Prajapati et al. (2020) reported ultralow-power nanosensor array platform by
using four nanosensors, integrated with four nanoheaters (4 μM Â 100 nm). ZnO,
1% Ag doped BaTiO 3 -CuO, WO 3 and V 2 O 5 were used as sensing materials for the
detection of CO, CO 2 , NO 2 and SO 2 , respectively. The nanosensor displayed
simultaneous detection of SO 2 (~94% for 3 ppm; 265
C), CO (~93.2% for
3 ppm; 300
C), NO 2 (~23.01% for 3 ppm; 150
C) and CO 2 (~76.3% for
1000 ppm; 265
C).
As mentioned in earlier sections, CNTs are robust with inert nature and display
excellent electrical properties, making them appropriate materials for FET-based
nanosensors. Many greenhouse gases and contaminating gases like NH 3 and NO 2
can be efficiently detected by gas sensors based on CNTs-FET. Kong et al. (2000)
displayed the enhancement or reduction of the electrical resistance of single-walled
carbon nanotubes (SWCNTs) upon exposure to electron donating (e.g., NH 3 ) or
electron withdrawing (eg., NO 2 ) gaseous molecules, thus making CNTs applicable
for electrochemical gas sensing operations. They also noted that as compared to
solid-state sensors, CNT sensors exhibited higher sensitivity and rapid response at
room temperature. By heating the CNT sensors to high temperature or by recovering
under ambient conditions, the CNT sensors also displayed reversible behaviour.
Change in resistance of SWNTs under the presence of O 2 was reported by Collins
et al. (2000) thus, making them suitable for the applications of gas sensing. Zahab
et al. reported change in SWCNT conductivity to n-type from p-type upon exposure
of H 2 O (water vapours) in surrounding atmosphere (Zahab et al. 2000). Varghese
et al. (2001) demonstrated qualitative detection of CO 2 , CO and NH 3 using
CNT-FET electrochemical nanosensors with two geometries. One with resistive
geometry having multi-walled carbon nanotube (MWCNTs) grown on SiO 2 with
serpentine pattern, and the other one with capacitative geometry, with a planar
interdigital capacitor decorated with MWNTS-SiO 2 composite.
5.3.3.2 Detection of Soil Samples
Soil is an important environmental resource and, soil quality assessment and monitoring is extremely necessary because all the living beings are dependent on soil for
food, habitat, fibres, recreation, even for waste and bi-products assimilation
(Arrouays et al. 2012). The quality of soil has direct effect on human food safety,
health, social development and sustainable growth of economy (Liu et al. 2013).
Major soil contaminants are released by urban and industrial solid wastes and
atmospheric depositions, metal smelting and mining, agricultural activities and
sewage irrigation (Lu et al. 2019). Such activities directly or indirectly release
dangerous soil contaminants like heavy metals and plastics, asbestos, herbicides,
fungicides, pesticides, and polyaromatic hydrocarbons (PAHs) into the soil. Hence,
regular surveys for soil monitoring and detection of these contaminants are essential
for maintaining the soil quality. Conventional analytical methods for soil monitoring
include, XRF, AAS, ICP-AES, etc., but more time consumption, high cost, need of
expert handling and lack of portability, make the use of these techniques less
convenient. These disadvantages can be tackled by using suitably designed
nanosensors, which are emerging as useful analytical tools for soil monitoring
5 Development of Environmental Nanosensors for Detection Monitoring. . .
121
using four nanosensors, integrated with four nanoheaters (4 μM Â 100 nm). ZnO,
1% Ag doped BaTiO 3 -CuO, WO 3 and V 2 O 5 were used as sensing materials for the
detection of CO, CO 2 , NO 2 and SO 2 , respectively. The nanosensor displayed
simultaneous detection of SO 2 (~94% for 3 ppm; 265
C), CO (~93.2% for
3 ppm; 300
C), NO 2 (~23.01% for 3 ppm; 150
C) and CO 2 (~76.3% for
1000 ppm; 265
C).
As mentioned in earlier sections, CNTs are robust with inert nature and display
excellent electrical properties, making them appropriate materials for FET-based
nanosensors. Many greenhouse gases and contaminating gases like NH 3 and NO 2
can be efficiently detected by gas sensors based on CNTs-FET. Kong et al. (2000)
displayed the enhancement or reduction of the electrical resistance of single-walled
carbon nanotubes (SWCNTs) upon exposure to electron donating (e.g., NH 3 ) or
electron withdrawing (eg., NO 2 ) gaseous molecules, thus making CNTs applicable
for electrochemical gas sensing operations. They also noted that as compared to
solid-state sensors, CNT sensors exhibited higher sensitivity and rapid response at
room temperature. By heating the CNT sensors to high temperature or by recovering
under ambient conditions, the CNT sensors also displayed reversible behaviour.
Change in resistance of SWNTs under the presence of O 2 was reported by Collins
et al. (2000) thus, making them suitable for the applications of gas sensing. Zahab
et al. reported change in SWCNT conductivity to n-type from p-type upon exposure
of H 2 O (water vapours) in surrounding atmosphere (Zahab et al. 2000). Varghese
et al. (2001) demonstrated qualitative detection of CO 2 , CO and NH 3 using
CNT-FET electrochemical nanosensors with two geometries. One with resistive
geometry having multi-walled carbon nanotube (MWCNTs) grown on SiO 2 with
serpentine pattern, and the other one with capacitative geometry, with a planar
interdigital capacitor decorated with MWNTS-SiO 2 composite.
5.3.3.2 Detection of Soil Samples
Soil is an important environmental resource and, soil quality assessment and monitoring is extremely necessary because all the living beings are dependent on soil for
food, habitat, fibres, recreation, even for waste and bi-products assimilation
(Arrouays et al. 2012). The quality of soil has direct effect on human food safety,
health, social development and sustainable growth of economy (Liu et al. 2013).
Major soil contaminants are released by urban and industrial solid wastes and
atmospheric depositions, metal smelting and mining, agricultural activities and
sewage irrigation (Lu et al. 2019). Such activities directly or indirectly release
dangerous soil contaminants like heavy metals and plastics, asbestos, herbicides,
fungicides, pesticides, and polyaromatic hydrocarbons (PAHs) into the soil. Hence,
regular surveys for soil monitoring and detection of these contaminants are essential
for maintaining the soil quality. Conventional analytical methods for soil monitoring
include, XRF, AAS, ICP-AES, etc., but more time consumption, high cost, need of
expert handling and lack of portability, make the use of these techniques less
convenient. These disadvantages can be tackled by using suitably designed
nanosensors, which are emerging as useful analytical tools for soil monitoring
5 Development of Environmental Nanosensors for Detection Monitoring. . .
121