Autoradiography (Autoradiography in Electron Microscopy)

Autoradiography in Electron Microscopy is a method to observe a specific site of a biological specimen labeled with a substance containing a radioactive isotope. The method is implemented in the following procedure.
A substance containing a radioactive isotope is doped into a biological specimen for labeling specific tissues or cells. The biological specimen is thinned down to an ultrathin section and a photo-sensitive emulsion (silver halide suspension) is applied to the thin section. Silver halides in the vicinity of the labeled sites are exposed with β rays emitted from the radioactive isotope. When photo-developed, silver particles are segregated at the labeled sites. When the section is observed with a transmission electron microscope, the positions of the labeled tissues or cells can be identified from the localized silver particles.
In order to perform high-resolution observation of the sites of the labeled tissues or cells, tritium (which emits small energy β-rays) is often used as a radioactive isotope because tritium causes small silver segregates in the photosensitive emulsion.
An example of Autoradiography in Electron Microscopy: Thymidine containing radioactive tritium is applied to label the sites where cell divisions are active in a biological specimen. The labeled sites are revealed from the segregated silver particles by observing the electron microscope image of the specimen.

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