Imaging Thin and Thick Sections of Biological Tissue with the Secondary Electron Detector in a Field-Emission Scanning Electron Microscope

Nematology Laboratory, *Soybean and Alfalfa Research Laboratory, †Horticultural Crops Quality Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, Maryland; ‡EM Facility, Unversity of Tennessee Knoxville, and Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA

Summary: A field-emission scanning electron microscope (FESEM) equipped with the standard secondary electron (SE) detector was used to image thin (70–90 nm) and thick (1–3 µm) sections of biological materials that were chemically fixed, dehydrated, and embedded in resin. The preparation procedures, as well as subsequent staining of the sections, were identical to those commonly used to prepare thin sections of biological material for observation with the transmission electron microscope (TEM). The results suggested that the heavy metals, namely, osmium, uranium, and lead, that were used for postfixation and staining of the tissue provided an adequate SE signal that enabled imaging of the cells and organelles present in the sections. The FESEM was also used to image sections of tissues that were selectively stained using cytochemical and immunocytochemical techniques. Furthermore, thick sections could also be imaged in the SE mode. Stereo pairs of thick sections were easily recorded and provided images that approached those normally associated with high-voltage TEM.