the underside of the material. But when you breathe on it, those tiny pillars temporarily trap moisture, which results in the secret image being revealed. 
 
 The machinery needed to create the film is incredibly sophisticated—and expensive—which will make it very difficult for counterfeiters to reproduce. But once a template has been created, labels can be mass-produced on the cheap, making this a financially viable way for drug manufacturers to verify their products. 
 
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 And there's no reason this anti-counterfeiting measure has to only be used for drug packaging. When was the last time you bought a product that wasn't wrapped in some kind of plastic? One day you might be able to verify the authenticity of everything from Blu-ray movies, to electronics, to even currency, with a few deep breaths. [University of Michigan]
– Scientists are working on an easier way to detect counterfeit money—and they have beetles to thank for it. The system, which would allow people to reveal counterfeit cash by breathing on it, is based on the ability of a longhorn beetle species to change color based on local humidity, Chemistry World reports. Researchers in China are working on an inexpensive inkjet printing technology that works similarly; the ink adsorbs nearby vapors, including those in our breath, and changes color in response. "It is particularly refreshing to see simple techniques such as inkjet printing being used to such great effect," says an outside expert. Comparable research appeared a few months ago, when scientists in Michigan and South Korea revealed a film which, when touched by breath, reveals images or words. That technology could be used to fight the creation of items like fake passports, Wired reported; blowing on the passport could make a special logo appear, for instance. While it's expensive and difficult to create the equipment behind the film—perhaps deterring counterfeiters—it's cheap to produce the stuff once the gear is up and running, Gizmodo reported. (Perhaps that could help stop the likes of this counterfeiting mom.)