Event

This talk will discuss the experimental investigations of “natural organic metals” -- nanowires produced from amino acids by a common soil bacteria, Geobacter sulfurreducens. These protein nanofilaments, pili, extend outside of the cell for long distances and tangle into a network. Electron conductivity is observed in bacterial biofilms, and also in networks of pili extracted from the bacteria. The networks of pili can transport electrons over centimeter-long distances, thousands of times the size of a bacterium, and exhibit electronic conductivities comparable to synthetic organic metal-like nanostructures. The temperature and gate-voltage dependence of the conductivity is similar to quasi-1D disordered synthetic organic metals. The conductivity can be modulated by an applied electrochemical gate voltage and can be doped using protons. Preliminary X-ray diffraction studies suggest the possibility of molecular pi-pi stacking in pili, but at this point the complete structure of the Geobacter pili is unknown.

The discovery of electron conductivity in natural proteins represents a shift in our understanding of electron transfer in biology and electronic properties of biomaterials and suggests intriguing possibilities for biologically-produced electronic materials. These nature-made nanostructured materials have been used to develop microbial fuel cells and supercapacitance comparable to those of synthetic supercapacitors. Recently we electric-field scanning microscopy to make quantitative measurements of electron flow at a single cell level under physiological conditions. Using this approach, we have directly observed the distribution of injected electrons along individual pili.