Biomedical Engineering Reference
In-Depth Information
against molecules that are not inherently immunogenic can therefore be prob-
lematic.
The production and identification of monoclonal antibodies are laborious proce-
dures and are likely to be costly in searches for rare antibodies requiring the
screening of large numbers of colonies.
High yields of antibodies may be problematic to obtain due to difficulties asso-
ciated with growing certain hybridomas in vivo, the manner in which high
yields are typically achieved.
The performance of the same antibody may vary between batches, requiring the
immunoassay to be reoptimized with each new batch of antibody.
It is not feasible to identify antibodies that could detect targets under nonphysi-
ological conditions.
There is no control over the selection of the target protein to which the antibody
binds (this is “determined” by the immune system of the animal) (54).
The kinetic parameters of antibody-target interactions cannot be manipulated
on demand.
Antibodies are heat-labile, undergoing irreversible denaturation.
They have a limited shelf-life.
It is important to note that various approaches addressing the shortcomings listed above
are being investigated, including humanization of antibodies, antibody engineering, and
in vitro immunization (52).
Listed below are the various advantages aptamers offer over antibodies for the use in
analytical and diagnostic devices (52):
Aptamers do not require the use of animal systems for their production.
The properties of aptamers can be changed on demand due to the fact that they
are produced through an in vitro process that does not depend on animals or on
in vivo conditions.
Selection conditions can be manipulated to obtain aptamers that bind the target
under nonphysiological conditions, for example. Similarly, the kinetic parame-
ters of the aptamer can also be manipulated on demand.
Aptamers can be generated against targets that are toxic or that are not inher-
ently immunogenic.
Batch to batch variation is eliminated in aptamer production, given the fact that
they are chemically synthesized.
Aptamers can be easily engineered to include reporter molecules at a precise
location, specified by the user, without affecting their binding characteristics.
Small aptamers can be used to generate dense receptor layers, thus allowing
increased sensitivity for a given affinity (31).
The heat denaturation process in aptamers is reversible, allowing them to be eas-
ily regenerated.
Aptamers are stable in long-term storage.
The main advantages of aptamers over antibodies are summarized in Table 20.2.
The main drawbacks of aptamers include the time required for selection using a manual
SELEX process, although this is slowly being overcome by the introduction of automated
SELEX processes. Additionally, their affinity constants are generally lower than those of
antibodies and their structural stability is still questionable (19). Furthermore, the fact that
the science of aptamers is relatively young and much of the work and knowledge base in
the field is still highly experimental is an additional concern hindering their common use.
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