Nanoscale deformation in polymers revealed by single-molecule super-resolution localizationorientation microscopy
Muzhou Wang, James M. Marr, Marcelo I. Davanco, Jeffrey W. Gilman, James A. Liddle
Single-molecule super-resolution microscopy has attracted interest in materials science because of its ability to non-invasively explore nanostructures in real-space, but it also introduces a new set of challenges, including the need to image dense periodic structures, and an increased dependence of localization accuracy and resolution on fluorophore orientation. In this study, we optically image nanolithographically patterned polymer films in order to demonstrate the capabilities of this technique on model structures that are more representative of typical situations in materials science. Using simple labeling procedures and standard optical configurations, we can clearly resolve periodic features of 20 nm half-pitch, and individual features 25 nm 25 nm. Electron microscopy provides a ground truth for direct comparison with the optical images, enabling direct measurement of fluorophore localization error that includes both precision and accuracy. We use this error to derive a general expression for resolution based on a simple statistical argument. Finally, we also determine fluorophore orientation simultaneously with position by comparing their point-spread functions to vectorial diffraction calculations. Although orientation has been identified as a source of localization error, we demonstrate that it can also report changes to the nanoscale environment in films patterned by nanoimprint lithography. By combining super-resolution imaging with orientation for the first time, we can directly detect areas of local nanoscale deformation.