Low-Powered MEMS Sensor-Array System for Detection of H2/CH4 for the Potential Application of SIBO Diagnosis

The detection of hydrogen-methane (H2-CH4) in exhaled breath takes on paramount importance for small intestinal bacterial overgrowth (SIBO) diagnosis. However, the concentrations of H2 and CH4 associated with SIBO are significantly lower, reaching only 20 and 12 ppm, respectively. Furthermore, the detection of these gases can be compromised by the presence of various volatile organic compounds (VOCs) and relative humidity (RH) in exhaled breath. In this study, a low-powered system with three high-performance tin dioxide (SnO2)-based micro-electro-mechanical system (MEMS) gas sensors for H2-CH4-VOCs detection was modified by magnetron sputtering deposition and coating, which are named as Pd/SnO2-M (M means magnetron), Pd/SnO2-C (C means coating), and SnO2-D (D means multiple doping), respectively. Particularly, the Pd/SnO2-M sensor shows excellent selectivity, high sensitivity, and low detection limitation (down to 0.033 ppm) toward H2, which is attributed to the compact grains of the film and the Pd catalysis for the dissociation of H2 molecule into two active hydrogen atoms better than other gases. In addition, the Pd/SnO2-C sensor exhibits high sensitivity and low detection limitation toward H2 (down to 0.186 ppm) and CH4 (down to 1.1 ppm) since doped Pd also gives rise to adsorbed oxygen species (Oads) above the SnO2 surface besides its catalysis. Moreover, the assembled MEMS sensor array system demonstrates gas recognition capability based on linear discriminant analysis (LDA) under controlled single-gas conditions in high-humidity environments. Then, the as-modified MEMS sensor array system is a promising platform for H2-CH4 detection.