Scientists have developed "smart tags" which let consumers know when food has spoiled.
Announced at the American Chemical Society's 247th annual meeting, researchers in China have created an inexpensive, gelatin-like material which changes color to monitor the status of perishable items. From red to orange to green, as food and drink is exposed to temperatures which encourage bacteria growth, the "smart tag" -- added to packaging -- eventually will take on a green hue.
Once it reaches this stage, the product is unlikely to be safe to eat or drink and should be thrown away.
Gold nanorods and silver chloride are embedded within the material which gradually changes color based on time and temperature. Once synchronized to a particular foodstuff, the tag is able to rate food between 100 percent fresh and 100 percent spoiled.
In order to test the theory, the team focused on the amount of E. coli in milk.
Peking University's Chao Zhang, Ph.D., lead researcher of the study said:
"The gold nanorods we used are inherently red, which dictates the initial tag color. Silver chloride and vitamin C are also in the tags, reacting slowly and controllably. Over time, the metallic silver gradually deposits on each gold nanorod, forming a silver shell layer.
That changes the particle's chemical composition and shape, so the tag color now would be different. Therefore, as the silver layer thickens over time, the tag color evolves from the initial red to orange, yellow, and green, and even blue and violet."
It is not just cartons of milk, frozen chicken or eggs that could be tracked using the technology. The tags could also be used for other perishables, including medication.