Thickness measurements of wet protein crystals in the electron microscope

With the stable environment afforded by a dynamically pumped wet specimen chamber, the thickness of a fully hydrated protein microcrystal may be obtained in an electron microscope from an incident-beam attenuation measurement after disappearance of the diffraction pattern. Such measurements on orthorhombic catalase crystals have been successfully cross-correlated with thickness measurements on the same crystals made with an interference light microscope over a range from a few hundred to a few thousand Ångströms.