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Tunable metallic-like conductivity in microbial nanowire networks

Abstract

Electronic nanostructures made from natural amino acids are attractive because of their relatively low cost, facile processing and absence of toxicity1,2,3. However, most materials derived from natural amino acids are electronically insulating1,2,3,4,5,6. Here, we report metallic-like conductivity in films of the bacterium Geobacter sulfurreducens7 and also in pilin nanofilaments (known as microbial nanowires8,9) extracted from these bacteria. These materials have electronic conductivities of 5 mS cm−1, which are comparable to those of synthetic metallic nanostructures2. They can also conduct over distances on the centimetre scale, which is thousands of times the size of a bacterium. Moreover, the conductivity of the biofilm can be tuned by regulating gene expression, and also by varying the gate voltage in a transistor configuration. The conductivity of the nanofilaments has a temperature dependence similar to that of a disordered metal, and the conductivity could be increased by processing.

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Figure 1: Strategy to measure in situ biofilm conductivity.
Figure 2: Measurement setup and conductance data.
Figure 3: Evidence for pili being associated with biofilm conductivity.
Figure 4: Observation of metallic-like nature of conductivity.

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Acknowledgements

The authors thank D. Venkataraman, C. Salthouse, M. Aklujkar, J. Nicholson, R. Krotvov, A. Ursache, O. Yavuzcetin and S. Ebru Yalcin for helpful discussions and technical assistance. This research was supported by the Office of Naval Research (grant no. N00014-10-1-0084), the Office of Science (BER), US Department of Energy (award no. DE-SC0004114 and Cooperative Agreement no. DE-FC02-02ER63446 as well as the NSF Center for Hierarchical Manufacturing (grant no. CMMI-0531171)).

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Contributions

The experiments were designed by N.S.M., K.P.N. and M.T.T., with suggestions from A.E.F., S.F.C, V.M.T. and D.R.L. N.S.M. performed electrical measurements, X-ray studies and AFM imaging of pili preparations. M.V. prepared and TEM-imaged pilin filaments and performed haem staining. N.S.M., M.V., B.C.K., K.I. and T.M. performed protein measurements. B.C.K. generated the BEST strain. C.L. generated the CL-1 strain and performed the peeling and TEM-imaging of biofilms. A.E.F. and J.P.J. carried out the confocal imaging of biofilms. N.S.M., M.T.T. and D.R.L. analysed the data and wrote the manuscript. All authors discussed the results and commented on the manuscript.

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Correspondence to Mark T. Tuominen or Derek R. Lovley.

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Malvankar, N., Vargas, M., Nevin, K. et al. Tunable metallic-like conductivity in microbial nanowire networks. Nature Nanotech 6, 573–579 (2011). https://doi.org/10.1038/nnano.2011.119

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