Biomedical Engineering Reference
In-Depth Information
At the same time the HRP-Fe(II) oxidation peak disappeared. However, at the EPG or
EPG coated with agarose hydrogen in the potential range scanned, the direct reduction
of H
2
O
2
could not be observed. This indicated that the reduction of H
2
O
2
was cata-
lyzed by HRP entrapped in agarose fi lm. The reduction peak current increased with
increasing concentration of H
2
O
2
. The calibration curve gradually tended to a plateau
and then dropped down with adding H
2
O
2
, implying a progressive enzyme inactivation
in the presence of higher concentration of H
2
O
2
.
Biogenic amines, including catecholamines such as dopamine, norepinephrine,
epinephrine, and indoleamines such as serotonin, are neurotransmitters that have spe-
cial roles in neuroscience. An amperometric biosensor using a carbon paste electrode
modifi ed with horseradish peroxidase (HRP) enzyme can be used for total biogenic
amine determinations [247]. The HRP immobilization on graphite was made using
bovine serum albumin, carbodiimide, and glutaraldehyde. The biosensor response
was optimized using serotonin and it presented the best performance in 0.1 M phos-
phate buffer (pH
7.0) containing 10
µ
M of hydrogen peroxide. Under optimized
50 mV, a linear response range from 40 to 470 ng ml
1
was
obtained. The detection limit was 17 ng ml
1
and the response time was 0.5 s. The pro-
posed sensor presented a stable response during 4 h under continuous monitoring. The
difference of the response between six sensor preparations was
operational conditions at
2%. The sensor was
applied in the determination of total biogenic amines (neurotransmitters) in rat blood
samples with success, obtaining a recovery average of 102%.
17.3.2.2 Biosensors based on direct electron transfer of catalase
Catalase is a heme protein belonging to the class of oxidoreductases with ferripro-
toporphyrin-IX at the redox center, and it catalyzes the disproportionation of hydrogen
peroxide into oxygen and water without the formation of free radicals.
Catalase was immobilized with gelatin by means of glutaraldehyde and fi xed on a
pretreated Tefl on membrane served as enzyme electrode to determine hydrogen perox-
ide [248]. The electrode response reached a maximum when 50 mM phosphate buffer
was used at pH 7.0 and at 35ºC. Catalase enzyme electrode response depends line-
arly on hydrogen peroxide concentration between 1.0
10
5
and 3.0
10
3
M with
response time 30 s.
Catalase, which was adsorbed on the surface of multi-wall carbon nanotubes
(MWNTs), could show the direct voltammetry and electrocatalytic properties [249].
The catalase MWNTs-modifi ed GC electrode has excellent and strong mediation
properties and facilitates the low potential amperometric measurement of hydrogen
peroxide. An obvious catalytic reduction peak appears at the potential of
0.25 V for
the catalase MWNTs-modifi ed GC electrode when H
2
O
2
was added to the solution.
By increasing the concentration of H
2
O
2
, the cathodic peak current of catalase
increased while its anodic peak current decreased. The catalytic currents increased
linearly with the H
2
O
2
concentration in the range of 10
M to 1 mM. The linear
regression equation of catalytic currents vs hydrogen peroxide concentration can
be obtained from the experimental data:
I
p
(
µ
µ
A)
6.563[H
2
O
2
] (
µ
M)
18.3 with a
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