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.