Thanks to what looks like a little square of jelly, you could tell your milk has gone bad without even opening the (gross-smelling) container. The gel is actually a nanorod-embedded smart tag that changes from red to green, mimicking the growth of bacteria in milk without touching it.
Chinese scientists made the gel with tiny gold and silver nanorods, along with some vitamin C, acetic acid, lactic acid, and agar. "The gold nanorods are naturally red," explains CBS News, "and over time, the other compounds like silver gradually deposit onto the gold nanorods, forming a silver shell layer that alters the shape and composition of the nanorods, a process that ultimately changes their colour."
The gel, which only costs a tenth of a penny to make, also responds to temperature. It turns green faster in conditions where bacteria might grow faster. The team's initial design mimics E. coli in milk, though they hope to tweak the synchronisation so that it works for canned foods and medication as well. They presented the findings at the American Chemical Society's current meeting in Dallas.
Unfortunately, this smart tag currently displays red for "good" and green for "bad," which, well, might seem a counterintuitive. Am I being picky or do these colour design decisions really matter? [American Chemical Society via CBS News]
Top image via American Chemical Society/YouTube