Carbon nanotube sensors for exhaled breath components

Abstract

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 O2 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.