Biological Applications of X-Ray Contact Microscopy

Abstract

In their living state biological specimens are hydrated, composed of low atomic number molecules (predominately C, O, N, H) and exhibit some form of movement. All of these inherent characteristics make morphological examination of the tissue in it’s natural state difficult by conventional light and electron microscopy. To withstand the rigors of a light or electron beam (and vacuum) and provide adequate contrast for cellular or intracellular delineation, the biological sample must be chemically and/or physically treated. Chemical and cryofixation are commonly used to stabilize the cells and membranes of tissues so that the specimen may be carbon or metal coated, dehydrated and dried, or dehydrated and infiltrated with a supportive matrix such as plastic or wax to facilitate sectioning of the tissue prior to viewing. All of these procedures carry the risk of altering the elemental composition or ultrastructure of the tissue, and the question of whether data is real or artifactual must always be addressed. Each chemical treatment for tissue preparation risks the introduction of exogenous materials into the specimen, as well as the leaching and translocation of diffusible substances from specific cells.