Most of us use our noses to determine whether food is safe to eat, and while that method will let you know when something is really bad, it's far from foolproof. A group of scientists in China have developed a far more accurate method, using little smart tags with embedded nanorods to do the sniffing.
Each smart tag is a small corn kernel-shaped lump of material embedded in the wall of the container. The tag contains tiny nanorods that react to the release of microbes in food or medicine. When the food is fresh, the tag is red, but as thing start to spoil, the tag slowly changes to orange, then yellow and finally green. At that point, it's probably best to avoid the food all together, unless you want a serious case of food poisoning. Going by the deep green of the tag on the medicine in the picture, they'd better toss that stuff out.
This approach is far more accurate than a simple expiration date, as it can account for changes in temperature in addition to just the age of the product. For example, if a milk delivery truck has a broken air conditioner on a hot summer day, the tags might all be green before the milk even hits the supermarket shelves. Conversely, milk that is stored perfectly in a dark cool place might still be good days or even weeks after the traditional expiration date.
Lead researcher Chao Zhang from Peking University in Beijing says that the tags will likely cost less than 1/5 of a penny each. They were presented on Monday at a meeting of the American Chemical Society, and while they aren't available yet, the team is currently reaching out to manufacturers.