Optical carbon dioxide sensors based on silicone-encapsulated room-temperature ionic liquids

Novel optical carbon dioxide sensors are based on emulsion of room-temperature ionic liquids (RTILs)-1-butyl-3-methylimidazolium salts in a silicone rnatrix. Semiquantitative determination of CO2 is achieved by dissolving an absorption-based pH indicator (thymol blue, TB, or bromthymol blue, BTB) in the RTIL. A quantitative fluorimetric sensor makes use of 8-hydroxypyrene-1,3,6-trisulfonate (HPTS). The response of the fluorimetric sensors to CO2 can easily be linearized which makes (re)calibration of the sensor very simple. It is demonstrated that a reference inert fluorescent dye (4-dicyanomethylene-2-methyl-6-(4-(dimethylamino)styryl)-4H-pyrane) can be added for ratiometric measurements. It is also shown that stable inorganic salts such as sodium phosphate can be used instead of quaternary ammonium hydroxides. Sensitivity of the material can be tuned by varying the pK(a) of an indicator. The sensors can find application in biotechnology, environmental monitoring, and food-packaging technology.