Biology Reference
In-Depth Information
the analyte is bound to the aptamer molecules immobilized on the
electrode surface and interacts also with MB, an increased redox
current is recorded. Hianik
et al.
[31] first reported an electrochem-
ical aptasensor for the detection of thrombin based on the inter-
action of MB with the aptamer-thrombin complex. A biotinylated
DNA aptamer was immobilized on a gold electrode via streptavidin-
biotin interactions. When thrombin was bound to the immobilized
aptamer and MB interacted with thrombin, measurable changes of
charge transfer measured by differential pulse voltammetry (DPV)
were obtained. However, since MB can also non-specifically bind to
the DNA aptamer and streptavidin, the background signal and sig-
nal changes were high and the detection limit of thrombin obtained
using this approach was relatively low (10 nM).
Recently,anaptasensorbasedonaredoxprobe([Ru(NH
3
)
5
Cl]
2
+
)
was developed for the detection of platelet-derived growth fac-
tor (PDGF) [32]. A sandwich assay format was carried out, since
PDGF has two aptamer-binding sites, which made it possible for
one PDGF molecule to connect with two aptamers simultaneously.
Gold electrodes were modified by immobilization of a thiolated
aptamer against PDGF; then the aptamer-modified electrodes were
incubated first with different concentrations of PDGF and then with
aptamer-loadedAu-NPs.[Ru(NH
3
)
5
Cl]
2
+
molecules,whichwerefur-
therimmobilizedontothesurfaceoftheabove“sandwich”structure
(Fig.2.6),wereusedasredoxprobesandasuitableconcentrationof
the redox probe was optimized. Cyclic voltammetry measurements
wereperformed.Theauthorsreportedthatthesandwichformatand
the use of Au-NPs allowed to amplify the signal of the redox probe
allowing to obtain a very low detection limit (1
10
−
14
Mforpuri-
fiedsamples).Theaptasensorwassuccessfullyappliedtotheanaly-
sis of PDGF in serum samples.
Another commonly used redox probe is Fe(CN)
3
−
/
4
6
which has
been coupled to different electrochemical techniques as summa-
rized in Table2.1.
A very recent example of the use of this redox probe in an
aptamer-based biosensor was published by Kim
et al.
[33]. An
electrochemical biosensor for oxytetracycline detection was devel-
opedusingssDNAaptamerimmobilizedongoldinterdigitatedarray
(IDA) electrode chip (Fig. 2.7). Cyclic voltammetry and square wave
voltammetrywereusedtomeasurethecurrentattheelectrodechip
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