Biology Reference
In-Depth Information
An alternative approach to antibody fragments followed the discovery
of camelid and shark antibodies, composed only of single heavy chains with
very small antigen-binding domains.
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This discovery facilitated the devel-
opment of thermostable antibodies that retain specificity. Regions from these
antibodies have been cloned and expressed as 12-15kDa single-domain
antibodies (sdAbs) that are stable to temperatures as high as 90 °C. In 2007,
Sherwood et al. developed an unoptimized chemiluminescent assay; the
most specific clone could detect 0.1-1 pfu per well of Ebola virus antigens
within 30 min.
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These highly sensitive and selective sdAb probes could be
used in any antibody-based biosensor designed to detect infectious agents.
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Phage antibody technology has also been developed, offering advantages
over traditional antibodies in terms of specificity, sensitivity, and robustness.
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In this approach, a fragment of the antibody is produced and displayed on
the surface of a bacteriophage.
7.2.2. Alternative recognition elements
This section will provide a short introduction to other types of recognition
elements, including peptides, enzymes, carbohydrates, DNA/RNA, aptam-
ers, whole cells, and biomimetics.
Peptides are short chains of amino acids and could therefore be consid-
ered to include antibody fragments. Other types of peptides of interest as
recognition elements in biosensors include antimicrobial peptides (AMPs),
which play an important role in the immune system response to pathogen
infection. AMPs consist of 15-45 amino acids and semiselectively bind to
microbial surfaces. However, there are two main problems encountered
with this type of recognition element. First, there is the antimicrobial activ-
ity, which can destroy the pathogens of interest. Second, since AMP target
interaction is primarily electrostatic, these probes are particularly sensitive
to changes in solution ionic strength, which is likely to be especially disad-
vantageous for environmental applications.
Enzymes have been commonly used in biosensors, as they are highly
specific.
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However, disadvantages include the expense and instability of
purified enzymes. Recently, genetically engineered enzymes have been
applied to enhance the sensitivity and selectivity of enzyme-based biosen-
sors, through a variety of strategies e.g. introducing modifications to increase
the accessibility of the active site, to improve surface immobilization, or to
enhance the electron transfer capabilities.
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DNA/RNA biosensors are based on the interaction between a nucleic
acid target and its complementary probe and widely used for the detection
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