If you’ve ever cracked an egg or opened a carton of milk only to find that you’re on the wrong side of the expiration date, these edible stickers being developed at Tufts University could be a metaphorical life saver. The stickers are made of extremely thin gold antennae on a silk protein substrate that’s flexible enough to curve with the shape of the food, and since the substrate turns sticky when wet it adheres firmly without the use of additional adhesives.
Users can scan the sticker-equipped foods with smartphones to see if they’re still safe to eat. Foods at their optimal eating condition will emit an all-clear signal. The chemical changes that take place in foods as they age and spoil trigger a different signal, telling the user via smartphone that he or she should set the banana down and slowly step away.
It might sound silly – after all, a tomato will tell you when it’s past its prime – but long-lasting processed foods like cheese are somewhat harder to read. The system could be invaluable for people who have no sense of smell and can’t simply take a whiff of milk or fruit juice to tell whether it has gone bad.