Gel-based encryption can only be unlocked with key of light and heat

A chemical gel can reveal a secret sequence of numbers if given the right “password” – a combination of heat, light and water. The technology could be used to prevent counterfeiting or in smart labels

By Alex Wilkins

A chemical gel can reveal a secret sequence of numbers if exposed to the right “password” combination of heat, light and water – and it could be used to prevent counterfeiting or in smart labels.

Most methods to prevent counterfeiting goods involve a single physical attribute that is difficult to reproduce, such as hidden threads or watermarks that glow under UV light. An alternative approach is for an object to display an authentication code only if given an input in a certain order.

Now, Weiguo Huang at the Chinese Academy of Sciences in Fujian and his colleagues have adapted a class of molecules called donor-acceptor Stenhouse adducts (DASA), which change from colourful to clear when exposed to visible light. They used DASAs to develop a set of 12 molecules that go from clear to coloured and back again in response to varying levels of heat, light and water.

Huang and his team embedded the altered molecules in a gel and arranged them to create a chemical display, in the shape of an eight seen on digital clocks. Each segment of the eight was made up of different DASAs, enabling different numbers to be produced when only certain DASAs lit up. When the chemical display is exposed to the correct sequence of stimuli for the right amount of time, it outputs a series of numbers as the sequence is run.

The input sequence is specific to the placement of the different DASAs, known only to the display’s creator – so it is encrypted.

Huang hopes the gel could be used in smart labels embedded in things like banknotes, passports and stock certificates or in high-value items that require proof of authenticity.

The technique could be useful for anti-counterfeiting because it is hard to mimic without knowing the chemical composition of the gel display in the original object, says Joakim Andreasson at Chalmers University of Technology in Sweden.

Journal reference: Science Advances, DOI: 10.1126/sciadv.add1980