Humidity-activated ammonia sensor with excellent selectivity for exhaled breath analysis

Abstract High ammonia (NH3) concentration in the exhaled breath can be used as a crucial biomarker for end-stage of renal disease. Detecting exhaled ammonia via gas sensors remains a huge challenge, because of the complex components and high humidity environment of exhaled gases. Herein, a creative design for NH3 sensing is realized using a humidity-activated mechanism at room temperature. The investigation reveals that the carboxylate formation reaction specific recognition of NH3 can be activated under high humid environment. An environmentally friendly and non-toxic biomass hydrogel NH3 sensor was developed, with poly- l -aspartic acid (PAA) and l -glutamic acid (GA) as the sensing material. The response to 50 ppm NH3 can reach 9.2 under 80 % RH at room temperature. The humidity-activated sensing mechanism is proposed as a complex process involving the acid-base adsorption, the formation of ionic conduction and the reaction between carboxylic acid groups and NH3. It is believed that the PAA/GA sensor presents a new pathway for highly selective detection of NH3 under high humidity condition, which is a promising method for analyzing the exhaled ammonia.