PEDOT:PSS-based Multilayer Bacterial-Composite Films for Bioelectronics

Tom J Zajdel,Caroline M Ajo-Franklin,Moshe Baruch,Eleni Stavrinidou,Daniel T Simon,Gábor Méhes,Michel M Maharbiz,Magnus Berggren

doi:10.1038/s41598-018-33521-9

Abstract

Microbial electrochemical systems provide an environmentally-friendly means of energy conversion between chemical and electrical forms, with applications in wastewater treatment, bioelectronics, and biosensing. However, a major challenge to further development, miniaturization, and deployment of bioelectronics and biosensors is the limited thickness of biofilms, necessitating large anodes to achieve sufficient signal-to-noise ratios. Here we demonstrate a method for embedding an electroactive bacterium, Shewanella oneidensis MR-1, inside a conductive three-dimensional poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) matrix electropolymerized on a carbon felt substrate, which we call a multilayer conductive bacterial-composite film (MCBF). By mixing the bacteria with the PEDOT:PSS precursor in a flow-through method, we maintain over 90% viability of S. oneidensis during encapsulation. Microscopic analysis of the MCBFs reveal a tightly interleaved structure of bacteria and conductive PEDOT:PSS up to 80 µm thick. Electrochemical experiments indicate S. oneidensis in MCBFs can perform both direct and riboflavin-mediated electron transfer to PEDOT:PSS. When used in bioelectrochemical reactors, the MCBFs produce 20 times more steady-state current than native biofilms grown on unmodified carbon felt. This versatile approach to control the thickness of bacterial composite films and increase their current output has immediate applications in microbial electrochemical systems, including field-deployable environmental sensing and direct integration of microorganisms into miniaturized organic electronics.

Highlights

Because the effective surface area of the anode limits the number of bacteria that make electrical contact, many modification approaches aim to maximize the surface area to volume ratio of anodes
To improve the volumetric current density produced by whole cell sensors, we sought to embed S. oneidensis into a three-dimensional matrix of PEDOT:PSS around carbon felt (CF) (Fig. 1a)
We have demonstrated a new method for encapsulating electroactive bacteria into dense, multilayer conductive bacterial-composite films (MCBFs) that produce a 20x higher current-per-volume ratio than a native biofilm at steady state operation

Summary

Introduction

Because the effective surface area of the anode limits the number of bacteria that make electrical contact, many modification approaches aim to maximize the surface area to volume ratio of anodes. Encapsulation of S. oneidensis by PPy has been recently demonstrated to enhance the electron transfer rate from bacteria to anodes while maintaining bacterial viability[17] These materials do not significantly increase the density of the thin biofilm naturally formed by S. oneidensis[18]. The resulting MCBFs show a 20-fold increase in steady state current production over unmodified CF anodes when used in standard MESs. The scalable anode fabrication process, improved electron transfer through a 3D conductive biomatrix, high viability, and the ability to use strains that do not form thick native biofilms demonstrate an important advance towards establishing advanced, field-deployable anode modifications for MESs, or direct integration of microorganisms into miniaturized organic electronic devices

Results

Discussion

Conclusion