Biology Reference
In-Depth Information
An example of electrochemical sandwich assay for detection of
immunoglobulin E (IgE) is reported [14]. The assay was performed
by coupling an antibody against IgE with an aptamer anti-IgE.
Antibody molecules were covalently immobilized as capture probe
on gold electrodes via a self-assembled monolayer of cysteamine
throughtheglutaraldehyde-basedbifunctionallinking.Afterthatthe
target was captured, the biotinylated anti-IgE aptamer was added
because it could interact specifically with the analyte, followed by
the addition of a streptavidin-alkaline phosphatase (streptavidin-
AP) solution. Once biotin-streptavidin recognition occurred, the
signal amplification was achieved based on enzymatic silver depo-
sition. Ascorbic acid 2-phosphate was converted by AP into ascor-
bic acid, a strong reducing agent. It could reduce the silver ions in
the solution to silver metal that preferentially deposited on the gold
surface of electrodes. The amount of deposited silver, which is pro-
portionaltotheamountofIgEtargetboundontheelectrodesurface,
was quantifiedby linear sweep voltammetry.
Thedetectionlimitcalculatedusingthisapproachwas0.02nMof
thrombin. A similar approach was reported by Degefa and cowork-
ers [15] as well.
2.4 Electrochemical Aptasensors Based on
a Competitive Assay
In literature no many examples of electrochemical enzyme-labeled
aptasensors based on a competitive assay are present. The advan-
tagesofacompetitiveformat(directandindirect)aremainlyrelated
to the fact that only one aptamer is required (considering that two
ormoreaptamersarenotselectedformanytargetanalytes)andthe
time necessary for theassay is faster.
A disposable electrochemical competitive assay for detection
of IgE was proposed by Papamichael
et al.
[16].Inthisworkthe
IgE antigen was immobilized on the surface of screen-printed elec-
trodes, then a competition step between IgE bound to the electrode
surface and IgE in solution for the biotinylated aptamer was left to
occur. At this point the streptavidin-alkaline phosphatase conjugate
