Biology Reference
In-Depth Information
performances of each, in order to choose the approach that is the
best compromise in terms of sensitivity, specificity, analysis time,
and costs.
Thehighsensitivitiesrequestedbytheaptamer-basedassaysfor
the detection of the target analytes cannot be reached by a “direct
format,”sincethea
nitiesofaptamersfortheirtargetsarenothigh
enough,rangingfromthemicrotothenanomolarlevel.Forthispur-
pose,severalstrategieshavebeenusedassignalamplificationtools,
suchasmetallicandmagneticnanoparticles(NPs),enzymaticlabels,
and quantumdots.
The potential use of aptamers as receptors in biosensors and
bioassays has been extensively reviewed [1-7] and also several
topics have appeared in the last years [8, 9]. In this chapter, the cur-
rentstatusofresearchinelectrochemicalaptasensorsisconsidered.
Attention is focused on label-free and labeled aptasensors, and the
analytical capabilities of these devices are discussed.
2.2 Electrochemical Detection Strategies
Based on Labeling
Labels such as enzymes, NPs, and redox species, such as fer-
rocene (Fc) or methylene blue (MB), are often used for recognition
processes. Electrochemical aptasensors with a label have received
and yet continue to receive considerable attention because they
combine the specificity of the aptamer-analyte recognition to the
advantages of an amplified signal. These strategies are generally
highlysensitiveduetotheanalyticalcharacteristicsofthelabelused.
Labels are commonly covalently linked to terminal groups of
aptamers. The labeling position has to be carefully chosen so as not
tointerferewiththefoldingoftheaptamerand,thus,nottolosethe
bioactivityor stability.
Among the most used labels are enzymes, such as peroxidise
(HRP), glucose oxidase (Gox), and alkaline phosphatase (AP), that
generate an electroactive product close to the transducer surface;
the formation of a relatively high local concentration of the enzyme
product leads to a significantsignalamplification.
