Autoradiography in the Scanning Electron Microscope

Abstract

THE results of electron microscopic examination of the structure of solids often need to be supplemented by tracing the chemical processes leading to particular structural features. This can be achieved by using radioisotopes, the distribution of which in the specimen can be determined well by autoradiography. Liquier-Milward was the first to apply electron microscopic autoradiography to biological objects¹. In this method ultrathin sections labelled with radioisotopes were covered with a monolayer of silver halogenide crystals sensitive to radiation. After exposure and development, the distribution of the silver, as revealed on an electron micrograph, indicates the sites of the radioisotope atoms in the specimen. Many authors have contributed to the progress of this technique^2–5. Although the resolution of about 1000 Å in electron microscopic autoradiography with tritium is far lower than that in common electron microscopic experiments, ultrastructure research has been aided in important instances by electron microscopic autoradiography. Fig. 1 shows, for example, the distribution of a ³H-labelled sizing auxiliary in a cellulose fibre. The need to prepare ultrathin sections, however, is a disadvantage.