Sensing of Biomolecules - Bionanoelectronics: Bioinquiring and Bioinspired Devices - page 98

2.5 Nanoelectronic Noses and Various Disease Detection

Nanoelectronic noses are gas sensors arranged into an array and able to detect
an odor fingerprint, which is further identified by a signal processing unit. The
nanoelectronic noses have important applications in a very large area of applica-
tions encompassing food quality control, landmine detection, or health screening
( Strike et al. 1999 ; Arshak et al. 2004 ). The electronic noses were used before
many nanotechnologies have appeared and are based on metal oxides, conducting
polymers, surface acoustic devices, quartz microbalances, FETs, and many other
principles. Odorant molecules are small, hydrophobic, have a molecular mass of
about 350 Da and are a mixture of hundreds of chemical species. The detection
limit for an odorant molecule is few parts per trillion, and thousands of odors can
be detected. The nanomaterials have extended the nanoelectronic nose sensitivity,
due to their large surface-to-volume ratio and miniaturization possibility. A simple
schematic representation of a nanoelectronic nose is presented in Fig. 2.38 .
A typical structure of a gas sensor is presented in Fig. 2.39 . The gas molecules
are sensed by changes in time in the electrical resistance (or conductance) or by
the conductance dependence on variations of an electrical gate. Presently, CNTs
are the most used nanostructures for gas sensing applications ( Zhang et al. 2008 ).
When molecules able to extract electrons, such as NO 2 or O 2 , and molecules

odor
molecules

decision
unit

signal
processing

sensor array

Fig. 2.38 A nanoelectronic nose

interdigitated
electrodes

Fig. 2.39 The typical
configuration of the gas
sensor

sensing material

substrate