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.