Use of secondary electron detectors for compositional studies on embedded biological material.

In a scanning electron microscope (SEM) the secondary electron (SE) detector collects SE from various sources (SE-I, SE-II, SE-III) as well as backscattered electrons (BSE). SE-II and SE-III are generated by BSE and therefore provide compositional data. In order to collect the compositional electrons in the SE and BSE signals, we employed specimens with little or no surface morphology. Thin and semithin sections of biological embedded material were utilized, conventionally stained and/or subjected to cytochemical or immunocytochemical procedures. The specimens were observed in a SEM equipped with SE detector (SED), BSE detector (BED) and transmission electron (TE) detector (TED). We drew the following conclusions: a) images by SED of thin sections give the same information as images by TED; b) images by SED of semithin sections provide complementary information with respect to those obtained in BSE and TE mode. Some parameters affecting the intensity and the quality of the signal collected were also considered. Finally we observed the same semithin sections in a transmission electron microscope (TEM) with a SE attachment. Images obtained by SED, BED and TED were fully diversified.