Biology Reference
In-Depth Information
thiol-gold interactions. In the presence of target DNA, a sandwich
was formed between magnetic beads modified with capture
probe DNA, the target DNA, and the detection probe modified
indium/gold nanorods. This is shown schematically in Fig. 14.8A.
Detectionoccurredbyeithersolid-statechronopotentiometryofthe
indium/goldnanorodscollectedatamercury-coatedscreen-printed
carbon electrode by an external magnet, or chronopotentiometric
stripping of the indium label, following dissolution under acidic
conditions, at a mercury-coated carbon-fiber electrode. The use of
the nanorods as labels allowed detection of 30 ng/L (250 zmol)
target DNA.
14.3.2
Nanowires Interfaced with Electrodes as an
Immobilization Matrix
Nanowires have also been used as an immobilization matrix for
probe DNA with inherent enhanced electron-transfer kinetics and
higher surface area. Electroactive reporter molecules are then used
tomeasureimmobilizedDNA.Kelley'sgrouphasreportedaplatform
for electrochemical DNA detection using arrayed gold nanowires
generated by electroless deposition of gold onto polycarbonate
membranes (see Fig. 14.9A), which were exposed by subsequent
oxygen plasma etching (Fig. 14.9B) [42]. Thiolated probe DNA
was deposited onto the gold nanowire array and [Ru(NH
3
)
6
]
3
+
and [Fe(CN)
6
]
3
−
were used as electrocatalytic reporters for the
amount of hybridized target DNA, as shown in Fig. 14.9C, yielding
an attomole-level detection limit. The authors showed that catalytic
currentsanddiffusionalmobilityofRu
3
+
ionsatthenanowirearray
are markedly different than that obtained at bulk macroelectrodes
allowing for improved signal-to-noise ratio and sensitivity [43].
These results demonstrate the utility three-dimensional nanoscale
systems can posses over bulk macroscale systems. Very recently,
Kelley's group reported an extension of their work in which peptide
nucleic acid (PNA) probes were immobilized onto gold nanowire-
modified polycarbonate membranes and again used [Ru(NH
3
)
6
]
3
+
and [Fe(CN)
6
]
3
−
as electrocatalytic reporters [44]. Unlike DNA, the
peptide backbone of the PNA probe resulted in a neutral charged
surfacethatprovidedsignificantlydecreasedbackgroundsignals.In
