  We tested the enhancement of electrical current generated from
photosynthetically active bacteria by use of electrodes with porosity on the
nano- and micrometer length-scale. For two cyanobacteria on structured
indium-tin-oxide electrodes, current generation was increased by two orders of
magnitude and the photo-response was substantially faster compared to
non-porous anodes. These properties highlight porosity as an important design
strategy for electrochemical bio-interfaces. The role of porosity on different
length scales was studied systematically which revealed that the main
performance enhancement was caused by the increased surface area of the
electrodes. More complex microstructured architectures which spanned biofilms
as translucent 3D scaffolds provided additional advantage in the presence of
microbial direct electron transfer (DET). The absence of a clear DET
contribution in both studied cyanobacteria, Synechocystis and Nostoc, raises
questions about the role of conductive cellular components previously found in
both organisms.
