Autoradiography of Gels Containing 32P

Autoradiography of gels containing a 32 P label is used to detect and quantitate the radioactive label in a particular band or spot. Since 32 P is a high energy β-emitting isotope, no fluor is required in the gel (as in fluorography) to increase the efficiency of detection. However, since most of the radiation of high energy emitters (e.g., 32 P or 125 I) passes through the film without being absorbed, it is common to employ an intensifying screen (e.g., calcium tungstate), where the radiation from the isotope is absorbed by a fluorescent compound that reemits the energy as light. The intensifying screen is placed against the film on the opposite side from the radioactive source. Any radiation that passes right through the film is then absorbed by the screen, where light is emitted back onto the film. In this way, much more of the emitted radiation is used and the film is exposed by a combination of direct and indirect autoradiography. The time needed to obtain an autoradiography is therefore reduced when an intensifying screen is used. If a small amount of label is present, it is also advisable to use an intensifying screen in the cassette to decrease the time of exposure required.