by growing ZnO nanorods on SnO 2 nanowires backbone. This hierarchical
nanosensors displayed enhanced and selective response for ethanol, as compared
to bare SnO 2 nanowires sensor.
Nanosensors have also been effectively used for the detection of carcinogenic
(cancer causing) gases from air. One of the major human carcinogens is benzene.
Wang et al., fabricated a highly sensitive, and rapid gas sensor for benzene and
toluene, using Au NPs modified ZnO nanowires (Au-ZnO NWs) (Wang et al. 2013).
Chlorinated aliphatic hydrocarbons are also carcinogenic in nature and these
chemicals also result in numerous other serious health issues. These chemicals
include dichloromethane (CH 2 Cl 2 ), chloroform (CHCl 3 ), carbon tetrachloride
(CCl 4 ), etc., Kar and Choudhury (2013) reported nanocomposites developed with
PANI doped with carboxylic acid functionalized MWCNTs (PANI/c-MWCNTs) for
detection of chloroform. PANI/c-MWCNTs showed better response from chloroform as compared to pure PANI, due to better interactions of modified PANI
backbone with chloroform.
Besides organic gases, inorganic gases like ammonia (NH 3 ), the oxides of
sulphur (SO X ) and nitrogen (NO X ) also act as toxic air pollutants. Sulphur dioxide
(SO 2 ) is released into the environment as a result of activities like combustion of
petroleum or coal with sulphur content and volcanic eruptions. In the presence of
catalysts like NO 2 , SO 2 released in the atmosphere is also prone to H 2 SO 4 acid
formation, causing acid rain. For the detection of SO 2 , Tyagi et al. (2017) developed
an efficient gas sensor by integrating SnO 2 thin film with NiO dotted cluster (10 nm
thin). The sensor displayed much better response for SO 2 as compared to bare SnO 2
thin film. Hydrogen sulphide (H 2 S) is also a gaseous pollutant, which can affect the
human nervous system, and is released into the environment during fuel production
or biological processes. In their work, Su and Peng (2014) developed PPy/WO 3
nanocomposite film based gas nanosensors for H 2 S detection at room temperature.
The sensor displayed long-term stability (~54 days), higher response than pure PPy
or WO 3 films, and long linear working range (100–1000 ppb).
Cui et al. (2018) recently developed a highly selective, sensitive, portable and
flexible self-powered NH 3 nanosensor. Triboelectric nanogenerators (TENG) based
on polyaniline nanofibers (PANI NFs) were used for developing the nanosensor. The
gas sensor was integrated with the power supply to form a single device. The sensing
principle involves change in the electroconductivity of PANI after NH 3 exposure
resulting in reduction in the output voltage of TENG. The sensor exhibited a LOD of
500 ppm at room temperature.
Nitrogen dioxide (NO 2 ) is another harmful gas released mainly from vehicular
emissions and from chemical industries due to combustion at high temperatures.
NO 2 also involves in atmospheric reactions, leading to the formation of ozone (O 3 ) at
ground level. Navale et al. developed camphor sulphonic acid (CSA) doped
PPy/α-Fe 2 O 3 hybrid nanocomposite, and used these hybrid nanocomposites as room
temperature gas sensor (Navale et al. 2014). The nanosensors exhibited highly
selectivity for NO 2 in the presence of other reducing and oxidizing gases with low
LOD of 5 ppm.
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U. Chakraborty et al.
nanosensors displayed enhanced and selective response for ethanol, as compared
to bare SnO 2 nanowires sensor.
Nanosensors have also been effectively used for the detection of carcinogenic
(cancer causing) gases from air. One of the major human carcinogens is benzene.
Wang et al., fabricated a highly sensitive, and rapid gas sensor for benzene and
toluene, using Au NPs modified ZnO nanowires (Au-ZnO NWs) (Wang et al. 2013).
Chlorinated aliphatic hydrocarbons are also carcinogenic in nature and these
chemicals also result in numerous other serious health issues. These chemicals
include dichloromethane (CH 2 Cl 2 ), chloroform (CHCl 3 ), carbon tetrachloride
(CCl 4 ), etc., Kar and Choudhury (2013) reported nanocomposites developed with
PANI doped with carboxylic acid functionalized MWCNTs (PANI/c-MWCNTs) for
detection of chloroform. PANI/c-MWCNTs showed better response from chloroform as compared to pure PANI, due to better interactions of modified PANI
backbone with chloroform.
Besides organic gases, inorganic gases like ammonia (NH 3 ), the oxides of
sulphur (SO X ) and nitrogen (NO X ) also act as toxic air pollutants. Sulphur dioxide
(SO 2 ) is released into the environment as a result of activities like combustion of
petroleum or coal with sulphur content and volcanic eruptions. In the presence of
catalysts like NO 2 , SO 2 released in the atmosphere is also prone to H 2 SO 4 acid
formation, causing acid rain. For the detection of SO 2 , Tyagi et al. (2017) developed
an efficient gas sensor by integrating SnO 2 thin film with NiO dotted cluster (10 nm
thin). The sensor displayed much better response for SO 2 as compared to bare SnO 2
thin film. Hydrogen sulphide (H 2 S) is also a gaseous pollutant, which can affect the
human nervous system, and is released into the environment during fuel production
or biological processes. In their work, Su and Peng (2014) developed PPy/WO 3
nanocomposite film based gas nanosensors for H 2 S detection at room temperature.
The sensor displayed long-term stability (~54 days), higher response than pure PPy
or WO 3 films, and long linear working range (100–1000 ppb).
Cui et al. (2018) recently developed a highly selective, sensitive, portable and
flexible self-powered NH 3 nanosensor. Triboelectric nanogenerators (TENG) based
on polyaniline nanofibers (PANI NFs) were used for developing the nanosensor. The
gas sensor was integrated with the power supply to form a single device. The sensing
principle involves change in the electroconductivity of PANI after NH 3 exposure
resulting in reduction in the output voltage of TENG. The sensor exhibited a LOD of
500 ppm at room temperature.
Nitrogen dioxide (NO 2 ) is another harmful gas released mainly from vehicular
emissions and from chemical industries due to combustion at high temperatures.
NO 2 also involves in atmospheric reactions, leading to the formation of ozone (O 3 ) at
ground level. Navale et al. developed camphor sulphonic acid (CSA) doped
PPy/α-Fe 2 O 3 hybrid nanocomposite, and used these hybrid nanocomposites as room
temperature gas sensor (Navale et al. 2014). The nanosensors exhibited highly
selectivity for NO 2 in the presence of other reducing and oxidizing gases with low
LOD of 5 ppm.
120
U. Chakraborty et al.