The film is made from a commercially available polyester, which is mixed with a cheap and readily available stilbene dye known as BBS. BBS complies with US Food and Drug Administration regulations, so could be used in food packaging, said Pucci. It forms small aggregates throughout the polymer film, which have a green luminescence under UV light. When the film is stretched or deformed, the BBS aggregates are pulled apart and the molecules stop interacting, turning the luminescence blue. Temperature changes also affect the aggregation and shift the luminescent output of the film.
Christoph Weder, a pioneer in smart polymers at Case Western Reserve University in Cleveland, US, said he was 'thrilled' by the new work. 'Pucci [has] shown that the general concepts can be extended to commercially available dyes that are rated as food-compatible, which is an important achievement from a technological point of view,' he said.
Pucci said his next challenge is to develop composite films made entirely from food-grade materials, and films with a wider activity. 'In my opinion the future of this field is based on the formulation of nanostructured sensors sensitive to a broad range of external stimuli,' said Pucci.