Appearing green on a vial lid (left), this structural color material becomes colorless (right) when warmed. Credit: Adapted from ACS Nano 2023, DOI: 10.1021/acsnano.3c00467
Key points:
- Researchers developed nanoparticle-based indicators that change colors when medications get too warm.
- The two-part indicators proved to be very sensitive in proof-of-concept experiments.
- They could be vital to the future cold chain supply.
As the world learned during the first iterations of the COVID-19 vaccine, some medications need to be kept at a specific temperature. If not, they lose their efficacy, and can even be dangerous when “expired.”
But how do you tell if a medication has been kept at its optimal temperature? Researchers at the Chinese Academy of Sciences have made it easier with color-changing materials.
For their research published in ACS Nano, the scientists developed a class of brilliantly colored microcrystals in materials that become colorless over a wide range of temperatures and response times. As a proof of concept, the team packaged the color-changing materials into a vial lid and QR code.
The researchers used structural colors, instead of dyes, for their indicator system. They made glycerol-coated silicon dioxide nanoparticles, which appeared bright green or red when clustered together into microcrystals in water. Next, the scientists created liquids with variable melting points by mixing different proportions of polyethylene glycol or ethylene glycol and water. When these two parts were put together, they could produce an irreversible color loss when the temperature-triggered solution melted and the microcrystals broke apart. The materials can be customized to track temperature exposures from -94 to +99 F that lasted from a few minutes to multiple days.
In other experiments, the two-part indicator systems were packaged into flexible round vial labels and a QR code. These systems were very sensitive and successfully indicated when the materials got too warm.
The researchers say structural color-changing materials hold promise for diverse scenarios encountered in cold supply chains.