Helena Lozano,<\/em> Nanoscale bioelectrical characterization group<\/em><\/p>\n Some bacteria can exchange electrons with non-soluble electron acceptors, such as minerals. This phenomenon is called Extracellular Electron Transfer (EET) and it can be done through several mechanisms, especially through conductive bacterial nanowires.<\/p>\n The main objective of this thesis is the investigation of the polarization properties of electrochemically active bacteria and their appendages. Specifically, I have studied two types of bacteria, Shewanella oneidensis <\/em>MR-1 and cable bacteria. I have used the Electrostatic Force Microscopy (EFM), which measures the electrostatic force using a nanometric probe, combined with finite element simulations to obtain the polarization properties. The electrostatic force depends mainly on the geometry and dielectric constant of the probe-sample system.<\/p>\n First, I have developed a way to obtain the dimensions of objects avoiding physical contact with the sample by measuring the electrostatic force. I have tested this technique on silver nanowires and bacterial flagella, optimizing the EFM technique to nanowire-like biological samples at the nanoscale. Afterward, I have studied S. oneidensis <\/em>Outer Membrane Extensions (OMEs), responsible for the EET. I have obtained a low value of the dielectric constant (\u03b5OME<\/sub>=3.7\u00b10.7). However, considering that the conduction mechanism of such OMEs is through electron hopping, where electrons are localized, these results do not contradict the literature.<\/p>\n I have also studied the cable bacteria, especially the fibers that are along this filamentous bacterium. The dielectric constant of the fibers was \u03b5r<\/sub>=7\u00b11. This result is not compatible with the conductivity reported in the literature. Therefore, a core-shell model was proposed with a conductive core of h<\/em>~10\u201320nm.<\/p>\n