Conductive Polymers to ‘Wire’ the Microbial Electronics Interface

Abstract

Organic waste streams contain a significant amount of latent energy that is difficult to harvest. Microbial electrochemical systems (MESs), which extract electrons through microbial metabolism, are a promising technology to recover this energy. Despite advances in these technologies, microbial electrocatalysis in MESs remains limited by inefficient electron transfer between living cells and electrodes. Here, we demonstrate significant improvement in this interfacial electron transfer through the incorporation of electron- and ion-conductive polymers. We have designed these polymers with a conductive backbone and side chains that mimic ligands of catalytic centers in redox-active enzymes. Specifically, methylimidazolium groups mimic protonated histidines prevalent in enzyme active sites. We show that these polymers substantially enhance mediated electron transfer and overall current generation by Shewanella oneidensis, an electroactive microbe often used in MESs. Our work highlights the importance of materials engineering applied to the biotic-abiotic interface to improve charge transfer in bioelectronic systems.

Electrochemical Characterization of Biomolecular Electron Transfer at Conductive Polymer Interfaces

“…Biological implications of findings.-The two-electron transfer predicted by Levich analysis of P3HT-Im + is consistent with our prior work, in which two electrons were predicted to be transferred by fitting the Randles-Ševčík equation to cyclic voltammograms of varying scan rate. 52 While (to our knowledge) concerted twoelectron transfer at an electrode has not been previously reported for FMN, two-electron transfer to flavins is well established in enzymology. In proteins, the chemical environment of flavin cofactors often destabilizes the partially-reduced semiquinone form of FMN, resulting in exclusively two-electron transfers.…”

“…28 At low frequencies, P3HT exhibits a phase angle that significantly diverges from the ideal 90-degree angle. This behavior is attributed to high surface roughness, 52 which can lead to non-ideality due to heterogeneity in charge access to the double layer. 60 Both P3HT-Im + and the P3HT/P3HT-Im + copolymer exhibit a second arc separated from the high-frequency component but blended with the capacitor-like features observed at low frequencies (Figs.…”

“…Polymer coated electrode preparation.-P3HT-Im + homopolymer and 50:50 P3HT / P3HT-Im + copolymer were each synthesized as described previously. 52 For drop coating, P3HT homopolymer (Reike Metals, Lincoln, NE), P3HT-Im + Br -, and copolymer were dissolved to a final concentration of 40 mg ml -1 in chloroform, methanol, and 30:70 (v/v) dimethylformamide in methanol, respectively. The solutions were then drop coated via micropipette onto screen-printed carbon electrodes (SPCEs, Pine Research Instrumentation, Durham, NC) or glassy carbon electrodes (GCEs, Part # AFED050P040GC, Pine Research).…”