Biomedical Engineering Reference
In-Depth Information
Electrochemical biosensors based on detection of hydrogen peroxide at platinized elec-
trodes were found to be more versatile allowing a decrease in detection limit down to
1
mol L
1
[109]. However, all biological liquids contain a variety of electrochemically
easily oxidizable reductants, e.g. ascorbate, urate, bilirubin, catecholamines, etc.,
which are oxidized at similar potentials and dramatically affect biosensor selectivity
producing parasitic anodic current [110].
Hence, for successful operation of fi rst-generation oxidase-based biosensors the
selective low potential detection of hydrogen peroxide is required. As will be shown,
this is possible only with transition metal hexacyanoferrates. Using a peroxidase enzyme
electrode (peroxidases are responsible in nature for the reduction of hydrogen perox-
ide) [111, 112], one can develop a selective method for the detection of H
2
O
2
. However,
enzymes being biological macromolecules obviously cannot provide long-term sensor
operation due to their inherent instability. Moreover, some commonly found reducing
agents in “real” samples may compete with the electrode as the source of electrons for
the oxidized form of the peroxidase leading to erratic signals.
µ
13.4.2 Advanced electrocatalyst for hydrogen peroxide reduction
Through optimization of the deposition procedure for Prussian blue, a selective electro-
catalyst for H
2
O
2
reduction able to operate in the presence of oxygen in a wide poten-
tial range has been synthesized [11]. Selectivity of Prussian blue in relation to oxygen
is illustrated in hydrodynamic steady-state current potential curves (Fig. 13.3). As seen
in air saturated solution (oxygen concentration is approximately 0.2 mmol L
1
), only a
minor current is observed. However, when the twofold lower concentration of hydrogen
peroxide is added, a well-defi ned polarographic wave with the half-wave potential coin-
cided with the Prussian blue/Prussian white redox potential appears. At the current pla-
teau region, the current of the hydrogen peroxide reduction is two orders of magnitude
80
60
40
20
0
0
100
200
300
E, mV
FIGURE 13.3
Hydrodynamic voltammograms of Prussian blue-modifi ed electrodes in a wall-jet cell
with continuous fl ow of 0.8 ml/min: (
) background in air saturated solution (0.1 M KCl
0.01 M phos-
phate, pH 6.0), (!) 0.1 mM H
2
O
2
.
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