Biomedical Engineering Reference
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nm
nm
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50
40
40
nm
2000
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30
1500
nm
20
1000
20
1000
10
500
500
10
0
0
0
0
0
(a)
(b)
FIGURE 13.5
AFM images of Prussian blue-modifi ed monocrystalline graphite: (a) conventional
Prussian blue deposited without surfactants, (b) Prussian blue electrochemically deposited through liquid
crystalline phase of non-ionic surfactant Brij-56.
Fig. 13.5. As seen, a conventional Prussian blue fi lm is of polycrystalline structure,
however, the layer covers the surface completely.
When Prussian blue has been growing through the liquid crystalline template of
non-ionic surfactant, the corresponding AFM-image (Fig. 13.5b) displays an archi-
pelago of new structures, which may be attributed only to ferric hexacyanoferrate
[144]. These structures of submicron dimensions are surrounded by very smooth areas,
which, taking into account polycrystalline Prussian blue morphology (Fig. 13.5a), dis-
plays an obviously unmodifi ed graphite surface.
The analytical performance of Prussian blue-modifi ed electrodes in hydrogen per-
oxide detection were investigated in a fl ow-injection system equipped with a wall-jet
cell. Nano-structured Prussian blue-modifi ed electrodes demonstrate a signifi cantly
decreased background, which results in improved signal-to-noise ratio.
Nano-structuring also results in a decreased detection limit. Since the latter has dif-
ferent explanations in analytical literature, we defi ne it as the lower limit of the linear
calibration range. For nano-structured Prussian blue the detection limit was found to
be of 1
10
9
mol L
1
(Fig. 13.6).
Since among the main disadvantages of peroxidase-based H
2
O
2
sensors is the sat-
uration of the enzyme with substrate, linear calibration range never reaches the four
orders of magnitude of H
2
O
2
concentrations. It was essential therefore to investigate
the upper detection limit of nano-structured Prussian blue. It is seen that the linear
calibration range is extended over
seven
orders of magnitude for H
2
O
2
concentration
(1
10
2
mol L
1
). The signifi cant deviation from the linearity is observed
only at decimolar (0.1 mol L
1
) hydrogen peroxide content.
The resulting Prussian blue-based nano-electrode arrays in FIA demonstrate a sub-
ppb detection limit (1
10
9
-1
10
9
mol L
1
) and a linear calibration range starting from the
detection limit and extending over seven orders of magnitude of H
2
O
2
concentrations
(1
10
2
mol L
1
), which is the most advantageous analytical perform-
ance in electroanalysis. As a conclusion from the evidence in this chapter, Prussian
10
9
1
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