Permission given to use photo for AskNature. Geobacter produces pilin-like filaments that function as nanowires to transfer electrons outside the cell onto insoluble electron acceptors, such as iron minerals and possibly electrodes. The filaments, which are only 3-5 nanometers in width (more than 10,000 times finer than a human hair), can extend more than 20 micrometers in length (more than 10 times the length of the cell). Elucidation of this novel form of electron transfer provides insight into the mechanisms by which Geobacter can contribute to bioremediation of groundwater contaminated with organic and metal contaminants. The potential to biologically mass-produce fine, long conductive filaments may have applications in the development of nanoelectronic devices, sensors, and microbially based fuel cells.