Applications and Perspectives of Bioelectronic Nose - Bioelectronic Nose: Integration of Biotechnology and Nanotechnology - page 265

conditions of a person can affect the smelling ability; therefore, reproducibility and
repeatability cannot be guaranteed through this method. In the case of the fragrance-
and flavor-related industries, a vast number of odorous components are used. Also,
the actual smell may be extremely changeable depending on the mixing ratio of the
used odorants. Thus, it is impossible to determine scent through analytical tech-
niques such as GC-MS. Such techniques can only identify components comprising
the smell [ 74 , 75 ]. This is the most serious drawback of conventional techniques on
the applications for the fragrance and flavor industry.
Electronic noses can provide a more objective value of odor. Several groups
have reported results showing the capability of electronic noses on applications for
the measurement of scent [ 76 , 77 ]. Electronic noses have successfully discriminated
perfumery compounds through a pattern recognition process. However, the patterns
generated by the odor stimulation cannot fundamentally represent the real odor that
a person perceives, because electronic noses do not use human olfactory receptors.
The electronic nose detects volatile compounds including odorants. Thus, various
odorless compounds, such as CO 2 , CO, and even water vapor, can induce signifi-
cant responses in the electronic nose. Hence, in the fragrance and flavor industry
where the human perception has to be objectively analyzed, the electronic nose has
limitations.
Bioelectronic noses utilize olfactory receptors which originally act as a pri-
mary sensing element for the recognition of odors. The biological processes for
odor perception can be reconstructed in vitro using bioelectronic noses. Olfactory
receptors of the bioelectronic nose recognize odorants with excellent selectivity.
This recognition is identical to that of the human nose [ 78 ]. If the sensor is func-
tionalized with all kinds of human olfactory receptors, it can perfectly represent
the same response patterns as those which the human nose produces for the percep-
tion of odors. In order to apply the sensor to the fragrance and flavor industry, the
sensor should objectively analyze the type and intensity of the smell based on the
human olfactory sense. This is only possible when human olfactory receptors are
incorporated to the sensor system. Eventually, the bioelectronic nose will provide
a simple, fast and reliable analysis method to measure scent without the help of
the human nose.

14.1.4 Monitoring of Environmental Pollutants

Recently, there has been a growing need to more consistently and specifically moni-
tor environmental pollutants. In a narrow sense, environmental pollution means the
emission of greenhouse gases or toxic compounds generated from industrial pro-
cesses into the atmosphere, soil, or water. This is strictly regulated by law, because
pollutants can be seriously harmful to human health. In the broader sense, there are
a lot of pollutions that are not officially regulated, but can give rise to unpleasant
feelings by malodor. For instance, garbage thrown in the street, spoiled fish in the
wastebasket, or smoking in the public area can cause malodor. Thus, it is also a kind