Biomedical Engineering Reference
In-Depth Information
Cobalt hexacyanoferrates and Prussian blue have shown high activity in oxidations
of hydrazine and hydroxylamine [80-82]. Electrocatalytic activity in this reaction has
also been found for nickel [83] and manganese [69] hexacyanoferrates.
Ten years ago oxidation of NADH [84, 85] seems not to be important because of
the other more powerful electrocatalysts [86-89]. A possibility for oxidation of gua-
nine even in DNA [90] with cobalt hexacyanoferrate, on the contrary, seems to be more
apposite.
In contrast to a variety of oxidizable compounds, only a few examples for the detec-
tion of strong oxidants with transition metal hexacyanoferrates were shown. Among
them, hydrogen peroxide is discussed in the following section. Except for H
2
O
2
, the
reduction of carbon dioxide [91] and persulfate [92] by Prussian blue-modifi ed elec-
trode was shown. The detection of the latter is important in cosmetics. It should be
noted that the reduction of Prussian blue to Prussian white occurs at the lowest redox
potential as can be found in transition metal hexacyanoferrates.
13.4 ADVANCED SENSOR FOR HYDROGEN PEROXIDE
13.4.1 H
2
O
2
as important analyte for medicine, biology, environmental
control, and industry
Monitoring of hydrogen peroxide is of great importance for modern medicine, envi-
ronmental control, and various branches of industry. H
2
O
2
is a chemical threat agent;
its excessive concentration as a product of industry and from atomic power stations
affects the environment [93, 94]. In addition, hydrogen peroxide is used for the disin-
fection of water pools, food, and beverage packages [95, 96], which makes it important
to measure its residual concentration. On the other hand, H
2
O
2
is the most valuable
marker for oxidative stress, recognized as one of the major risk factors in the progres-
sion of disease-related pathophysiological complications in diabetes, atherosclerosis,
renal disease, cancer, aging, and other conditions [97-101]. Except for oxidative stress,
H
2
O
2
is the most valuable marker for infl ammatory processes [102], and a mediator for
apoptotic cell death [103, 104].
Selective detection of hydrogen peroxide is also of great importance for biosensors.
More, than 90% of enzyme-based biosensors and analytical kits use the enzyme oxi-
dase as a terminal (signal generation) one. Operation of biosensors requires succes-
sive coupling of the enzyme and electrochemical reactions. As stated,
fi rst-generation
biosensors are based on direct electrochemical detection of substrate or product of
the enzyme reaction. In the case of oxidases, these are oxygen and hydrogen perox-
ide, respectively. Amperometric detection of these substances was usually undertaken
using platinum or platinized electrodes [105-108]. Detection of oxygen consumption
at negative potentials (
0.6 V vs Ag/AgCl) [105, 106] was the most simple proce-
dure. Nevertheless, such biosensors were not able to detect low analyte concentrations.
The reasons were: (i) great excess of oxygen, (ii) variation of oxygen concentrations
in biological liquids, and (iii) reduction of hydrogen peroxide at similar potentials.
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