Sensors, Vol. 18, Pages 1579: Thermoelectric Array Sensors with Selective Combustion Catalysts for Breath Gas Monitoring (Sensors)

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.