High sensitivity, moisture selective, ammonia gas sensors based on single-walled carbon nanotubes functionalized with indium tin oxide nanoparticles

An effective monitoring of the air quality in an urban environment requires the capability to measure polluting gas concentrations in the low-ppb range, a limit so far virtually neglected in most of the novel carbon nanotube (CNT)-based sensors, as they are usually tested against pollutant concentrations in the ppm range. We present low-cost gas sensors based on single-walled CNT (SWCNT) layers prepared on plastic substrates and operating at room temperature, displaying a high sensitivity to [NH3]. Once combined with the low noise, the high sensitivity allowed us to reach an ammonia detection limit of 13 ppb. This matches the requirements for ammonia monitoring in the environment, disclosing the possibility to access the ppt detection limit. Furthermore, a blend of SWCNT bundle layers with indium-tin oxide (ITO) nanoparticles resulted in a threefold sensitivity increase with respect to pristine CNT for concentrations above 200 ppb. Finally, the peculiar response of the ITO-SWCNT blend to water vapor provides a way to tailor the sensor selectivity with respect to the relevant interfering effects of humidity expected in outdoor environmental monitoring