Humidity-Independent Oxide Semiconductor Chemiresistors Using Terbium-Doped SnO2 Yolk–Shell Spheres for Real-Time Breath Analysis

The chemiresistive sensing characteristics of metal oxide gas sensors depend closely on ambient humidity. Herein, we report that gas sensors using Tb-doped SnO2 yolk-shell spheres can be used for reliable acetone detection, regardless of the variations in humidity. Pure SnO2 and Tb-doped SnO2 yolk-shell spheres were prepared via ultrasonic spray pyrolysis and their chemiresistive sensing characteristics were studied. The sensor resistance and gas response of the pure SnO2 yolk-shell spheres significantly changed and deteriorated upon exposure to moisture. In stark contrast, the Tb-doped SnO2 yolk-shell spheres exhibited similar gas responses and sensor resistances in both dry and humid [relative humidity (RH) 80%] atmospheres. In addition, the Tb-doped SnO2 yolk-shell sensors showed a high gas response (resistance ratio) of 1.21 to the sub-ppm-levels (50 ppb) of acetone with low responses to the other interference gases. The effects of Tb oxide and the chemical interactions among the Tb oxide, SnO2, and water vapor on this humidity-independent gas sensing behavior of the Tb-doped SnO2 yolk-shell sensors were investigated. This strategy can provide a new road to achieve highly sensitive, selective, and humidity-independent sensing of acetone, which will facilitate miniaturized and real-time exhaled breath analysis for diagnosing diabetes.