Carbon dioxide is a major metabolic byproduct released during respiration, and continuously monitoring the carbon dioxide concentration in exhaled breath can facilitate the early detection and diagnosis of respiratory and circulatory diseases. Recently, domestic researchers successfully attached ultra-low-power carbon dioxide sensors inside masks to accurately measure carbon dioxide concentration in real time.
Professor Yoo Seung-hyeop and researchers from the Korea Advanced Institute of Science and Technology (KAIST) announced on the 10th that they have developed a low-power, high-speed wearable carbon dioxide sensor capable of stable real-time respiratory monitoring. This research was published online on the 22nd of last month in the journal "Device," which is a sister journal of the international academic journal "Cell."
Photochemical carbon dioxide sensors utilize the principle that the intensity of fluorescence emitted by fluorescent molecules decreases with the concentration of carbon dioxide. Although photochemical carbon dioxide sensors using fluorescent molecules can be miniaturized and made lightweight, long-term stable use has been difficult due to "photodegradation," which occurs when dye molecules are altered or damaged by light.
To solve this problem, the researchers developed an ultra-low-power carbon dioxide sensor consisting of a light-emitting diode (LED) and an organic photodiode surrounding it. A photodiode is a material that can convert light energy into electrical energy. This sensor can operate with much lower power at 171 μW (microwatts) compared to existing sensors that consume several mW (milliwatts), thus reducing energy consumption by several tens of times.
In addition, the researchers clarified the mechanism of photodegradation of the fluorescent molecules used in the carbon dioxide sensor. Based on this, they identified the cause of increasing errors in photochemical sensors as usage time increases and found an optical design method to reduce these errors, which was applied to the sensor.
The developed sensor is lightweight at 0.12 g and thin at 0.7 mm, allowing it to be attached inside a mask. The sensor can accurately measure carbon dioxide concentration and differentiate between inhalation and exhalation in real time, monitoring the breathing rate as well. Unlike previous sensors that could only operate for about 20 minutes, the newly developed sensor can be used for up to 9 hours, and it can be reused by simply replacing the fluorescent film.
Professor Yoo said, "The sensor developed this time has excellent characteristics such as low power consumption, high stability, and flexibility, allowing it to be widely applied to wearable devices," and noted that it can be used for the early diagnosis of various diseases, including hypercapnia, chronic obstructive pulmonary disease, and sleep apnea.
Reference materials
Device (2025), DOI: https://doi.org/10.1016/j.device.2024.100681