IMAGING THIN AND THICK SECTIONS OF BIOLOGICAL TISSUE WITH THE SECONDARY-ELECTRON DETECTOR IN A FIELD-EMISSION SCANNING ELECTRON-MICROSCOPE

A field-emission scanning electron microscope (FESEM) equipped with th e standard secondary electron (SE) detector was used to image thin (70 -90 nm) and thick (1-3 mu m) sections of biological materials that wer e chemically fixed, dehydrated, and embedded in resin. The preparation procedures, as well as subsequent staining of the sections, were iden tical to those commonly used to prepare thin sections of biological ma terial 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 s ections of tissues that were selectively stained using cytochemical an d immunocytochemical techniques. Furthermore, thick sections could als o be imaged in the SE mode. Stereo pairs of thick sections were easily recorded and provided images that approached those normally associate d with high-voltage TEM.