Three dimensional structure determination of a core-shell nanoparticle by single particle 3D imaging at PAL-XFEL*

Single particle imaging is a novel x-ray imaging technique that utilizes the extremely high brilliance and spatial coherence of X-ray Free Electron Laser (XFEL) to capture the complete 3D structure of non-crystalline sample. It enables high-resolution 3D imaging of non-crystalline biological specimens without staining, fixation, and sectioning. We established a hard x-ray fixed-target coherent diffraction imaging set-up at PAL-XFEL NCI beamline and recorded 2D diffraction patterns from sphere core-shell nanoparticles with trisoctahedral gold core. We reconstructed 3D image with two different approaches. One is to reconstruct the 3D reciprocal volume from the 2D diffraction patterns via EMC algorithm, and acquire 3D structure from phasing of reciprocal volume. The other is construct the 2D images first by phasing the single 2D diffraction patterns, followed by 3D image reconstruction from the 2D image sets which is a common scheme in cryo-EM. Clear core-shell structure in nanoscale and heterogeneity was observed in the reconstruction. Detailed analysis and comparison of both reconstruction would be discussed.