Wire-Loop Application of Liquid Emulsion to Slides for Autoradiography in Light Microscopy

This is an adaptation of procedures used to prepare autoradiographs for electron microscopy to light microscopy. A rectangular wire loop slightly larger than the slide is used. The liquid emulsion is prepared by mixing 1 volume of a 0.1% solution of Dreft or Ivory Snow with 2 volumes of Kodak NTB3 nuclear track emulsion. The slide to be coated is placed on a cork stopper supported by a glass plate 61 cm from the safelight. The loop was withdrawn from the liquid emulsion, with the plane of the loop parallel to the surface of the liquid, placed directly over the slide and slowly lowered so that the film (in the sol state) was broken by the slide. If desired, the film can be allowed to gel before application to the slide by waiting approximately 40 sec after the loop is removed from the liquid emulsion. That the developed emulsion is consistently uniform was indicated by a thickness of 0.4 ± 0.02 μm. Diluted emulsion can be stored after use for 1-2 wk at 2-8 C and used a second time before discarding. The identification of human D group chromosomes labeled with tritiated thymidine as well as prescreening patients for the Lesch-Nyhan syndrome, which utilizes tritiated hypoxanthine labeling, have been successfully carried out by applying the emulsion in the sol state.