Although the best-before dates on our foods may stop us from eating spoiled items, they can also cause us to toss out food that's really still good. New phone-powered labels could help, by notifying users when the food is actually starting to go "off." The prototype labels are being developed by a team at Britain's Imperial College London, led by Dr. Firat Güder. Scientifically known as "paper-based electrical gas sensors" (PEGS), they're made mainly of readily-available cellulose paper, onto which are printed conductive carbon-ink electrodes. dded to a disposable NFC (near-field communication) chip and then integrated into food packaging, the labels' paper fibers take in water vapor given off by the food. If water-soluble gases associated with food spoilage are present – gases such as ammonia, trimethylamine or carbon dioxide – the electrical conductance of the paper increases, with the extent of the increase determined by how much gas is present.

[Source: New Atlas. 5 June 2019. Ben Coxworth]