Biomedical Engineering Reference
In-Depth Information
0.2
0.6
0.4
0.2
0
0
0.2
(ii)
(i)
0.4
0.2
(iii)
0.6
0.4
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(ii)
0.8
(i)
1.0
1.0
1.2
1.4
1.2
1.4
0.8
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0.6
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0.1
0
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0.8
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0
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(a)
Potential/V vs SCE
(b)
Potential/V vs SCE
FIGURE 17.6 (a) Cyclic voltammograms of the uricase/GCE (i), ZnO/GCE (ii), and uricase/ZnO/GCE
(iii) in PBS (pH 6.9), scan rate: 100 mVs 1 . (b) Cyclic voltammograms of the uricase/GCE (i), ZnO/GCE
(ii), and uricase/ZnO/GCE (iii) in PBS (pH 6.9) containing 5.0 10 4 mol L 1 uric acid, scan rate:
100 mVs 1 . (From [259], with permission.)
An amperometric urate sensor based on uricase-immobilized silk fi broin membrane
was developed by Zhang [256]. The biosensor can be used to measure the urate level
in human serum or urine and standard additions of uric acid. F or this biosensor, the
recoveries of uric acid in human serum and urine are in the range of 94.2
102.6% to
92.5
97.9%, respectively. The relative standard deviations for repeatedly monitoring
standard urate solution, human serum, and urine are 2.37, 3.72, and 2.95%, respec-
tively, based on 100 measurements.
XOD is one of the most complex fl avoproteins and is composed of two identical
and catalytically independent subunits; each subunit contains one molybdenium center,
two iron sulfur centers, and fl avine adenine dinucleotide. The enzyme activity is due
to a complicated interaction of FAD, molybdenium, iron, and labile sulfur moieties
at or near the active site [260]. It can be used to detect xanthine and hypoxanthine by
immobilizing xanthine oxidase on a glassy carbon paste electrode [261]. The elements
are based on the chronoamperometric monitoring of the current that occurs due to the
oxidation of the hydrogen peroxide which liberates during the enzymatic reaction. The
biosensor showed linear dependence in the concentration range between 5.0
10 7
10 5 M for hypoxanthine,
respectively. The detection limit values were estimated as 1.0
10 5 M for xanthine and 2.0
10 5 and 8.0
and 4.0
10 7 M for xanthine
10 6 M for hypoxanthine, respectively. Li used DNA to embed xanthine
oxidase and obtained the electrochemical response of FAD and molybdenum center
of xanthine oxidase [262]. Moreover, the enzyme keeps its native catalytic activity to
hypoxanthine in the DNA fi lm. So the biosensor for hypoxanthine can be based on
and 5.3
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