Carbon nanotube sensors for exhaled breath components

A new method for the detection of nitric oxide ( NO) in gas phase is based on a combination of acidic gas scrubbing, oxidation, and conductivity measurements using a chemically functionalized carbon nanotube field- effect transistor ( NTFET) device. Gas mixtures containing NO are passed through an Ascarite scrubber and then an oxidizing material ( CrO3) which converts NO into NO2. The latter is delivered to the surface of the NTFET sensor coated with poly( ethylene imine) ( PEI) polymer. Interaction of the gas with a chemically functionalized NTFET results in a conductivity change that is proportional to the NO gas concentration. The wide range of NO gas concentrations from about 2 ppb up to 5 ppm was tested. A detection limit of NO has been measured as 5 ppb with a signal- to- noise ratio ( S/ N = 3) in inert atmosphere at a fixed relative humidity ( RH = 30%). Cross- sensitivity to CO2 and O-2 was measured in the gas mixture, modeling human breath conditions. Compared to using chemiluminescence, a state- of- the- art technique for monitoring NO concentrations, this method offers the advantages of low cost, compact size and simplicity of set- up for monitoring NO concentrations while overcoming the limitations of cross- contaminants, possibly creating a foundation for enabling self- diagnostics and home care for asthma sufferers.