Citation: Hannon, A.; Seames, W.; Li,
J. Hybrid Carbon Nanotubes/Gold
Nanoparticles Composites for Trace
Nitric Oxide Detection over a Wide
Range of Humidity. Sensors 2022, 22,
7581. https://doi.org/10.3390/
s22197581
Academic Editor: Theodore E.
Matikas
Received: 26 August 2022
Accepted: 28 September 2022
Published: 6 October 2022
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Article
Hybrid Carbon Nanotubes/Gold Nanoparticles Composites for
Trace Nitric Oxide Detection over a Wide Range of Humidity
Ami Hannon
1,2
, Wayne Seames
2
and Jing Li
3,
*
1
KBR Wyle Inc. at NASA Ames Research Center, Moffett Field, CA 94035, USA
2
Department of Chemical Engineering, University of North Dakota, Grand Forks, ND 58201, USA
3
NASA Ames Research Center, Moffett Field, CA 94035, USA
* Correspondence: jing.li-1@nasa.gov; Tel.: +1-650-604-4352
Abstract:
Composites of functionalized single walled carbon nanotubes (SWCNTs) and gold nanopar-
ticles (Au NPs) of
≈
15 nm diameter were drop-cast on a printed circuit board (PCB) substrate
equipped with interdigitated electrodes to make a hybrid thin film. Addition of Au NPs decorated
the surface of SWCNTs networked films and acted as catalysts which resulted into an enhanced
sensitivity and low ppb concentration detection limit. The compositions of the film were character-
ized by scanning electron microscope (SEM). SWCNTs clusters were loaded with various amount
of Au NPs ranging from 1–10% (by weight) and their effect on Nitric oxide (NO) sensitivity was
studied and optimized. Further, the optimized composite films were tested in both air and nitrogen
environments and as well as over a wide relative humidity range (0–97%). Sensors were also tested
for the selectivity by exposing to various gases such as nitrous oxide, ammonia, carbon monoxide,
sulfur dioxide and acetone. Sensitivity to NO was found much higher than the other tested gases.
The advantage of this sensor is that it is sensitive to NO at low ppb level (10 ppb) with estimated
response time within 10 s and recovery time around 1 min, and has excellent reproducibility from
sensor to sensor and works within the wide range of relative humidity (0–97%).
Keywords:
chemiresistive sensor; carbon nanotubes; nitric oxide sensor; gold nanoparticles and
carbon nanotubes; ppb concentration detection; NOx sensor
1. Introduction
Nitric oxide detection has a wide application from environmental monitoring, indus-
trial process control, combustion studies, oceanographic study to medical diagnoses [
1
–
4
].
While it is possible today to measure trace gases such as NO, Nitrous oxide (N
2
O),
and Dimethyl sulfide (DMS) in the atmosphere, the sensors to measure dissolved gases in
seawater real time and in situ are limited to Carbon dioxide (CO
2
), Methane (CH
4
), and
hydrogen sulfide (H
2
S) [
5
]. Measurement of climatically relevant trace gases are necessary
to quantify ocean sources and sinks, and to understand their impact on global climate
change. Several of these climatically relevant gases are known to be produced under low
oxygen conditions, such as the oxygen minimum zones in the open ocean, and ‘dead zones’
in the coastal ocean. Global warming is the working hypothesis for the observed expansion
of open ocean Oxygen Minimum Zones (OMZs); increased stratification reduces upper
ocean ventilation and Aeration [
6
–
8
]. Expansion of hypoxia in the coastal zone is linked
to eutrophication associated with excess nutrients in river runoff, from sources such as
chemical fertilizers applied to farms, fields, and lawns [
9
]. Marine life becomes highly
stressed under hypoxic conditions, and dramatic ecological impacts can occur, including
massive kills of fish and shellfish and harmful algae blooms. Longer lasting impacts
also occur since juvenile fish are more likely to be affected than mature fish, resulting
in detrimental follow-on effects such as economic losses. For Texas, with a doubling
in population predicted by 2050, the impact of hypoxia on the coastline’s ecosystem and
Sensors 2022, 22, 7581. https://doi.org/10.3390/s22197581 https://www.mdpi.com/journal/sensors
