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@Ankita Katdare • 18 Mar, 2014 • 1 like
At the National Meeting & Exposition of the American Chemical Society, a new kind of color-coded smart tags were presented that can tell if the perishable products inside containers are fresh enough for consuming or not. The new smart tags were tested on a carton of milk and they could tell if the milk had turned sour. Be it a bag full of green peas or your medicines, these smart tags will be present on the packaging and will tell the buyer if a product has gone stale without the need to open it. Developed by a Chinese team of researchers, the smart tags possess gel-like consistency and are very cheap to manufacture (less than one cent or approx. $0.002).


Using these tags - both consumers and grocery-store owners can know if the packaged perishable food items are fresh or not. Sometimes, the products are well ahead of the expiry date, but get unduly exposed to higher temperatures, resulting in spoilage. As per the configuration by the research team, the color codes each signify the state of the food inside a packet from 100% fresh to 100% spoiled. So, red, or reddish orange, would mean fresh. Over the time, the tag will turn yellow and later green, which will indicate the food is unfit for consumption.


The researchers tested the smart tags on milk using E. coli - the bacteria responsible for spoiling food as well as causing gastrointestinal problems. At different temperatures, the chemical evolution process was effectively reflected with different colors on the smart tags. It has to be noted here that the tag is made up of tiny metallic nanorods along with Silver chloride and Vitamin C. With 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.

Take a look at the video put together by the American Chemical Society -

The research work is presented in a paper titled - Time–Temperature Indicator for Perishable Products Based on Kinetically Programmable Ag Overgrowth on Au Nanorods at ACS.
Source: Science Daily
@Void Runner • 08 Apr, 2014 Chemical reaction, catalysed by the presence of bacteria? Very interesting! 😀

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