Ptychographic Single Particle Analysis for Biological Science

Abstract

Cryo-electron microscopy (cryo-EM), has attracted significant efforts to develop techniques for the high resolution three-dimensional structure characterization of biological samples in a close-to-native state at high resolution, including single particle analysis[1] and tilted tomography[2]. However, unstained biological samples embedded in thin vitreous ice are essentially pure phase objects that are extremely radiation sensitive[3], and consequently images of these have low signal-to-noise ratios[4] and low contrast[5,6]. To counter the latter, cryo-EM relies on the use of phase contrast imaging at high defocus to improve information transfer at low spatial frequencies at the expense of higher spatial frequencies[7]. Therefore, it is important to develop ways to improve resolution and contrast without damaging samples, including the use of direct electron detectors and novel phase plates[6]. However, the routine applications of phase plates are still somewhat restricted by signal attenuation at high frequencies, inconsistent fabrication, poor reliability and short working lifetimes due to electrostatic charging[8,9].