A colour coded tag that is smaller than a finger nail and costs a fraction of a penny has been unveiled.
Invented by Chao Zhang of Peking University in Beijing they can be customised for many perishable foods.
They start off red and as the food becomes unsafe they gradually turn green.
The patch is currently set to track the growth of E Coli in milk but Chao Zhang said it “can be re-programmed to mimic almost all ambient-temperature deterioration processes in food”
The sensors were announced recently at a meeting of the American Chemical Society and their inventor wants to hold talks with food companies.