Biology Reference
In-Depth Information
ability of the gold nanocomposite material, especially in nanoAu
(7.5%)-GEC, since the fluorescence pattern is related to the isolated
goldNPsinsteadofthegoldaggregateswhenincreasingtheamount
of goldNPsfrom 7.5 to 100%.
From the electrochemical evaluation of the electrodes, it can be
concluded that gold is more available for the electrochemical oxi-
dation in the nanoAu(7.5%)-GEC electrode and is present mostly as
NPs, instead of aggregates, showing the characteristic anodic peak
currentnear
+
1.1V(vs.Ag/AgCl)[100].Thevoltammetryforavari-
etyofredoxmoleculesatDNA-modifiedelectrodescanprovideaddi-
tional qualitative information about the system's organization on
the surface. The voltammetric reversibility of highly charged redox
ions is markedly influenced by the attractive/repulsive interactions
with the polyanionic DNA layer that the ions must penetrate to
reach the electrode surface, in the case of highly packed DNA mono-
layers [101]. The voltammetry for the ferrocyanide (3
−
/
4
−
)redox
markersattheDNA-modifiednanoAu-GECisslightlyaffectedbythe
electrostatic interactions with the polyanionic layer, in contrast to
previous reported results for SAMs of DNA in continuous gold elec-
trodes [101], confirming the laxity of the DNA layer created on the
nanoAu(7.5%)-GEC electrode. These data suggest an architecture
thatismadeupofadisperselayerofoligonucleotideimmobilizedon
theisolatedgoldNPsandconfirmsthemicroscopicpatternachieved
by SEM andfluorescence microscopy [99].
Instead of SAMs on continuous layers of gold, isolated gold NPs
areabletoproduce“bioactivechemisorbingislands”fortheimmobi-
lization of thiolated biomolecules, avoiding stringent conditions for
surface coverage as well as the use of auxiliary reagents such as lat-
eralspacerthiols.Lesscompactlayersarethusachievedfavoringthe
biologicalreactiononbiosensingdevices.Hybridizatione
ciencyis
expected to be higher on the edging of the gold NPs surrounded by
nonreactive graphite-epoxy composite.
Briefly,theprocedureconsistsofthefollowingsteps,asschemat-
ically outlined in Fig. 3.7: (i) thiolated probe immobilization by
chemisorption (Fig. 3.7A); (ii) hybridization with the complemen-
tary probe modified with either biotin or digoxigenin (Fig. 3.7B1);
(iii) enzyme labeling of the DNA duplex using streptavidin-HRP
or anti-DIG-HRP (Fig. 3.7C); and (iv) amperometric determination
