Biomedical Engineering Reference
In-Depth Information
The cell was studied for 48 hours in a fl ow system under constant glucose concentra-
tion (1 mM) under air and showed no sign of current or cell potential decrease.
A biocatalytic fuel cell reported by Tsujimura
et al.
[87] is based on polished
glassy carbon electrodes modifi ed by
Mv
BOD for the anode and PQQ-GDH from
Acenitobacter calcoaceticus
for the cathode. Redox mediation is effected by [Os(2,2
-
bipyridine)
2
Cl]
conjugated to poly(4-vinylpyridine) quaternized with bromoethyl-
amine (redox potential of 0.35 V vs Ag/AgCl) for the cathode, while the anode
contains [Os(4,4
-bipyridine)
2
Cl]
conjugated to poly(vinylimidazole)
-dimethyl-2,2
(redox potential of
0.15 V vs Ag/AgCl). The cell, assembled and studied in MOPS
buffer, pH 7, containing 3 mM CaCl
2
, yielded an open circuit voltage of 0.44 V (25ºC),
with maximum current density of 430
Acm
2
and maximum power density of
µ
Wcm
2
at a cell potential of 0.19 V. The cathode was identifi ed as limiting the cell
performance, as a three times lower current density than the anode was obtained under
the same conditions. The advantage of using the GDH enzyme at the anode rather than
GOx, in addition to insensitivity to O
2
, is that GDH is more tolerant to redox media-
tors of redox potential close to that of the enzyme. Indeed, the authors showed that
despite a higher
E
0
(
58
µ
0.35 V for GOx at pH 7) the bio-anode
modifi ed with GDH and the 0.15 V redox polymer yielded more than twice the current
density than that modifi ed with GOx and the same redox polymer. Finally GDH is less
substrate selective than GOx. This is a drawback for glucose determination but may be
an advantage for some fuel cell applications. The fuel cell stability was not reported
but the need to stabilize the GDH enzyme was stressed.
Recently, Yuhashi
et al.
[84] attempted to address the GDH instability by using a
mutated GDH (Ser415Cys). Their glucose-O
2
glucose dehydrogenase/bilirubin oxi-
dase biocatalytic fuel cell was studied in a two-compartment cell linked by a salt
bridge and containing ABTS and phenazine methosulfonate (PMS) redox mediators
in the cathode and anode compartment, respectively. The electrodes were made by
packing a lyophilized mixture of the enzyme and carbon paste at the surface of a car-
bon electrode, followed by treatment by a 1% glutaradehyde solution. The anode was
allowed to undergo holoformation in a solution containing CaCl
2
(1 mM) and PQQ
(5
0.18 V for GDH and
M) before use. The open circuit voltage of the cell was 0.577 V (25ºC, pH 7). The
maximum current density was 61.4
µ
Acm
2
under stirring (250 rpm) and the maxi-
µ
Wcm
2
at a cell potential of 0.5 V with an external load
mum power density was 17.6
µ
of 200 k
. The half-life of the cell was under a week, while that of the wild type GDH
was only 2 days. The eventual inactivation of the cell is ascribed to mediator insta-
bility. Sato
et al.
[89] used an NAD
-dependent GDH anode that was coupled to a
platinum cathode, not modifi ed by any bio-catalyst, in their fuel cell. Diaphorase from
Bacillus stearothermophilus
, was co-immobilized with polyallylamine functionalized
with a derivative of vitamin K
3
as the redox mediator to yield an NADH oxidation
layer. A second layer of an electrostatic adducts between GDH and polylysine effected
glucose oxidation. Crucial to the effi cient electrical conduction between the vitamin
K
3
mediator and the electrode was the addition of carbon black in the diaphorase layer.
Indeed the current density was two orders of magnitude higher in the presence of the
conducting material. The “double-layer” design of the anode implies that the optimized
Ω
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