Biology Reference
In-Depth Information
papillary thyroid carcinomas at a detection limit of 0.35 aM.
Selvaraju
et al.
[42] realized a drawback of the gold autocatalytic
process is that special care is required in the control of deposition
time and temperature to achieve a high signal-to-background ratio
Instead, they used DNA-labeled gold nanoparticles to catalyze the
reduction of
p
-nitrophenol to electroactive
p
-aminophenol. The
p
-aminophenol can be catalytically cycled back to
p
-nitrophenol
at a ferrocene-modified indium-tin oxide (ITO) electrode, offering
large signal amplification. The high signal amplification and low
background current enabled the detection of 1 fM target DNA.
Willner's group has used platinum-nanoparticle labeled DNA where
the nanoparticles catalyzed the reduction of H
2
O
2
with a detection
limitof 10 pM for the hybridization[43].
8.4 Voltammetric Detection of Metal-Nanoparticle Labels
Voltammetry is of interest as a detection method for DNA due to
the fact that it provides high sensitivities and that the equipment
required is relatively cheap in comparison with techniques such
as fluorescence, surface plasmon resonance, and microfabricated
cantilevers, while safety issues exist with radioactive labels. Below
we summarize the voltammetry theory necessary to develop and
test DNA sensors.
8.4.1
Principles of Analytical Voltammetry
The principle of analytical voltammetry is that the current
I
from a
redox reaction is recorded under conditions of controlled potential
and is used to calibrate the concentration of the reacting species.
The electrode potential is set relative to a reference interface
which ideally does not change potential as the voltage applied
across the cell is changed. To exhibit this property the current
across the interface during equilibrium should be high. Common
reference interfaces are Ag/AgCl/KCl
sat
and Hg/Hg
2
Cl
2
/KCl
sat
.To
completethecurrentpathforthereactionathirdelectrodeisusually
incorporated, but two-electrode cells can also be used by passing
current through the reference, provided that current is in the order
