Using the dynamics of fluorescent cations to probe and map charged surfaces

We present a new quantitative imaging method, based on accumulated single molecule trajectories, to map and probe surface charge heterogeneity. Using a fluorescent cation as a probe molecule, we found that surface charge has a dramatic affect on the local adsorption rate, primarily through its influence on near-surface ion concentrations. Other physical measures, including surface residence time and diffusion coefficient, provided complementary information about the probe-surface interaction that can be obtained only through a single molecule approach. We present spatial maps of surface charge based on each of these dynamic probe properties. Spatial maps of adsorption rate constant, surface residence time and surface diffusion coefficient based on accumulated single molecule trajectories at a heterogeneously charged surface.