Biomedical Engineering Reference
In-Depth Information
correlation coeffi cient of 0.9889 and a detection limit of 50
ยต
M at a signal-to-noise
ratio of 3.
Collagen, an electrochemically inert protein, formed fi lms on pyrolytic graphite (PG)
electrodes, which provided a suitable microenvironment for heme proteins to transfer
electrons directly with the underlying electrodes. When catalase was incorporated into
the PG electrode by collagen, it can exhibit electrochemical behavior well and often
was used to catalyze the reduction of nitrite, oxygen, and hydrogen peroxide [250]. For
Cat-collagen fi lms, when a certain amount of air was injected into a pH 7.0 buffer by a
syringe, a signifi cant increase in reduction peak at about
0.5 V was observed, accompa-
nied by the decrease or even disappearance of the oxidation peak of CatFe(II), suggesting
that CatFe(II) had reacted with oxygen. The reduction peak current increased with the
amount of oxygen in the solution. The electrochemical catalytic reduction of hydrogen
peroxide also can be observed on the protein-collagen fi lms by CVs. When H
2
O
2
was
added into the pH 7.0 buffer solution, an increase in the reduction peak was observed
for heme Fe(III), accompanied by the decrease or disappearance of the oxidation peak
for heme Fe(II). The reduction peak current increased linearly with the concentration of
H
2
O
2
. When NO
2
was injected into the pH 5.5 buffer solution, a new reduction peak
was observed at about
0.8 V and the reduction current increased with the concentration
of NO
2
. The detection limit of NO
2
for the Cat-collagen/PG electrode is 3.15 mM.
PAM can absorb large amounts of water and form hydrogel, which is widely used
in the fi eld of life science. When catalase was incorporated into the PG electrode by
PAM, the modifi ed electrode showed good electrocatalytic activity toward dioxygen
and hydrogen peroxide [251]. At Cat-PAM fi lm electrodes, the position of catalytic
reduction peak potential of hydrogen peroxide was almost the same as that of oxygen,
indicating that the reaction mechanism between the two systems was similar. When a
certain amount of oxygen was passed through a pH 7.0 buffer solution by a syringe,
an increase in the reduction peak at approximately
0.5 V was observed for Cat-PAM
fi lms, accompanied by a disappearance of the oxidation peak for CatFe(II). The reduc-
tion peak current increased with the amount of oxygen in solution. Reduction of H
2
O
2
was also electrochemically catalyzed by Cat-PAM fi lms. When H
2
O
2
was added to the
pH 7.0 buffer solution, an increase in the reduction peak at approximately
0.5 V was
observed, accompanied by a disappearance of the oxidation peak. The reduction peak
current increased with the concentration of H
2
O
2
in the solution. Catalytic effi ciency,
expressed as a ratio of the reduction peak current of Cat-PAM fi lms in the presence
(
I
c
) and absence (
I
d
) of H
2
O
2
,
I
c
/
I
d
, decreased with the increase in scan rate.
17.3.2.3 Biosensors based on direct electron transfer of GOD
Glucose oxidase (GOD) is a typical fl avin enzyme with fl avin adenine dinucleotide
(FAD) as redox prosthetic group. Its biological function is to catalyze glucose to form
gluconolaction, while the enzyme itself is turned from GOD(FAD) to GOD(FADH
2
).
GOD was used to prepare biosensors in extensive fi elds. Many materials that can be
used to immobilize other proteins can be suitable for GOD. GOD adsorbed on CdS
nanoparticles maintained its bioactivity and structure, and could electrocatalyze
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