LIMITATIONS AND PROSPECTS OF BIOLOGICAL ELECTRON PROBE X-RAY MICROANALYSIS

Abstract

ABSTRACT Analytical electron microscopy is used to identify, localize and quantify chemical elements in biological samples with the aim to correlate the element distribution in cells and tissues with the particular functional state. Energy dispersive electron probe X-ray microanalysis of freeze-dried cryosections is considered to be the most efficient technique with respect to spatial analytical resolution and detection limit. The potentialities and limitations of this technique are illustrated by results from 3 current research projects: Element compartmentation in hepatocytes, cytotoxicity of an organotin compound, and calcium movements during osmoregulation of epithelia. At present, the absolute detection limit is 170 atoms in a minimum analytical volume of 30 × 30 × 100 nm3. X-ray microanalysis of cryosections from biological samples is limited by ice crystal growth during cryofixation and by the poor X-ray collection efficiency in most electron microscopes. Therefore, the construction of an analytical electron microscope dedicated to biological X-ray microanalysis is proposed. This microscope features considerably improved X-ray collection efficiency due to an annular X-ray detector. The absolute detection limit is estimated to be less than 10 atoms in a minimal analytical volume of 10 × 10 × 100 nm3 of a cryosection.