Colorimetric gas indicators based on dye-doped natural polymers for food freshness monitoring

In this study, we developed colorimetric gas indicators that respond to exposure to ammonia gas, which may occur due to food spoilage. We prepared bio-compatible and eco-friendly anthocyanin dye and cellulose acetate (CA) polymer to fabricate the gas indicators. The color of anthocyanin-doped CA films changed depending on the time of exposure to ammonia gas or the concentration of the gas, which can be quantitatively analyzed by measuring the light absorption spectrum of the indicators. As the color of the indicator changed from purple to blue when exposed to ammonia gas, the absorption peak wavelength red-shifted from 535 nm to 615 nm. By enclosing the colorimetric films in fresh food packaging, we could monitor food spoilage in real-time. Additionally, we fabricated gas indicators in the form of electrospun nanofibrous membranes, which are highly porous and suitable for immediate gas detection. The nanofibrous gas indicators clearly distinguished ammonia gas concentrations ranging from 150 to 10,000 ppm.