Biology Reference
In-Depth Information
An important hurdle to overcome in the development of MFC array systems is
the identifi cation of an electrode material that is durable, conductive, biocompat-
ible, and easily fabricated [33]. Graphite, in the form of carbon cloth or graph-
ite felt, has typically been the material of choice for the construction of MFC
anodes, and conductive elements such as manganese, iron, quinines, and neutral
red have been incorporated in graphite electrodes to signifi cantly increase power
output [33, 34]. However, graphite is not suitable for microfabricated MFC array
systems [35]. The surfaces of graphite electrodes are non-uniform and diffi cult
to pattern in small-scale devices. This non-uniformity thwarts efforts to compare
performances between individual miniaturized MFCs. In addition, graphite mate-
rials are not compatible with most microfabrication technologies. Recently, gold
has been identifi ed as a potential material for MFC anode development [35]. Gold
is highly conductive, can be vapor deposited, and is compatible with a wide array
of conventional microfabrication modalities [36]. Thus, gold is a very attractive
anode candidate for the development of an MFC screening platform. Our result
showed that the MFC using gold as the anode material gave more reproducible
results than its carbon cloth counterpart, a critical feature for side-by-side com-
parison in the MFC array. We therefore used gold as the anode material to develop
the MFC array prototype.
Biofi lms, when established on the anode of MFCs, enhance MFC performance
when some microbial systems (including
S. oneidensis
MR-1) are employed. The en-
hanced performance has been suggested to result from the enhanced ability of biofi lms
to exploit close physical contacts between microbial membranes and the anode surface
for electron transfer [11]. To investigate whether biofi lms form on the surface of gold
electrodes, light and fl uorescence microscopy images of the electrode were captured 1
hr and 5 hr post-inoculation (PI). One hour PI, microbes started attaching to the gold
electrode surface. Five hours later, an attached
S. oneidensis
biofi lm was observed.
Scanning electron micrographs of the electrode surface confi rmed microbial attach-
ment. Therefore, gold electrode supports
S. oneidensis
biofi lm formation, and more-
over, enables reproducible and consistent electrochemical activity to be measured
when this model organism is used.
We were encouraged by our fi nding that gold electrodes can be employed in MFC
devices, and exploited this material to develop an MFC array (Figure 2A). The array
was successfully microfabricated using micromachining and soft lithography tech-
niques. Performance and reproducibility of the MFC array were initially assessed by
loading
S. oneidensis
MR-1 into the device and then measuring the electrical output.
The current densities for negative control (un-inoculated medium) and
S. oneidensis
MR-1 chambers were 0.40 ± 0.01 mA/m
2
(mean ± SE, n = 4) and 1.80 ± 0.24 mA/m
2
(mean ± SE, n = 4), respectively (Figure 3A). Therefore the MFC array reproducibly
measured the electrochemical activities of this microbial system (less than 14% of
variance).
