Biomedical Engineering Reference
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gating. Polymer modification was used to impart high sensitivity and
selectivity to the sensors toward ammonia and nitrogen dioxide. PEI
coating affords
n
-type nanotube devices capable of detecting NO
at
2
less than 1 ppb concentrations, while being insensitive to NH
. In the
3
contrast, Nafion blocks NO
.
Detection of molecules in a gas mixture was demonstrated by using
the multiplexed nanotube sensors.
and allows for selective sensing of NH
2
3
(a)
(b)
Figure 9.17
(a) Optical image showing three CNT devices after
microspotting with droplets of polymer CNT solutions.
(b) Red (top) curve: a device coated with Nafion exhibits
response toward 100 and 500 ppm of NH
in air, and no
3
response when 1 ppm of NO
was introduced to the testing
environment. Blue (bottom) curve: in the contrast, a PEI-
coated device exhibiting no response toward 100 and
500 ppm of NH
2
and a large conductance decrease toward
3
1 ppm of NO
. This figure is reprinted and adapted with
permission from ACS [175]. See also Color Insert.
2
A more and more attention has been paid to the
composite
materials
for gas sensing applications due to their possibility to
operate at room temperature with high performance. Compared to
counterpart metal oxides sensors, the CNT-based nanocomposites
work at room temperature and are easy to fabricate. Polymer
composite materials consist of a polymeric matrix which acts
as an insulating matrix and dispersed particles, e.g., nanotubes,
of conducting materials which act as conducting path of the
nanocomposite materials. The gas sensing behavior of conducting
filler-matrix composite materials can be described by the volumetric
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