Biomedical Engineering Reference
In-Depth Information
room temperature. The gas adsorption properties of the MPP-
functionalized CNTs exhibited broad selectivity and high sensitivity.
PCA analysis was performed using the gas response of a sensors
array by providing a capability of the compounds recognition. These
results were considered very promising for the development of
arrays of CNT-based gas nanosensors with broad selectivities for
fingerprinting analysis of gaseous complex samples.
Another class of functional materials based on metal oxides, e.g.,
nanocrystals of tin dioxide (SnO
), for CNTs miniaturized sensors
has been recently investigated [226, 252]. Existing SnO
2
sensors are
very sensitive and typically operate at temperatures over 200°C to
enhance the surface adsorption/reaction kinetics and sensitivity that
requires continuous heating of the sensor, considerable electrical
power consumption and increased sensor cost. The Rutile-structured
tin dioxide thin film sensors are
2
-type semiconducting materials
widely used in gas-sensing applications and commercial devices.
Their main drawbacks are cross-sensitivity, lack of selectivity, and
high temperature operations. An emerging strategy to overcome
these limitations is the use of SnO
n
nanocrystals as functional material
2
onto
-type CNTs networks for enhanced gas sensing. Under control
of thickness and size of the
p
n
-type SnO
nanocrystals, the electrical
2
properties of hybrid material SnO
/CNT can change from
p
-type to
2
n
-type due to charge transfer induced by gas adsorption. Figure 9.26
shows the device and sensing performance of the proposed sensor.
. [226] demonstrated the feasibility to fabricate a gas sensor
configured as SnO
Lu
et al
nanocrystals functionalizing the CNT networks
for improved gas detection of 25, 50, 100 ppm NO
2
, 100 ppm CO,
2
0.1% and 1% H
diluted in air, operating at room temperature. This
hybrid platform as a sensing element is potentially superior to either
of its constituent components.
2
. [252] demonstrated the promising
sensing properties of hybrid material based on sputtered SnO
Furthermore, Yang
et al
2
nanoparticles functionalizing the SWCNT networks for improved H
2
gas detection down to 100 ppm and working at room temperature.
The gas sensing behavior of SnO
-SWCNT network sensors was
2
changed from
p
-type to
n
-type with increasing SnO
deposition time,
2
i.e., increasing surface coverage of SnO
on SWCNT.
Special attention has been paid to the metal catalysts, especially
in the form of nanoclusters, as functional materials for advanced
CNT-based gas sensors. Metals exhibit a broad range of electronic,
chemical, and physical properties that are often highly sensitive
2
