Chemical and biological sensors based on electroactive inorganic polycrystals - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 430

calibration plot is linear over four orders of magnitude of glucose concentration from
0.1 M to 1 mM. The sensitivity of FIA glucose detection, which has been calculated in

the linear range up to 1 mM, is of 0.05 A M 1 cm 2 . This is only ten times lower than
the sensitivity of the transducer to hydrogen peroxide used in this biosensor [164].
Let us compare the elaborated biosensor with the glucose sensitive electrodes using
a similar transducer. Considering the immobilization of glucose oxidase in poly(vinyl
alcohol) grafted 4-vinylpyridine [182], in an additional metal hexacyanoferrate layer
during electrodeposition [149], covering by Nafi on membrane [160], in gelatin gel
[159], and in poly(o-phenylenediamine) during electropolymerization [127], one
concludes that the proposed approach displays a dramatic (100-fold) improvement in
sensitivity of the resulting biosensor. Moreover, a comparison with the other known
biosensors for glucose [183-187] has shown that the proposed sensor is characterized
by the best analytical performances [164].
Combined with the attractive performance of a Prussian blue-based hydrogen per-
oxide transducer, the proposed immobilization protocol provides elaboration of the
most advantageous fi rst-generation glucose biosensor concerning its sensitivity and
detection limit.

µ

13.6 CONCLUSIONS

In conclusion, the unique properties of Prussian blue and other transition metal hexa-
cyanoferrates, which are advantageous over existing materials concerning their ana-
lytical applications, should be mentioned. First, metal hexacyanoferrates provide the
possibility to develop amperometric sensors for non-electroactive cations. In contrast
to common “smart materials”, the sensitivity and selectivity of metal hexacyanofer-
rates to such ions is provided by thermodynamic background: non-electroactive cati-
ons are entrapped in the fi lms for charge compensation upon redox reactions.
Second, Prussian blue is considered the most advantageous low potential transducer
for hydrogen peroxide not only among hexacyanoferrates, but over all known systems.
The specifi c activity and, thus, the sensitivity of Prussian blue-modifi ed electrodes to
H 2 O 2 reduction in neutral media are characterized by the electrochemical rate constant
of 0.01 cm s 1 , which is three orders of magnitude (!) higher than in the case of plat-
inum, being the most widely used hydrogen peroxide transducer. Selectivity in H 2 O 2
reduction on Prussian blue-modifi ed electrodes relative to oxygen is three orders of
magnitude (!) higher than in the case of platinum. Besides that, raw materials required
for Prussian blue-based sensors are three orders of magnitude less expensive than for
noble metal-based or enzyme-based sensors. Except for greatly improved sensitivity (up
to 1 A M 1 cm 2 ) and selectivity, the specially deposited and post-treated Prussian blue-
modifi ed electrodes possess quite satisfactory long-term operational stability compared
to or even exceeding that of the known transducers. Prussian blue-modifi ed electrodes
are ready to use in analytical devices for either sampling or continuous monitoring of
chemical threat agents, important food additives, and key metabolites of life pathways.
The particular importance of application of Prussian blue-based biosensors is expected