Damage to biological samples caused by the electron beam during electron microscopy.

A new method has been developed which measures directly the beam damage suffered by biological specimens in the electron microscope. This method involves the use of radioautography to measure specific radioactivity of labeled specimens, either exposed or unexposed to the beam. Using this technique, it has been found that macromolecular samples such as ribosomes and R17 virions are severely damaged during standard electron microscopic operations: from 15 to 40% of the mass of the sample may be lost in a 30 sec exposure to the beam.