36 Nanosensors: Physical, Chemical, and Biological
smelling and breathing. Similarly many other organs serve multiple func-
tions. Multifunctionality is also expected from nanosensors.
1.13.5 Sensitivity Considerations and Need of Functionalization
Many sensors are based upon the adsorption of target analytes and adsorp-
tion depends on surface area and surface chemistry. Making a sensor out
of a nanoporous or nanocrystalline material increases the surface area tre-
mendously, for example, the surface area of a single-walled carbon nanotube
(SWCNT) is 1600 m
2
g
−1
. Sensitivity of a gas sensor is augmented several-
fold by increasing the surface area. By using tin oxide (SnO
2
), indium oxide
(In
2
O
3
), antimony oxide (Sb
2
O
3
) or zinc oxide (ZnO) in ...