Scientists at Tufts University, USA, have created a high-tech sticker that lets you know when a food is edible.  The sticker is made with a thin layer of gold antennae embedded in a purified  silk film, and it’s flexible enough to be stuck onto any surface. When the  sticker is scanned by a smartphone, it can let you know if a banana has reached  its optimal ripeness, or if an egg or the milk has gone bad.

The smart sticker is able to pick up on the chemical changes when food ripens  or rots, and emit a different electromagnet signal when monitored with a reader.  Unlike existing RFID technology, these stickers are actually edible as well.