Biomedical Engineering Reference
In-Depth Information
of environmental pollutions although such odor is not restricted. All environmental
pollutants, regardless of their regulation, need to be monitored to improve quality
of life. For this purpose, the development of further effective methods to monitor
various pollutants is required.
GC-MS has been generally used for the detection of environmental pollutants in
the atmosphere [
79
-
81
]. HPLC is suitable to analyze the composition of water [
82
-
84
]. Such techniques can precisely quantify the amount of chemical compounds.
Thus, they are effective to monitor restricted pollutants. However, they have disad-
vantages in terms of portability and immediacy. Because of the large-sized instru-
ment, an on-site measurement is difficult, and sampling processes should be con-
ducted. In addition, real-time measurements are difficult due to the complexity of
analysis processes. Furthermore, equipment such as GC and HPLC is too expensive
to be used for the broad and continuous detection of less severe pollutants, such as
the odor from rotten foods or smoking.
Electronic noses can be effectively and extensively applied to the monitoring
of such environmental pollutants. Many electronic noses have been developed for
various purposes, such as the monitoring of urban pollution, water pollution, and
the quality of indoor air [
85
-
89
]. Severe environmental pollutants are mainly toxic
gases which are major targets of the electronic noses; thus, electronic noses are ap-
propriate for the monitoring of pollutants. In addition, the sensing processes can be
simplified. This is very important to detect hazardous chemicals such as CO, HF,
and NO
2
. However, the sensitivity of electronic noses is insufficient. The sensor
should detect toxic gases before the amount of toxins reaches a dangerous level, and
can also selectively recognize the existence of pollutants under any circumstances.
However, electronic noses are easily affected by a variety of factors, such as humid-
ity, electromagnetic fields, and temperature.
Bioelectronic noses are being regarded as a better sensor system to monitor a
number of environmental pollutants in terms of high sensitivity and selectivity.
There is, however, a potential complication as to whether a given biological ele-
ment is active under dry conditions, because the sensors should be able to detect gas
compounds. Wu and Lo addressed this problem by using a synthetic peptide which
mimics the binding site of olfactory receptors [
90
,
91
]. The sensor functionalized
with peptide receptors was able to selectively detect trimethylamine and ammonia,
which are well known as air pollutants due to their pungent odor. Lee et al. demon-
strated that whole olfactory receptor proteins were active in the dry condition [
78
].
They functionalized a conducting polymer nanotube-based sensor with a human
olfactory receptor which had been expressed in
E. coli
. This sensor not only detect-
ed specific odorants with high sensitivity and selectivity, but also showed human
nose-like behaviors such as antagonism. In order to make a better tertiary structure
of olfactory receptors, the whole proteins were trapped in a 'nanodisc', a self-as-
sembling nano-scale membrane assembly [
6
]. The nanodiscs containing olfactory
receptors were utilized for the functionalization of carbon nanotubes, and the sensor
successfully detected gaseous odorants. All things taken together, the bioelectronic
nose can fully supplement the weakness of the electronic nose, and will be widely
used for the monitoring of a range of environmental pollutants.
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