Hydrogen cyanide (HCN) featured with high volatility and high adsorption is a common toxic and hazardous gas. Traces of HCN are also found in human exhaled breath. Unusual high HCN concentration in the breath of cystic fibrosis (CF) patients is associated with Pseudomonas aeruginosa (PA) infection. Therefore, the development of a highly sensitive online HCN measurement in exhaled breath can enable rapid screening for PA infection in CF patients.