Interfacial electron transfer between Geobacter sulfurreducens and gold electrodes via carboxylate-alkanethiol linkers: Effects of the linker length

Geobacter sulfurreducens (Gs) attachment and biofilm formation on self-assembled monolayers (SAMs) of carboxyl-terminated alkanethiol linkers with varied chain length on gold (Au) was investigated by electrochemical and microscopic methods to elucidate the effect of the surface modification on the current production efficiency of Gs cells and biofilms. At the initial stage of the cell attachment, the electrochemical activity of Gs cells at a submonolayer coverage on the SAM-Au surface was independent of the linker length. Subsequently, multiple potential cyclings indicated that longer linkers provided more biocompatible conditions for Gs cells than shorter ones. For Gs biofilms, on the other hand, the turnover current decreased exponentially with the linker length. During the biofilm formation, bacteria need to adjust from the initial planktonic state to an electrode-respiring state, which was triggered by a strong electrochemical stress found for shorter linkers, resulting in the formation of mature biofilms. Our results suggest that the initial cell attachment and the biofilm formation are two inherently different processes. Therefore, the effects of linker molecules, electron transfer efficiency and biocompatibility, must be explored simultaneously to understand both processes to increase the current production of electrogenic microorganisms in microbial fuel cells.