Inflammable breath gases such as H₂ and CH₄ are used as bio markers for monitoring the condition of the colon. However, their typical concentrations of below 100 ppm pose sensitivity and selectivity challenges to current gas sensing systems without the use of chromatography. We fabricated a compact, gas-selective thermoelectric array sensor (TAS) that uses micro-machined sensor devices with three different combustion catalysts to detect gases such as H₂, CO, and CH₄ in breath. Using Pt/Pt-W thin-film micro-heater meanders, Pd/Al₂O₃, Pt,Pd,Au/Co₃O₄, and Pt/Al₂O₃ catalysts were heated to 320, 200, and 125 °C, respectively, and the gas sensing performances of the TAS for each gas and for a model breath gas mixture of 100 ppm H₂, 25 ppm CO, 50 ppm CH₄, and 199 ppm CO₂ in air were investigated. Owing to its high catalyst temperature, the Pd/Al₂O₃ catalyst burned all three gases, while the Pt,Pd,Au/Co₃O₄ burned CO and H₂ and the Pt/Al₂O₃ burned H₂ selectively. To calibrate the gas concentration of the mixture gas without the use of a gas separation tool, linear discriminant analysis was applied to measure the sensing performance of TAS. To enhance the gas selectivity against H₂, a double catalyst structure was integrated into the TAS sensor.
Keywords: CH4; CO; H2; array sensor; combustion catalyst; micro-electromechanical systems (MEMS); thermoelectric device.