Biology Reference
In-Depth Information
solution pH 4.8 [25] is put onto the surface of a GEC electrode in
an upright position. The immobilization of the probe was allowed
to proceed for 15 min without applying any potential under static
conditions.
After the inosine-modified DNA probe immobilization, the DNA
target was detected by the intrinsic DNA oxidation signal coming
from the guanine moieties, as schematically outlined in Fig. 3.4.
Briefly, the procedure consists of the following four steps: [83] (i)
electrochemical pre-treatment of the GEC transducer; (ii) inosine-
substituted probe immobilization by wet adsorption on GEC trans-
ducer; (iii) hybridization with the target; and (iv) electrochemical
determination based on differential pulse voltammetry (DPV), in
which the oxidation signal of guanine (or adenine) was measured
by scanning from
+
0.30 to
+
1.20V at a pulse amplitude of 100 mV
and a scan rate of 15 mV/s. This procedure was demonstrated to be
usefulforthedetectionofIS200elementspecificfor
Salmonella
spp.
[83].
Although a thick or a thin layer of DNA can be attached on the
surface during dry adsorption by controlling the concentration of
the DNA solution being dried, the wet adsorption normally yields
athinDNAlayer.LesscompactDNAlayerswithwidergapsexposing
free-GEC surface are normally obtained during wet adsorption. As
a consequence, the thin-layer DNA/GEC surface required blocking
treatment to avoid non-specific adsorption. During wet adsorption,
the substrate is progressively modified with negative charges com-
ingfromtheDNAbeingadsorbed;thus,rejectingthesuccessiveDNA
molecules that are approaching the substrate. Wet adsorption thus
leads to a “self-control” surface coverage and is less stringent than
dry adsorption [25].
3.4.3
Electrochemical Genosensing Based on
Graphite-Epoxy Biocomposite Modified with Avidin
(Av-GEB) as Electrochemical Transducer
A rigid and renewable transducing material for electrochemical
biosensing, based on avidin bulk-modified graphite-epoxy biocom-
posite (Av-GEB), can be easily prepared by adding a 2% avidin
(or streptavidin) in the formulation of the composite and using
