Electron holographic observation for biological specimens: Electron holography of bio-specimens

Electron holography has been applied to the observation of biological filaments. The technique has some advantages over conventional imaging for observing weak-phase objects such as small unstained biological structures. To avoid artificial structural transformation of the sample owing to the interaction with the supporting film, a holey carbon film was used to support the filaments. A tobacco mosaic virus bridged over a hole was observed as a cylindrical shape: the contrast distribution across the filament represents its actual shape, which is difficult to obtain with conventional transmission electron microscopy. A number of technical limitations which at present prevent high-resolution structure analysis of biological macromolecules by electron holography are discussed in this report.