April 24, 2015
European Coatings reported on the development by researchers at Northwestern University, who have invented fluorescent inks that “could be used as multi-coloured barcodes for consumers to authenticate products” and avoid using counterfeits. The ink is said to be “very difficult for counterfeiters to mimic”, and can be used in a standard inkjet printer to create barcodes or QR codes for “proof of authenticity”.
The inks can be made in “single colours or as multicolour gradients”, and depend on the “amounts and interaction of three different ‘ingredient’ molecules”, providing a “built-in ‘molecular encryption’ tool”. Even a “tiny tweak” to the composition of the ink would result in a “significant colour change”, and by taking a photo of the barcode on a smartphone camera with UV light, any user would be able to tell “if the item is real”.
Manufacturers can control the recipe of the ink, which is what would make it “virtually impossible” for counterfeiters to imitate, and even the ink’s inventors “would not be able to reverse engineer the process without a detailed knowledge of the encryption settings”. The researchers “stumbled across” the ink “serendipitously”, with the composition of the ink including cyclodextrin (a sugar), a “competitive binding agent” and a molecule called heterorotaxane.
The heterorotaxane’s fluorescence “changes along a spectrum of red to yellow to green”, and an “infinite number of combinations can be defined”. It’s this combination, and the interaction with the other parts of the ink, that causes the colour change, which is “difficult to predict” and presents the ink’s security as an anti-counterfeiting measure. The ink is also sensitive “to the surface to which it is applied”, so different paper types can be identified.
The authentication of the ink can be achieved by “wiping some wet authentication wipes on top of the fluorescent image”, which causes the colours to change “under UV light”. Researchers involved in the discovery said the “smart technology […] allows people to create their own security code by manually setting all the critical parameters. One can imagine that it would be virtually impossible for someone to reproduce the information unless they knew exactly all the parameters”.
Sir Fraser Stoddart from Northwestern University, the senior author of the study, added: “We have introduced a level of complexity not seen before in tools to combat counterfeiters. 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.
“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.”
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