Materials for capacitive carbon dioxide microsensors capable of operating at ambient temperatures

The responses of alkylamine functionalized organic bridged polysilsesquioxanes on chemicapacitive sensors to carbon dioxide (CO₂) are described operating at temperatures ranging from 15 to 50°C. These hybrid organic–inorganic network materials were synthesized by the sol–gel polymerization of a mixture of a matrix monomer and functional monomer at various ratios followed by aging and ink-jet deposition of the sol on each capacitive sensor. During exposure of the sensor to known concentrations of analyte, the material’s capacitance was measured. From these changes in capacitance, detection limits ranging from 40 to 100 ppm were calculated. Furthermore, a correlation was observed with increasing length of the alkyl chain in the amine monomer correlating with an increase in CO₂ sensitivity and a decrease in water sensitivity. These materials offer a new method for CO₂ detection for building control systems or other low-power applications using low operating temperatures.