Chemical and biological sensors based on electroactive inorganic polycrystals - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 421

and selectivity are reached in the case of Prussian blue. Compared with platinum, still
the most widely used transducer, Prussian Blue is three orders of magnitude more
“active”, and three orders of magnitude more “selective”. Moreover, the cost of raw
materials, which is highly important for mass production, is also about three orders of
magnitude less in the case of Prussian blue. The catalytic parameters show promise that
on the basis of Prussian blue a highly advantageous H 2 O 2 transducer can be structured.
13.4.3 An advanced sensor for hydrogen peroxide based on Prussian blue
The likelihood of selective detection of hydrogen peroxide by its reduction in the pres-
ence of oxygen using Prussian blue-modifi ed electrodes was fi rst announced by our
group in 1994 [118]. Indeed, analytical performances of Prussian blue-modifi ed elec-
trodes in hydrogen peroxide detection investigated in fl ow-injection system equipped
with a wall-jet cell, show the linear calibration range prolonged over four orders of
magnitude of hydrogen peroxide concentration. The lower limit of the linear calibra-
tion range referred to as the detection limit is 10 7 mol L 1 . Using Prussian blue as
transducer for hydrogen peroxide it was possible to achieve the sensitivity in fl ow-
injection mode of 0.6A L mol 1 cm 2 [114, 119], which taking into account the
dispersion coeffi cient [120] corresponds to the sensitivity of 1-2 A L mol 1 cm 2 in
either batch regime or under continuous fl ow. The latter is at the upper sensitivity level
limited by hydrogen peroxide diffusion [112].
13.4.4 Non-conductive polymers on the surface of Prussian blue
modifi ed electrodes
Further improvement of the Prussian blue-based transducer presents two principal
problems. First, Prussian blue layers are not mechanically stable, especially on smooth
electrode surfaces because of their polycrystalline nature. Second, despite the low elec-
trode potential used, the most powerful reductants like ascorbic acid still interfere with
sensor response if present in excessive concentrations.
To improve the stability and selectivity, additional electrode coverings were consid-
ered. Conducting and non-conducting polymers were known to reduce the interference
effect. Covering the electrode with Nafi on [37, 121], sol-gel [122, 123] or other thick
fi lms [124] facilitated an increase in sensor selectivity by approximately ten times.
Electrosynthesis of polymers compares favorably with the thick fi lm method pro-
viding addressable and controlled deposition. In terms of selectivity to hydrogen per-
oxide in the presence of interferents, the most promising results were obtained with
poly-1,2-diaminobenzene (poly-1,2-DAB)-modifi ed electrodes [125].
The possibility for electropolymerization on the top surface of Prussian blue fi lms
was probably fi rst shown in [126] describing the high oxidizing ability of Berlin green,
the fully oxidized form of Prussian blue. Afterwards non-conducting polymers were
synthesized on the top surface of transition metal hexacyanoferrate-modifi ed elec-
trodes for immobilization of the enzyme [127].
In contrast to metal surfaces, the growth of non-conducting polymers on the top
surface of Prussian blue-modifi ed electrodes can be independently monitored due to