An in‐vivo study of electrical charge distribution on the bacterial cell wall by Atomic Force Microscopy in vibratingforce mode.

Accepted for Publication in "Nanoscale": http://pubs.rsc.org/en/journals/journalissues/nr#!recentarticles&allWe report an in‐vivo electromechanical Atomic Force Microscopy (AFM) study of charge distribution on the cell wallof Gram+ Rhodococcus wratislaviensis bacteria, naturally adherent to a glass substrate, in physiological conditions.The method presented in this paper relies on a detailed study of AFM approach/retract curves giving the variation ofthe interaction force versus distance between tip and sample. In addition to classical height and mechanical (asstiffness) data, mapping of local electrical properties, as bacterial surface charge, was proved to be feasible at aspatial resolution better than few tens of nanometers. This innovative method relies on the measurement of thecantilever’s surface stress through its deflection far from (>10nm) the repulsive contact zone: the variations ofsurface stress come from modification of electrical surface charge of the cantilever (as in classical electrocapillarymeasurements) likely stemming from its charging during contact of both tip and sample electrical double layers.This method offers an important improvement in local electrical and electrochemical measurements at thesolid/liquid interface particularly in high‐molarity electrolytes when compared to technics focused on the direct useof electrostatic force. It thus opens a new way to directly investigate in‐situ biological electrical surface processesinvolved in numerous practical and fundamental problems as bacterial adhesion, biofilm formation, microbial fuelcell, etc