Scientists at the Massachusetts Institute of Technology in the United States have developed a food packaging made of silk that changes color when exposed to decaying food and can quickly degrade in the soil. Relevant research papers were published in the latest issue of ACS Nano, a journal of the American Chemical Society. Research leader Benedetto Marilli stated that the date labels affixed to perishable foods cannot accurately predict when food will spoil, which may lead to food waste or poisoning. Therefore, they decided to create a new packaging that can respond to changes in food to better indicate when the food deteriorates. They made four types of film similar to plastic packaging, each consisting of two layers, one of which is made of protein extracted from silk; The other layer is made of a covalent organic framework (COF). COF contains carbon and hydrogen, as well as other atoms such as oxygen or nitrogen, all arranged in a uniform grid with sufficient space between them, resulting in the formation of many pores in the material. The researchers examined these four types of films and confirmed that they are flexible enough to be used as packaging and non-toxic. Subsequently, they tested whether these films could be biodegradable. The results showed that after 30 days of standing in soil, 50% of the film with the best performance degraded, which is equivalent to existing biodegradable plastics. The COF layer exchanges protons and electrons with the liquid, so the new material will change color when immersed in solutions with different pH values. Due to the fact that the pH value of food increases with spoilage, researchers used a thin film as an intelligent color changing label and attached it to a package of raw chicken. At the beginning, the label was orange. After standing at 30 ℃ for 20 hours, the color of the label turned 17% lighter, indicating that the meat had started to spoil. (Outlook New Era Network)