Biology Reference
In-Depth Information
could be challenged by safety permissions, especially when the cells have
been genetically modified, although some whole cell-based sensors are
commercially available.
An early example of the use of living systems for detection of harm-
ful agents is that of canaries in coal mines. The canaries were employed as
a means of monitoring the presence of carbon monoxide in the mine. In
recent years, many different cell types have been employed in biosensors,
with bacteria being particularly popular. Mammalian cells have also been
utilized as recognition elements. This was recently reviewed by Banerjee
and Bhunia, with a particular focus on pathogens relevant to food, environ-
ment, medical, and biosecurity applications.
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The unique aspect of this type of sensor is its ability to simulate physiolog-
ical responses in vivo. Another advantage of the whole-cell approach is that
these systems offer sensitivity to a group of pathogens and therefore could
offer a greater ability to detect new and emerging pathogens. Furthermore,
this approach can detect the toxicity of pathogens as opposed to quantitative
concentration determination. As has been particularly interesting for micro-
pollutants, whole-cell biosensors could detect synergistic effects. However, in
water applications the failure of some whole-cell biosensor systems to detect
all pathogens can be a drawback. The presence of nonviable pathogens in
water supplies can indicate problems with treatment systems and is therefore
valuable information. Other disadvantages of whole-cell biosensors are the
specificity, reliability, and roughness; long-term storage and shelf-life; as well
as price.
Biomimetics are chemicals designed to mimic biological recognition,
with one example being molecularly imprinted polymers. These polymers
are synthesized with the intended target, or more commonly an analog of
the target, present. Once the polymer is stably synthesized, these “target”
molecules are washed out, leaving recognition cavities corresponding to the
target. This approach has been widely used for small molecules, though less
so for the detection of whole cells; it has also been combined with biosen-
sors. The advantages of this approach are that these polymers are more stable
and robust than antibodies, although a major drawback can be the design
of an appropriate synthesis route as well as postprocessing of the polymer.
7.2.3. Immobilization strategies
Once a particular recognition element has been selected, the development of
biosensors requires the functionalization of the biosensor surface in order to
incorporate the selected biorecognition elements. This surface immobilization
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