Fine‐Tunable CO₂ Colorimetric Sensors and CO₂ Level Indicator Meter with Horizontal Linear Gauge via Inter‐Chain Spacers

Fine‐tuning the sensing properties of carbon dioxide (CO 2 ) colorimetric sensors is a challenging task. In this study, a short synthetic route is developed for CO 2 ‐responsive nanoparticles with diverse sensitivity and detection range across a wide range of CO 2 concentrations. This involves the addition of oily liquids as inter‐chain spacers, which changes the diffusivity of CO 2 gas into the sensing matrices without other chemical modifications. R values and the limit of detection (LOD) are estimated from Euclidean distance (ED) curves, indicating a ten‐fold difference in sensitivity. Optical and physical analyses revealed that these results arise from intercalating inter‐chain spacers between polymeric chains and modifying the gas diffusivity. Furthermore, the sensitivity and detection range can be easily tuned by mixing two CO 2 ‐responsive nanoparticles having different inter‐chain spacers, allowing the fabrication of the sensors with subtle differences in sensitivity and detection range. Based on these results, a CO 2 level meter with a horizontal linear gauge that allows visible identification of the level of CO 2 over the entire range of CO 2 concentrations (from 0% to 100%) is developed. Consequently, the findings will be helpful in achieving a better understanding of gas information and finding an effective way to control the characteristics of colorimetric sensors.