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The creation of highly sensitive optical CO2 sensors in air is an urgent problem, as it allows monitoring of the content of CO2 both indoors and in ambient air, where its level is usually 600...1000 ppm. As a sensitive element of the CO2 sensor, it is proposed to use a liquid crystal substance (cholesteric-nematic mixture based on 5CB with cholesteric impurities), supplemented with multi-layered carbon nanotubes. The spectral characteristics of the liquid crystal mixture in the range of 400...600 nm were studied. The content of carbon nanotubes ranged from 0.1 to 0.5 wt.%. It was established that with an increase in concentration in the range of 10...100 mg/m3, the transmission minimum shifts to the long-wave region of the spectrum. The maximum spectral sensitivity in this range is 6 nm ⁄ mg ⁄ m3. The researched material can be used as a sensitive element of an optical CO2 sensor. Further research should be conducted in the direction of investigating the interaction of such a composite with other gases, as well as finding opportunities to improve the properties of the composite. Perhaps the use of multi-walled carbon nanotubes. [ABSTRACT FROM AUTHOR]