Invisible inks identify fake products from your phone

Scientists in the US have developed sophisticated fluorescent inks which they believe could be used by consumers to spot a fake product just by taking a photo on their smartphone.

Researchers at Northwestern University have come up with inks, which can be printed using an inkjet printer, and are invisible under normal light. However, they can be seen under ultraviolet light and could be stamped as barcodes or QR codes “on anything from banknotes and bottles of whisky to luxury handbags and expensive cosmetics, providing proof of authenticity”.

The inks are formulated by mixing a simple sugar (cyclodextrin) and a competitive binding agent with a molecule known as heterorotaxane,  whose fluorescent colour changes along a spectrum of red to yellow to green, depending upon the way the components come together. Although the sugar is colourless, it interacts with the other components of the ink, thus preventing the molecules from sticking to one another and causing a change in colour that is difficult to predict, according to the scientists, who have published their work in the journal Nature Communications.

‘Formidable challenge to counterfeiters’

This characteristic, the researchers say, “presents a formidable challenge to counterfeiters”.  Sir Fraser Stoddart, senior author of the study, said “we have introduced a level of complexity not seen before in tools to combat counterfeiters”, adding that “our inks are similar to the proprietary formulations of soft drinks. One could approximate their flavour using other ingredients, but it would be impossible to match the flavour exactly without a precise knowledge of the recipe”.

Sir Fraser went on to say that “the rather unusual relationship between the composition of the inks and their colour makes them ideal for security applications where it’s desirable to keep certain information encrypted or to have brand items with unique labels that can be authenticated easily”.

His research team, led by Xisen Hou and Chenfeng Ke, stumbled across the water-based ink composite by chance. A series of “rigorous follow-up investigations unravelled the mechanism of the unique behaviour of the inks” and led the scientists to propose an encryption theory for security printing.