Contrast and resolution from biological objects examined in the electron microscope with particular reference to negatively stained specimens

SUMMARY For the practical biologist applying electron microscopy to the study of biological macromolecules, there are serious problems in obtaining high resolution images showing detail below 2.5–3.0 nm. The limitation in resolution from biological specimens can be attributed to support film thickness and granularity, specimen preparation, irradiation damage, focusing effects and possible contamination in the electron beam. Specimens possessing repeating features can be analysed and averaged by optical diffraction and image reconstruction methods which offer some improvement to the signal to noise ratio. The above problems, with particular reference to irradiation damage, still impose the basic limitation for high resolution applications. When considered together they offer formidable difficulties in practical terms in attempting to make full use of the potential resolving power of modern electron microscopes.