Direct extracellular electron transfer from Escherichia coli through modified carbon nanoparticles

Abstract

Direct electron transfer (DET) from bacteria to the electrode is one of the key factors in developing microbial electrochemical technology. While extensive study has been made for exoelectrogens, DET for nonexoelectrogens has not been seriously taken. Here we report our preliminary results on DET in which Escherichia coli (E. coli) was chosen as a model nonexoelectrogen and carbon nanoparticles (CNPs) as an electron conduit connecting E. coli and the electrode. To improve accessibility of CNPs to the bacterium and the carbon electrode, CNPs were modified with 4-aminophenyl groups (4AP) and the carbon surface with carboxyl groups. Thus modified 4AP-CNPs were positively charged in neutral pH that induces electrostatic interaction both with the negatively charged cell surface and with the electrode. When glucose was used as a substrate, oxidation current was observed at -110 mV vs. Ag/AgCl, indicating that electrons generated from the glucose oxidation were captured by 4AP-CNPs and directly transferred to the electrode, which was confirmed under various conditions. It was found that oxidation current increased with glucose concentration and without E. coli, no oxidation was observed. This work shows DET is possible even from nonexoelectrogens and opens a possibility for utilizing those bacteria.