Interdisciplinary Development of Eels Compositional Mapping

Abstract

Historically, electron energy-loss spectroscopy (EELS) in the electron microscope has evolved from work performed in biological as well as materials science and physics laboratories. The task of developing EELS compositional imaging for biological applications has been particularly challenging for two reasons. First, biological structures are radiation-sensitive and second, elements and compounds of interest are distributed sparsely in a multi-component matrix. For example, the physiologically important element, calcium, is typically present in cells at only 10-100 atomic parts per million.3,5 Even, when individual molecular components of a cell are isolated, elemental concentrations can still be low. Thus, double-stranded DNA contains only six phosphorus atoms per nanometer of its length; and protein molecules typically contain less than 0.5 per cent sulfur. This demand for high sensitivity in biological applications has provided an impetus to improve electron optics, to develop flexible image acquisition methods and to optimize spectral processing.