Carbon dioxide (CO₂) is a major respiratory metabolite, and continuous monitoring of CO₂ concentration in exhaled breath is not only an important indicator for early detection and diagnosis of respiratory and circulatory system diseases, but can also be widely used for monitoring personal exercise status. KAIST researchers have succeeded in accurately measuring CO₂ concentration by attaching a sensor to the inside of a mask.

Existing non-invasive CO₂ sensors are limited by their large size and high power consumption. Optochemical CO₂ sensors using fluorescent molecules are able to be miniaturized and are lightweight, but due to the photodegradation phenomenon of dye molecules, they are difficult to use stably for a long time, which limits their use as wearable health care sensors.