Imaging and Engineering Polypeptoid Nanosheets with Atomic Scale Precision*

Imaging soft materials with atomic resolution using electron microscopy is challenging because soft materials are unstable under the electron beam, and techniques such as x-ray scattering or diffraction are not able to provide atomic resolution phase information in position space. Our experiments were conducted on crystalline nanosheets formed by self-assembly of amphiphilic polypeptoid molecules in water. Low-dose cryo-electron microscopy micrographs were obtained from frozen hydrated crystalline nanosheets. A combination of crystallographic and single particle methods, developed for cryo-electron microscopy of biological macromolecules, was used to obtain high resolution images of the crystals. Our approach is robust and enable direct visualization of the arrangement of bromine atoms in crystalline polypeptoid nanosheets. It also enables the engineering of polypeptoid nanostructures with atomic scale precision.