Direct Single-Electron Imaging using a pnCCD Detector

Abstract

Cryo-electron microscopy and especially cryo-electron tomography are widely applicable for structural studies in biology, but the major limitation is the extreme sensitivity of frozen hydrated biological samples to electron radiation [1–3]. Thus low-dose techniques have to be used, distributing the total electron dose (typically in the range of 50 electrons/Angstrom) to many single images, demanding highly sensitive recording devices. Phosphor-coated fiber coupled CCD cameras are typically used where the primary electrons are converted to visible light. This indirect detection strategy is characterized by significant levels of readout and dark current noise and the number of optical interfaces within the complete camera assembly results in multiple scattering and a subsequent loss in resolution. Since the total applied dose can’t be increased in cryo-EM studies, the improvement in camera performance with noiseless recording, a higher sensitivity and at the same time higher spatial resolution is therefore be definitely beneficial for low-dose cryo-applications [4,5].