Biomedical Engineering Reference
In-Depth Information
TABLE 20.2
Advantages of Aptamers Over Antibodies
Antibodies
Aptamers
Requires the use of animals
No animals required
Limitations against nonimmunogenic
Can be generated against nonimmunogenic and
and toxic substances
toxic substances
Kinetic parameters cannot be modified on demand
Kinetic parameters can be modified on demand
Labeling can cause loss of affinity
Variety of reporter molecules can be attached
without affecting binding properties
Not feasible to identify antibodies that interact
Selection conditions can be modified to select
with targets under nonphysiological conditions
aptamers with particular properties
Problems with batch to batch variation
Little or no batch to batch variation
Limited shelf-life, temperature sensitive
Stable in long-term storage, can be transported
and susceptible to denaturation
at ambient temperature and can be regenerated
after denaturation
Source:
Modified from O'Sullivan CK. 2002. Aptasensors—the future of biosensing?
Analytical and Bioanalytical
Chemistry
372: 44-48.
20.3.4
Applications
20.3.4.1 Two Site Binding Assays
ELISA sandwich assays, using antibodies, are a very common diagnostic assay. The term
enzyme-linked oligonucleotide assay (ELONA) is applied to the same assay format using
aptamers (51). Various ELONA formats can be adopted, using for example (51):
Aptamers as capture molecules and antibodies as reporter molecules.
●
Antibodies as capture molecules and labeled aptamers against the antibody-
antigen complex as reporter molecules.
●
Aptamers as capture molecules and labeled aptamers against the aptamer-
analyte complex as reporter molecules.
●
ELONAs have been demonstrated to be successful for the detection of VEGF (61) and
CD4
cells (62).
20.3.4.2 Flow Cytometry
Flow cytometry is a powerful tool that is used both analytically and diagnostically for the
multiparameter analysis of cells in suspension. Generally, this method is performed using
labeled monoclonal antibodies. Recently however, aptamers have been used to perform
the role of monoclonal antibodies in this process, with promising results. Indeed, it has
been shown that aptamers can be relatively easily conjugated to small fluorophores, such
as fluorescein, or even to larger proteins such as phycoerythrin, and still retain their bind-
ing characteristics, demonstrating their ability to be used with a wide variety of reporter
molecules that are generally used in diagnostics (52). Generally, aptamers have been
shown to perform as well as antibodies or can even be used in combination with them for
flow cytometry analyses (52).
20.3.4.3 Biosensors
Affinity sensors should ideally fulfill at least three basic criteria (52), namely:
The ability to transduce the binding event without adding extra reagent.
●
The ability to detect and quantify the target within the desired concentration
range and time period.
●
The ability to make repeated measurements on the same transducer.
●
