A technique to obtain quantitative water measurements from high-resolution STEM images of biological specimens

Abstract

Water content is an important parameter in many biological and medical investigations, such as volume regulation in cell biology, osmotic adaptation in physiology, and cell injury in pathology. Of existing methodologies for quantitative water measurements, analytical electron microscopy offers unique opportunities for absolute quantitation of water in subcellular volumes within any region of a tissue. Water quantitation by AEM analysis is typically done by measuring the x-ray continuum intensity in a freeze-dried specimen and comparing the continuum with that from a standard of known water content using the Hall or Rick approach. However, this AEM data is obtained at great cost in time, usually by stationary probe measurements. Often large numbers of analyses must be averaged to obtain meaningful results. Mass loss (etching) or mass gain (contamination) during analysis seriously complicates the water measurement. We have developed an alternative technique that eliminates or minimizes these problems. Our technique is similar to the Rick procedure, and similar assumptions apply.