Nitrous Oxide Sensor Detects Imminent Asthma Attacks

An innovative gas sensor identifies when an asthma sufferer's air passages are about to become inflamed, enabling the patient to take preventive anti-inflammatory medication.

The nitrous monoxide (NO) sensor is contained in a complementary metal oxide semiconductor (CMOS) chip on a platform, which upon exposure to hydrogen detects changes in the work function of a palladium component that serves as the gate contact of a metal oxide semiconductor field-effect transistor (MOSFET). The detection process involves initial conversion of NO into nitrogen dioxide, after which the air flows across the actual sensor. The nitrogen dioxide particles signaling the attack adhere to the sensor's surface, which generates a voltage that is measured by a field-effect transistor; the intensity of the voltage is directly dependent on the amount of NO in the patient's breath. Based on this value, the patient can decide what dose of anti-inflammatory medication he or she should take.


The sensor is able to detect increases in NO one day before an acute asthma attack occurs, and is so sensitive it can detect amounts as small as one part per billion (PPB), making it as sensitive as larger devices that are far more expensive and not portable at all. A similar type of breath sensor under consideration would allow athletes to check whether they are exercising enough to burn fat by measuring the level of acetone, which is generated in the body when fat is burned and is also detectable in a person's breath. The new NO sensor is under development by Siemens (Munich, Germany;).

"Similar sensors to this are currently available in doctors' offices, but they are too bulky and expensive for individual use,” said Dr Maximilian Fleischer, who helped develop the device. "We use the universal CMOS chip platform. Different receptor layers can be attached to the platform to adapt it for different applications, such as the detection of fires.”

In patients suffering from asthma, the latent inflammation of the bronchial tubes generally spreads long before the patients actually feel anything. If the inflammation is intense, the air passages constrict and the patient has an asthma attack. The attacks can be so serious that the patient has to be treated in hospital, which is why many asthma sufferers regularly take anti-inflammatory medication. Previously, the only way to detect impending asthma attacks in advance was to conduct expensive pulmonary examinations to determine if the patient's breath contained heightened levels of NO.

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