Phase contrast electron microscopy: development of thin-film phase plates and biological applications

摘要

Phase contrast transmission electron microscopy (TEM) based on thin-film phase plates has beenrndeveloped and applied to biological systems. Currently, development is focused on two techniques thatrnemploy two different types of phase plates. The first technique uses a Zernike phase plate, which isrnmade of a uniform amorphous carbon film that completely covers the aperture of an objective lens andrncan retard the phase of electron waves by p/2, except at the centre where a tiny hole is drilled. The otherrntechnique uses a Hilbert phase plate, which is made of an amorphous carbon film that is twice as thickrnas the Zernike phase plate, covers only half of the aperture and retards the electron wave phase by p. Byrncombining the power of efficient phase contrast detection with the accurate preservation achieved by arncryotechnique such as vitrification, macromolecular complexes and supermolecular structures insidernintact bacterial or eukaryotic cells may be visualized without staining. Phase contrast cryo-TEMhas thernpotential to bridge the gap between cellular and molecular biology in terms of high-resolutionrnvisualization. Examples using proteins, viruses, cyanobacteria and somatic cells are provided.