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 (CO2) colorimetric sensors is a challenging task. In this study, a short synthetic route is developed for CO2-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 CO2-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.