Negative Stain in Transmission Electron Microscopy
Biological material is mainly composed of light atoms, and therefore has a low scattering power. In transmission electron microscopy, heavy metals can be used to increase the contrast of images of biological samples. The heavy atom salt will preferentially bind to the surface of the adsorbed particles, creating a "fingerprint" of the particles in the dye. A strong contrast is thus generated between the heavy metal-rich areas and the other regions (where the biological particles are located). The biological sample (mostly water) must also survive the high vacuum inside the microscope. In the case of negative staining, the fingerprint survives and its image is recorded.