Prescott's Microbiology 8th Edition by Joanne Willey, Linda Sherwood, Christopher J. Woolverton, Lansing Prescott, John Harley, Donald Klein

Exercise 4

Under what circumstances would it be desirable to prepare specimens for the TEM by use of negative staining? Shadowing? Freeze-etching?

Step 1 of 3

Negative staining is typically carried out for imaging virus particles and studying organelles of differing densities compared to the cytoplasm (e.g. gas vacuoles).

The specimen is coated with a stain such as phosphotungstic acid. The stain does not enter the sample. As the electron beam passes through the sample, the stain and the sample deflect it. Deflection is less where the sample excludes the stain.

Thus, the background of the image will be dark and the specimen will be lighter. Objects within the cell that are of different densities deflect the electron beam differently and can be differentiated from the surrounding area.