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Measuring conductivity of living Geobacter sulfurreducens biofilms.
| Content Provider | Semantic Scholar |
|---|---|
| Author | Yates, Matthew D. Strycharz-Glaven, Sarah M. Golden, Joel P. Roy, Jared Tsoi, Stanislav D. Erickson, Jeffrey S. El-Naggar, M. Barton, Scott Calabrese Tender, Leonard M. |
| Copyright Year | 2016 |
| Abstract | To the Editor — Certain microorganisms can use an electrode as a metabolic electron acceptor or donor by means of extracellular electron transport (EET) processes1,2. Such microorganisms are studied as potential catalysts for electrode reactions such as the electrosynthesis of fuel precursors from reduction of CO2 using renewable sources of electricity3. The appeal of microbial electrode catalysts is that they self-assemble and self-heal, and the prospect of optimizing their catalytic properties (for example, reaction product and yield) through molecular engineering. In addition to enabling electron transport across a microbial/electrode interface, EET processes can often facilitate long-distance electron transport, resulting in the formation of multi-cell-thick electrode-grown biofilms, which are electrically conductive and can exceed 100 μm thickness. Such biofilms challenge the notion that biological electron transport is limited to molecular length scales. The fundamental mechanism of EET underlying biofilm conductivity has implications across many disciplines and is yet unresolved. Malvankar et al. reported that living electrode-grown biofilms comprising Geobacter sulfurreducens, a well-studied long-distance EET-capable microorganism, possess metallic-like conductivity similar to that of organic semiconductors4, a property that would make these biofilms unique among all biological materials. Electrochemical gating measurements were performed in a manner similar to that used to study conducting polymer films in electrolytic solutions5. Based on the resulting conductivity versus gate potential response, the authors proposed that living electrodegrown G. sulfurreducens biofilms are metallic-like conductors. When performing our own electrical electrochemical gating measurements of living electrode-grown G. sulfurreducens biofilms, we obtained a distinctly different conductivity versus gate potential response — one consistent with redox conductivity, similar to that of redox polymers6 and not consistent with metalliclike conductivity (Fig. 1 and Supplementary Fig. 1)5. Furthermore, it was recently demonstrated that conductivity of living electrode-grown G. sulfurreducens biofilms decreases with decreasing temperature in a manner that is also consistent with redox conductivity and not with metallic-like conductivity1. And it was also recently demonstrated that conductivity of these biofilms examined in air increases with decreasing temperature when the ambient water content is kept constant, and decreases with decreasing temperature when the ambient relative humidity is kept constant2. Again, both dependencies are consistent with redox conductivity and not with metallic-like conductivity2. Redox conductivity is ubiquitous in biological systems at molecular length scales, but is without precedence for distances over which electron transport appears to occur through electrode-grown G. sulfurreducens biofilms. The different conductivity versus gate potential response we obtained for living electrode-grown G. sulfurreducens biofilms prompted us to undertake a direct comparison of electrochemical gating measurements performed using our methods and measurements we replicated using the methods of Malvankar and colleagues. In this comparison, electrochemical gating measurements were performed on living G. sulfurreducens biofilms (Fig. 1 and Supplementary Fig. 1) as well as on two well-known conducting polymers: electropolymerized polyaniline, a known organic semiconductor5 (referred to here as PANI) (Fig. 2 and Supplementary Fig. 2); and poly(Nvinylimidazole [Os(bipyridine)2Cl]), a known redox conductor7 (referred to here as PVI-Os(bipy)2Cl) (Fig. 2 and Supplementary Fig. 3). Following Malvankar and colleagues’ approach, our biofilm electrochemical gating measurements were performed under physiologically relevant conditions in an aqueous electrolyte medium using gold source and drain electrodes patterned on a glass surface. Biofilms were grown that extended across the gap separating the electrodes, electrically connecting the source and drain. Different potentials were applied to the electrodes (ES and ED), generating a source–drain current (ISD) through the biofilm between the electrodes. In the limit of sufficiently small source–drain voltage, VSD = ED – ES ≤ 0.05 V (ref. 1), Ohm’s law applies such that: |
| Starting Page | 910 |
| Ending Page | 913 |
| Page Count | 4 |
| File Format | PDF HTM / HTML |
| DOI | 10.1038/nnano.2016.186 |
| PubMed reference number | 27821847 |
| Journal | Medline |
| Volume Number | 11 |
| Issue Number | 11 |
| Alternate Webpage(s) | https://frontis-energy.com/wp-content/uploads/2018/05/electron_transfer/Yates_Malvankar_repetition_NatNano.2016.pdf |
| Alternate Webpage(s) | https://doi.org/10.1038/nnano.2016.186 |
| Journal | Nature nanotechnology |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
