Nanowires, Capacitors, and Other Novel Outer-Surface Components Involved in Electron Transfer to Fe(III) Oxides in Geobacter Species

In the first 8 months of this grant we initiated investigations on several of the new hypothesis in the proposal. Hypothesis 1-4 deal with the mechanisms of conductivity along the length of the pili of Geobacter sulfurreducens. The initial approach to evaluating these mechanisms was to attempt to measure end-to-end conductivity of the pili with lithographically-patterned electrodes in which conductive strips of graphite are placed on an insulating silicon dioxide surface. To our knowledge this is the first time that such conductivity measurements have been attempted with natural protein structures. Conductivity along the pili was measured with two methods. In the first method, the conductivity of the pili was measured by applying a voltage between the lithographic electrodes. In the second method, the voltage was applied between one lithographic electrode and the AFM tip. To date, we have not been able to consistently measure current of pili because of an inability to readily observe pili on the nanoelectrode system. Although we were able to make conductivity measurements in this manner on one attempt, we have not been able to consistently obtain appropriate preparations to consistently make such measurements. Therefore, we are evaluating strategies to modify this approach to make it more consistent