Enhanced autoradiographic detection of 32 P and 125 I using intensifying screens and hypersensitized film

This paper reports that autoradiographic sensitivity can be greatly increased for isotopes which emit y rays (e.g., ‘251) or high energy p particles (e.g., 32P) by placing a pre-exposed film between the sample and a calcium tungstate (CaW04) X-ray intensifying screen and exposing at --70°C. The combination of preexposed Kodak X-OMAT R film with either a Fuji Mach 2 screen or a Du Pont Lightning Plus screen at -70°C enhances detection efficiency 1 OS-fold for 32P and 16-fold for “‘1 when compared to conventional autoradiography on Kodirex film. The method is applicable to wet or dry gels, to chromatograms on paper or thin layer plates, or to nitrocellulose filters. Emissions from the sample pass through the film producing a direct autoradiographic image. Emissions which pass completely through and beyond the film are absorbed more efficiently by the screen where they produce multiple photons of visible light which return through the film superimposing a photographic image over the autoradiographic image. Although intensifying screens are used routinely in medical radiography [2] , their use for the much longer exposures used in biochemical autoradiography depends on by-passing the initial reversible stage of latent image formation [3]. As explained previously this problem can be overcome by lowering the temperature to -70°C [ 1,4] and hypersensitizing the film by pre-exposing it to an instantaneous (1 ms) flash of light [ 11 . Neither preexposure nor exposure at low temperature increases the efficiency of conventional direct autoradiography. We shall refer to the method described in this paper as indirect autoradiography. It is unsuitable for isotopes which emit lowenergy p particles such as 3H, i4C or 35S.