A Guide to Fixation and Staining of Biological Samples for Electron Microscopy

Abstract Proper fixation and staining of biological samples for electron microscopy (EM) is critical for preserving ultrastructure and providing sufficient contrast for imaging. Depending on experimental goals, different fixation and post-fixation staining methods can be chosen to elucidate the details needed to answer scientific questions. In this guide, we discuss the importance of primary fixation of biological samples and then focus on two major post-fixation staining schemes: the “TOU” and the “OTO” methods, with and without modifications, for highlighting specific structures within the tissue being examined. While both methods can be used for transmission (TEM) and scanning electron microscopy (SEM), we discuss which imaging technique is best suited for each method.