How do you know if a medicine that must be kept refrigerated, like many vaccines, has been kept at the right temperature? These new materials indicate
Some foods and medicines, like many COVID-19 vaccines, must be kept refrigerated. In search of a robust and stable technique for use when products exceed safe conditions, a group of researchers from ACS Nano, part of the Shenzhen Institutes of Advanced Technology and the Shenzhen Fundamental Research Program, China, discovered a class of bright colors microcrystals in materials that become colorless over a wide range of temperatures and response times. To demonstrate the validity of the concept, the team of Chinese researchers placed the color-changing materials on the cap of a tube with a QR code.
Refrigerated chambers and refrigerated trucks usually maintain defined temperatures, but accidents can happen. It is possible to control the temperature of each product with wireless sensors, but these devices generate a lot of electronic waste. Recently, researchers have proposed the use of materials that work as visual indicators to provide this information without generating so much waste. However, some of the current options that use color reactions or dyes produce hues that may fade. In other cases, they can only detect temperatures above freezing, which isn’t helpful for some COVID-19 vaccines that can start to break down below freezing (above -4 or -94 degrees Fahrenheit). So Yadong Yin, Xuemin Du and their colleagues set out to develop a material with better color change and a modifiable melting point that would allow it to record a wide range of temperatures.
The researchers used structural colors instead of dyes for their indicator system. The team produced glycerol-coated silicon dioxide nanoparticles, which appeared bright green or red when they clump together to form microcrystals in water. Then they created liquids with different melting points by mixing different proportions of polyethylene glycol or ethylene glycol and water. When these two parts come into contact, the color disappears irreversibly as the temperature-sensitive solution dissolves and the microcrystals fall apart. Materials can be modified to record exposures to temperatures between -94 and +99 degrees Fahrenheit (-70 and 37 degrees Celsius), lasting from a few minutes to several days. In other experiments, two-part indicator systems were included in flexible round tube labels with a QR code. These systems are very sensitive and effectively detect when materials are at too high a temperature. The researchers say the color-changing materials could be useful for a variety of situations from cold chains to medical supplies.
REFERENCE
Self-destructing structural colored liquids for time and temperature indication