Detecting Iodine-Labeled Cells

Abstract

The binding of radiolabeled reagents to cells is detected by coating the specimen with a photographic emulsion. When the emulsion is developed, silver grains can be seen at the location of the radiolabel. The silver grains appear as black dots in bright-field microscopy but are most readily detected by dark-field illumination, in which they are seen as intense silver reflections on a black background. The detection of iodine-labeled reagents is extremely sensitive, and the reaction is readily controlled by setting up duplicate samples and varying the exposure time. The method is compatible with histological stains and can be used in double-labeling procedures with enzyme- or fluorochrome-labeled reagents. When iodine-labeled and enzyme-labeled reagents are used together for double labeling, the enzyme-labeled reagents must be developed before the photographic emulsion is added.