In Situ Synthesis of Ordered Macroporous Metal Oxides Monolayer on MEMS Chips: Toward Gas Sensor Arrays for Artificial Olfactory.

Metal oxide semiconductor gas sensors have attracted particular attention due to their merits of high sensitivity and easy integration. However, their insufficient selectivity severely limited their applications, especially in identifying low-concentration gases in a complex environment. Herein, inspired by the human olfaction, an in situ colloidal assembly strategy is developed to directly synthesize ordered macroporous metal oxide monolayers on micro-electromechanical system (MEMS) chips. It enables wafer-scale fabrication of gas sensors with excellent device-to-device consistency, which is beneficial for the construction of a highly reliable artificial olfactory system. In order to exploit efficient sensor arrays, five different monolayer macroporous gas sensitive materials with high specific surface areas, diverse nanostructures, rich catalytically active sites, and diverse compositions are synthesized in situ on MEMS chips, which displayed tailored selectivity and sensing behaviors. The crucial cross-selectivity contributes to the complex gas identification. Based on principal component analysis and back propagation neural network algorithm, an advanced artificial olfactory system is constructed, which can distinguish four different common hazardous gases with accurate concentrations, including hydrogen sulfide, carbon monoxide, acetone, and toluene. The proposed MEMS-based artificial olfactory system holds great promise to develop an electronic nose for detection of toxic gases in a complex environment.