researcher from chao zhang of peking university in beijing, china had developed a tiny tag that can replace ordinary expiry date printed on packaging. this colour coded small tag uses nanotechnology for indicating that food and drug are in danger of spoiling. these gellike peking tags are the size of a kernel of corn, inexpensive, safe, and even edible. these tags are made of tiny compounds called nanorods that are made out of gold and silver, but only cost onefifth of a penny each. the color of these gold nanotube is red that is why the researchers don&39t use the more conventional green for fresh. it also contain vitamin c, acetic and lactic acids, and agar which react with nanorods to change their color by reacting to the ambient temperatures around them in a programed fashion. the gold nanorods are naturally red, and over time, the other compounds like silver gradually deposit onto the gold nanords, forming a silver shell layer that alters the shape and composition of the nanorods, a process that ultimately changes their color. this process is programmed to mimic the deterioration of foods based on expiration date, but also spoilage caused by temperature changes. it appear red or reddish orange when 100percent fresh, but over time, they change to orange, yellow and green, which means the food is 100percent spoiled. according to zhang, the tags can be widely programmed to mimic all ambient temperatures, and tell whether or not the product has gone off regardless of what the date on the label says.
