Topological polymers such as ring polymers often display unexpected static and dynamic behaviors, and thus could contribute to the development of new polymer materials through a topology-directed control of the rheological properties. In contrast to linear polymers whose chain dynamics have been experimentally and theoretically well characterized at the molecular level, the diffusion and relaxation of cyclic polymers under entangled conditions that play a critical role in their rheological properties remain elusive. Thus, molecular level characterization of diffusion and relaxation of polymers would contribute greatly to understanding the rheological properties of topological polymers at the most fundamental level. However, conventional methods (e.g. single-molecule localization and tracking) cannot provide information about molecular diffusion and its conformational relaxation simultaneously.<br/>Here we report new single-molecule methods that allow for the characterization of diffusion and relaxation of semiflexible polymers under entangled conditions using fluorescently-labeled linear and cyclic DNA as model systems. We first developed a new single-molecule tracking method that enables simultaneous quantitative characterization of diffusion rates, modes, and conformational relaxation of polymer chains by analyzing areas occupied by diffusing molecules. Using this method, we demonstrated experimentally for the first time the decoupling of diffusion and relaxation and the critical role played by mutual relaxation in the cyclic polymers. We further developed single-molecule tracking method that quantifies molecular motion by the probability that the molecule visits new sites, which can capture hidden nonrandom diffusional motion of polymer molecules that cannot be detected by other tracking methods. We also report time-lapse super-resolution fluorescence microscopy technique that can directly visualize local chain dynamics (i.e., relaxation) together with lateral motion of the entire molecule (i.e., diffusion).

Single-molecule characterization of topological polymer dynamics

255th National Meeting (2018)

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