Autoradiography

Autoradiography of a Southern Blot

Autoradiography is a class of techniques in which the positions of radioactively-labelled biological material makes a "self-picture" by exposing X-ray film.

A Southern Blot filter is placed inside a light-proof casette box (left) and overlain with a sheet of X-ray film. The cassette is closed and left for several hours to several days. The radioactively-labelled DNA exposes the film, which when developed shows a pattern of black bands that indicate the positions of labelled DNA in the blot. Alignment marks in three of the four corners are made with special ink that also exposes the film. The blot can be aligned with the film by means of the three index marks (with thee marks, only one alignment is possible). In some experiments, the alignment can be used to locate a particular DNA band on the blot and cut it out, to recover the DNA for further experiments.