Determining Atomic Structures from Digitally Defined Regions of Nanocrystals
Presented by Marcus Gallagher-Jones, postdoc, Jose Rodriguez group, UCLA
The ability of molecules to form ordered assemblies is a crucial first step in preparing samples for structural characterization with atomic-level detail. For many complex molecules, the length scales to which this order extends is limited, thus hampering efforts to solve their structures. In our current work we attempt to overcome these challenges by extending recent developments in 4D-STEM. By combining 4D-STEM data collection with tomography we demonstrate that atomic structures of macromolecules can be solved from specific regions of polymer nanocrystals. In this method, scanning nanobeam electron diffraction tomography (nanoEDT), peptide nanocrystals are rotated about a tilt axis in one-degree steps. At each tilt angle a direct electron detector captures thousands of sparse diffraction patterns mapped to specific locations within a single crystal. The use of direct electron detection, in combination with data collection at cryogenic temperatures and a hybrid counting algorithm, allows even weak signals from high-resolution Bragg peaks to be accurately recorded from radiation sensitive crystals. NanoEDT breaks new ground in nanocrystallography by allowing atomic structures to be determined from any region of a nanocrystal through the use of virtual, selected-area apertures, potentially leading to the determination of atomic structures from heterogeneous or polycrystalline nanoassemblies.
High resolution imaging through scattering media
Presented by Sakshi Singh & Evolene Premillieu, graduate students, Rafael Piestun group, CU Boulder
Imaging through scattering media is a critical area with impact in biological and biomedical research. While most current research focuses on achieving the highest possible resolution, in practice, scattering is often the main limitation. Scattering diffuses light, leading to a reduction in contrast and signal-to-noise ratio, which makes imaging impractical. The implications of this study span all imaging modalities from visible light to electron beam. One approach to deal with scattering involves characterizing the medium by measuring its transmission Matrix (TM). Once the TM is acquired, imaging and focusing inside the medium become feasible. Here we present two critical advances in this field. The first involves TM measurement using fluorescence (namely incoherent light) as feedback, allowing to focus light on an extended field of view behind a scatterer. Secondly, we demonstrate a huge step up in the imaging speed with the help of a grating light valve (GLV) that enables rapid and continuous focusing through scattering media at a record speed.