“…Nevertheless, some people with asthma do not perceive their symptoms sufficiently well [ 14 , 15 ] and, thus, do not realize that their condition is deteriorating. By monitoring FeNO, patients can compare their daily symptoms with the monitoring results, and, subsequently, this can help them to manage and avoid the worsening of their asthma in a timely manner [ 16 ]. According to the type of conversion signal, common NO sensors can be categorized as either electrochemical or optical sensors [ 17 , 18 ].…”