Electron spectroscopic imaging

Electron spectroscopic imaging (ESI) is a short term for electron energy loss spectroscopic imaging. ESI is to date the most sensitive electron microscopic analytical technique and has a spatial resolution of 0.5 nm and a mass resolution of less than 50 atoms. ESI takes advantage of filtered, inelastically scattered, transmitted electrons to form spectroscopic images. This analytical mode was developed by F. P. Ottensmeyer of the Ontario Cancer Institute in Toronto, Canada. Specimens to be analyzed by ESI should not exceed 30 nm in thickness so that multiple scattering of electrons is avoided. Isolated macromolecules constitute ideal specimens. For the analysis of diffusable elements, elaborate techniques involving quick-freezing, drying and embedded in plastic of the specimens have to be used. An example is given in which calcium was analyzed in the mitochondria of the convoluted proximal tubules in the rat kidney in normal and acute ischemic conditions. The example shows that calcium was not extracted during the preparation of the tissue. The high resolution of ESI allows the localization of calcium inside mitochondria. Experiments in progress using homogenous standards will soon render ESI entirely quantitative. It is concluded that ESI will become more and more important as a tool for the study of the pathogenesis of conditions in which modification of the distribution and concentration of elements are involved.