Ion Depletion in the Interfacial Microenvironment from Cell-Surface Interactions.

The nanoscale region immediately adjacent to surfaces, although challenging to probe, is directly responsible for local chemical and physical interactions between a material and its surroundings. Cell-surface contacts are mediated by a combination of electrostatic and acid-base interactions that alter the local environment over time. In this study, a label-free vibrational probe with a nanometer length scale reveals that the electrostatic potential at a silica surface gradually increases in the presence of bacteria in solution. We illustrate that the cells themselves are not responsible for this effect. Rather, they alter the interfacial chemical environment in a manner that is consistent with a reduction of the ionic strength to a level that is roughly four times lower than that of the bulk aqueous phase.