A team from Northwestern University in the US has invented "smart" invisible inks that can be used as multi-coloured barcodes for consumers to authenticate products that are often counterfeited.
Consumers can snap photos with smartphones to see if an item is real in the near future, the researchers added. These inks, which can be printed using an inkjet printer, are invisible under normal light but visible under ultraviolet light.
The inks could be stamped as barcodes or QR codes on anything from banknotes and bottles of whiskey to luxury handbags and expensive cosmetics, providing proof of authenticity.
"We have introduced a level of complexity not seen before in tools to combat counterfeiters," said the study's author, Fraser Stoddart.
"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," he said.
A key advantage is the control one has over the colour of the ink. These inks can be made in single colours or as multi-colour gradients.
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An ink's colour depends on the amounts and interaction of three different "ingredient" molecules, providing a built-in "molecular encryption" tool.
One of the ingredients is a type of simple sugar. Even a tiny tweak to the ink's composition results in a significant colour change.
Counterfeiting is a very big business worldwide, with $650 billion per year lost globally, according to the International Chamber of Commerce.
The new fluorescent inks give manufacturers and consumers an authentication tool that would be very difficult for counterfeiters to mimic.
"This is a smart technology that allows people to create their own security code by manually setting all the critical parameters," the authors noted.
Stoddart's research team, led by Xisen Hou and Chenfeng Ke, stumbled across the water-based ink composite serendipitously.
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.
Details of the fluorescent inks were published in the journal Nature Communications.