Biomedical Engineering Reference
In-Depth Information
A polyaniline nanoi bers (PANI(nano))/carbon paste electrode (CPE)
was designed by Zhou
et al.
[142] via clopping PANI(nano) in the carbon
paste. Subsequently, a composite comprising nanogold (Au -nano) and
carbon nanotubes (CNT) was bound to the PANI(nano)/CPE surface. h e
loading of the DNA probes on this novel platform was strongly enhanced as
well as the sensitivity for the detection of PCR amplii ed sequences of trans-
genically modii ed beans, achieving a limit of detection of 5.6×10
−13
mol L
−1
.
4.4.2
Gold Nanoparticles Used as Labels
In electrochemical genosensors, gold nanoparticles (AuNPs) have been
widely employed as labels for DNA sequences due to their size, which can
be comparable to that of DNA double helix diameter, and the fact that they
can provide a sensitive electrochemical signal [81].
In impedimetric genosensors, AuNPs were mainly used to achieve an
amplii cation of the analytical signal. In fact, the presence of AuNPs on
the electrode surface strongly inl uence the charge transfer process, thus
increasing the variation of the charge transfer resistance, both for elec-
trostatic repulsion and for sterical hindrance issues. To this end, Bonanni
et al.
[83] used streptavidin-coated gold nanoparticles (strept-AuNPs) to
label biotinylated DNA sequences and amplify the impedimetric signal
generated in a biosensor for the detection of DNA hybridization. With
this system a 90% amplii cation of the impedimetric signal was obtained.
In a similar scheme, the same authors [143] carried out the detection of
double-tagged DNA coming from polymerase chain reaction (PCR) ampli-
i cation of
Salmonella spp
. in real samples. h e amplii cation of impedimet-
ric signal was performed by conjugating the duplex with anti-digoxigenin
antibody from mouse. h is was followed by a secondary labeling with
AuNPs-labeled anti-mouse IgG. In an alternative protocol, an amplii ca-
tion scheme using protein G was also proposed. With the AuNPs labeling,
a detection limit in the fM range was achieved.
h e detection of a synthetic sequence correlated to cystic i brosis was
also performed by Bonanni
et al.
[31] using MWCNTs platform and
strept-AuNPs amplii cation in a sandwich scheme. Dif erent protocols for
the impedimetric detection of DNA hybridization were compared in this
work, i nally achieving a LOD of 100pM.
Moreno-Hagelsieb and coworkers [144] labeled the DNA target with
AuNPs in order to amplify the capacitance recorded between interdigi-
tated aluminium electrodes imprinted over an oxidized silicon wafer. In
addition, a further signal amplii cation was attained by a silver enhance-
ment treatment on the AuNPs.
