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was added to the electrode. p-Aminophenyl phosphate (p-APP) was
used as enzymatic substrate and differential pulse voltammetry as
electrochemical technique. The results obtained with the electro-
chemical aptasensor were compared with those based on an ELISA-
type assay (ELONA). The aptasensor showed high specificity and
selectivity toward IgE with a detection limit of 23 ng/mL, which is
a concentration su
cient for detection of IgE in blood considering
that the IgE concentration in blood samples of healthy subjects is in
the range 240 to 290 ng/mL. Moreover, in this work the stability of
the assay performed using the aptamer against IgE was compared
with that of the assay carried out with a monoclonal antibody spe-
cific for IgE. Authors reported that the assay performed using the
aptamer was more stable than that with antibody, considering that
aptamers can be easily regenerated by also using harsh conditions
and are thermo-stable, because the aptamer folding is not affected
by the temperature.
Among the several strategies reported by Mir
et al.
[17] for the
detection of thrombin, an electrochemical aptasensor based on a
competitive assay resulted to be the most sensitive. Thrombin was
immobilized on gold-mercaptoethanol-treated electrodes by pas-
sive adsorption and then the modified electrodes were incubated
with a biotinylated aptamer anti-thrombin. The sensor was subse-
quently incubated with streptavidin-horseradish peroxidase conju-
gate, which bound to the biotin on the aptamer. The aptamer was
quantifiedbytheelectrochemicaldetectionofthereactioncatalyzed
by the peroxidase. Hydrogen peroxide was used as oxidizing agent
and [Os(bpy)
2
(pyr-CH
2
-NH
2
)]Cl as mediator. In this case the limit
ofdetectionofthrombinwas3.5nM.Thrombinwasimmobilizedby
direct adsorption also on bare gold electrodes and on polystyrene
surfaces but it was not detectable on these unmodified surfaces.
It was supposed that in these surfaces the adsorption position of
thrombin created steric impediments preventing the subsequent
binding with the aptamer; alternatively, the binding of thrombin to
the surfaces may have denatured the protein.
Centi
et al.
[18] described various approaches for the devel-
opment of electrochemical aptasensors for the detection of
thrombin using magnetic beads as solid support and carbon
