Biomedical Engineering Reference
In-Depth Information
14.1.2.1
Escherichia coli
E. coli
, which exists in the intestines of humans and animals, is a representative bacterium of the
genus
Escherichia
and is chosen as a model organism in the biological research. Recently,
E. coli
was used to prepare microbial biosensors. Rainina et al. [94] utilized cryoimmobilized recombi-
nant
E. coli
cells to develop a microbial biosensor for the direct detection of neurotoxins, which is
capable of hydrolyzing a wide spectrum of OP pesticides and chemical warfare agents. The bio-
logical transducer was provided through the enzymatic hydrolysis of OP neurotoxins catalyzed by
organophosphate hydrolase. In the reaction, protons are generated with P-O, P-F, P-S, or P-CN
bonds cleaved, and the number of released protons corresponds with the quantity of organophos-
phate hydrolyzed and is measured by using a pH glass electrode as the physical transducer. The
cryoimmobilized
E. coli
cells exhibited stable hydrolytic activity for over 2 months under storage in
50 mM potassium phosphate buffer at 4°C and, therefore, provide the potential for the development
of a stable biotransducer for detecting various OP neurotoxins.
Biran et al. [95] used a cadmium-responsive promoter from
E. coli
fused to a promoterless
lacZ
gene to construct a biosensor. This whole-cell biosensor could detect nanomolar concentrations of
cadmium in water and soil samples within minutes, and it can be used for continuous online and
in situ
monitoring.
14.1.2.2
Bacillus subtilis
B. subtilis
is a species of the genus
Bacillus
, belonging to aerobic bacteria, which can catalyze the bio-
chemical degradation of organic matter in wastewater and is used for the fabrication of BOD biosen-
sor. Jia et al. [96] developed a novel type of BOD biosensor for water monitoring by coimmobilization
B. subtilis
and
T. cutaneum
in the sol-gel-derived composite material, which is composed of silica,
the grafting copolymer of poly(vinyl alcohol) and 4-vinylpyridine (PVA-
g
-P(4-VP)).
B. subtilis
still retains suffi cient enzymatic viability and activity for biooxidation of organic
materials even when it is killed by a short exposure to high temperature. Therefore, thermally
killed
B. subtilis
can also be used to prepare BOD biosensor, and this biosensor can be stored in
phosphate buffer solution at room conditions without BOD or nutrients even for extended periods
of time, while most of the microbial BOD sensors would require BOD and addition of nutrients to
sustain the living microorganisms [4]. Tan et al. [97] adopted a thermal method to kill
B. subtilis
and used it for sensing BOD of waters and wastewaters. The BOD sensor is fabricated by covering
a dissolved oxygen probe with a biofi lm containing the dead cells, and the measured BOD
5
data of
industrial and synthetic wastewater samples matched well with the results obtained by the conven-
tional American Public Health Association (APHA) method.
14.1.2.3
Bacillus licheniformis
B. licheniformis
is another species of
Bacillus
that belongs to aerobic bacteria. Tan et al. [98] reported
that
B. licheniformis
demonstrated a better ability to assimilate amino acids; therefore it was used to
fabricate glutamate BOD biosensors. Suriyawattanakul et al. [99] coimmobilized
B. licheniformis
and
T. cutaneum
to achieve a great response to glucose on top of the Tefl on membrane of a Clark
oxygen electrode and to form a glucose or glutamate BOD biosensor with improved sensitivity and
dynamic range. It is shown that a membrane loaded with
T. cutaneum
at 1.1
10
8
cells mL
-1
cm
-2
×
10
8
cells mL
-
1
cm
-
2
gave the optimum result.
Jiang et al. [100] immobilized
B. licheniformis
and two other kinds of microorganisms,
Dietzia
maris
and
Marinobacter marinus
, on a PVA organically modifi ed silicate (ORMOSIL) fi lm embed-
ded with an oxygen-sensitive Ru complex to form a glucose/glutamate BOD biosensor; the biosen-
sor is applied for the BOD determination of seawater. This kind of BOD biosensor has a relatively
long life, which could steadily perform up to 10 months.
and
B. licheniformis
at 2.2
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