Biology Reference
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wells were embedded. Each microliter-scale microbe culture well was combined with
individually addressable anode and cathode electrodes and functioned as a separate
MFC. The layers included anode electrodes, anaerobic microbe culture chambers (an-
ode wells), a PEM, cathode chambers, and cathode electrodes (Figure 2A). The as-
sembled device (Figure 2B-E) with acrylic supporting frames was coupled to a load
resistor circuit board and a digital multimeter through a computer controlled switch
box module and a data acquisition system (Figure 2F).
Twenty-four Well MFC Array Electrode Layer Microfabrication
An acrylic master mold having 4 × 6 arrays of pillars (diameter: 7 mm, height: 4 mm)
was fabricated with a rapid prototyping machine (MDX-40, Roland Inc., Los Angeles,
CA). PDMS precursor solution (Sylgard 184, Dow Corning, Auburn, MI) prepared by
mixing base and curing agent at 10:1 ratio (v/v) was poured onto the acrylic master
mold. After curing for 30 min at 85°C, the resulting polymerized polydimeyhylsi-
loxane (PDMS) slab was peeled off, creating an inverse replica of the acrylic mas-
ter mold. The cathode layer was prepared by aligning and permanently bonding a
PDMS well layer onto a patterned electrode layer. Platinum loaded carbon cloth (10%,
A1STD ECC, BASF Fuel Cell, Inc., Somerset, NJ) was cut to the size of a well (diam-
eter: 7 mm) and bonded on top of the Au electrode pads in the cathode electrode layer
using silver paste (Structure probe, Inc., West Chester, PA). Cathode and anode elec-
trode layers of the 24-well MFC array were fabricated using standard microfabrication
techniques. The fabricated cathode and anode electrode substrates had 24 individually
addressable electrodes, each having an 8 mm diameter disk pattern. Wires were then
soldered to all contact pads to provide electrical interconnects between the MFC ar-
rays and the voltage measurement setup.
Assembly of the MFC Array System
The 24-well MFC array system consisted of a 24-cathode array layer, a cathode well
layer, a PEM, an anode well layer, and a 24-anode array layer. Cathode layer consisted
of a PDMS well layer permanently bonded on an electrode layer. Platinum (Pt) loaded
carbon cloth was cut to the size of the well (diameter: 7 mm) and bonded on top of
the Au electrode pads. The anode layer consisted of three layers: two PDMS layers
fabricated as described above and an acrylic layer (8 mm thick) having 4 × 6 arrays of
through-holes (7 mm diameter) fabricated by a rapid prototyping machine. The two
PDMS layers were placed on both sides of the acrylic layer. The rigid acrylic layer
served as a support layer that could be clamped tightly in the subsequent assembly
step. The cathode layer, activated PEM, and the anode layer were then assembled to-
gether. To assemble these layers together, a top and bottom acrylic support frame that
could be used to tightly clamp all layers together in between was cut out using a rapid
prototyping machine. The sequence of images (Figure 2B-F) shows how all parts of a
24-well MFC array system was assembled.
Organisms, Media and, Growth Conditions
Shewanella oneidensis MR-1 was obtained from American Type Culture Collection
(ATCC, Manassas, VA). Environmental bacteria used for screening were isolated from
 
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