Biomedical Engineering Reference
In-Depth Information
product NADH can reduce Med to its reduction state Med
red
. If Med is modifi ed on an electrode,
Med
red
will be oxidized to Med
ox
, and an electric signal is observed [76] (Figure 14.2a). Similar
results can be achieved in the reaction of pyruvate to lactate as shown in Figure 14.2b.
Based on the above mechanism, amperometric biosensor for the detection of lactate (or NAD
+
)
can be formed by immobilizing NAD
+
(or lactate), LDH, and Med on electrodes. In contrast,
amperometric biosensor for the detection of pyruvate (or NADH) can be prepared by immobilizing
NADH (or pyruvate), LDH, and Med on electrodes. Some examples can be found in Table 14.7.
14.1.1.6 Pyruvate Oxidase
Pyruvate oxidase (PyOD, E.C. 1.2.3.3) was fi rst found in
Escherichia coli
by Hager [81] in 1957. PyOD
is a tetramer consisting of four similar subunits; each subunit combines a molecule of FAD tightly.
Med
ox
Pyruvate
e
−
NADH
LDH
Med
red
NAD
+
Lactate
Electrode
(a)
Med
red
NAD
+
Lactate
e
−
LDH
Med
ox
Pyruvate
NADH
Electrode
(b)
FIGURE 14.2
Induction of electron transferring during the reaction of lactate to pyruvate (a) and the reverse
reaction of pyruvate to lactate (b) in the presence of Med. (Modifi ed from Catherine, M., Simon, E., Toh, C.S.,
Bartlett, P.N., and Cass, A.E.G.,
Anal. Chim. Acta.
, 453, 191, 2002. With permission.)
TABLE 14.7
Examples of Amperometric Biosensors Prepared by LDH
Substrates
Mediators
Signal Transducers
Immobilization Method of Enzyme
Ref.
Lactate
Toluidine blue O moiety
Carbon-paste
electrode
LDH was immobilized with NAD
+
on
redox polymer and polyethylenimine
77
NAD
+
Poly(3-ethylthiophene)/
poly(phenol red)
Pt electrode
LDH was immobilized with lactate on
the poly(3-methylthiophene)/
poly(phenol red) membrane
78
Pyruvate
Electrochemically
prepared PANI fi lm
ITO glass plate
electrode
LDH was immobilized with NADH on
the PANI fi lm
79
NADH
A thiol-terminated,
sol-gel-derived, 3-D,
silicate network
Polycrystalline Au
electrode
LDH was immobilized on the Med
with Au nanoparticles (NPs)
80
