Polypyrrole Electrodes Show Strain-Specific Enhancement of Photocurrent from Cyanobacteria

Abstract

The discovery of extracellular electron conduits has spurred new applications in microbial electronics. Except for a limited number of exoelectrogens, most microbes are surrounded by insulating membranes that impair extracellular electron transfer. This study focuses on the fabrication of a conductive polypyrrole (PPy) coating for enhancing microbial charge extraction. The polymer deposition is characterized and optimized using a combination of potentiodynamic and potentiostatic measurements as well as scanning electron microscopy (SEM), energy dispersive X-Ray (EDX) analysis, and Raman spectroscopy. The electrodes are used to extract photosynthetic electrons from the cyanobacteria Synechocystis sp. PCC6803 (Synechocystis) and Synechococcus Elongatus PCC7942 (Elongatus). The PPy electrode shows a sixfold increase in extracted photocurrent for Synechocystis under unmediated conditions compared to bare graphite electrodes. This enhancement is attributed to the decreased resistance and increased electroactive surface area of the PPy electrode. By contrast, Elongatus shows no substantial difference in photocurrent between the PPy and bare electrodes. Compared to Synechocystis cells, the Elongatus cells show limited electrode adherence with weaker charge interactions. These findings lay the framework for designing customized polymer electrodes for strain-specific charge extraction.