Autoradiography Protocol

Scientists routinely label molecules with radioisotopes to track them experimentally. Autoradiography is a method that uses X-ray film, which is sensitive to beta particles and gamma rays, to visualize the position of those radioactive molecules in an experiment.

Example

Molecular biologists use radioisotopes to find particular sequences of DNA. Fragments of DNA can be separated by size in gels with an electrical field, and similarly transferred to a thin membrane. A radio-labeled DNA fragment of known sequence, or a probe, binds to identical sequences on the membrane. Exposing the membrane to X-ray film pinpoints the location of those radioactive sequences on the membrane.

Autoradiography

In a darkroom, the film is placed on top of the membrane and sealed in a cassette, a metal container to prevent exposure to light, for storage. The exposure time depends on the intensity of the probe. After exposure, the film is removed from the cassette in the darkroom and placed in an automatic film developer.

Intensification

Intensifying screens, which release photons when hit by particles, can be used with higher energy isotopes to boost the signal on the film. The film is sandwiched between the membrane and screen, placed in a cassette and stored at -112 degrees Fahrenheit until it is developed.

References

• Bart's Cookbook: Exposing Gels and Plates Containing Radioactive Samples to X-Ray Film
• Molecular Station: Autoradiography and Intensifying Screens