Measurement of water content in hydrated cryosections by EELS
Determination of cellular organelle water content is important in understanding cell volume regulation and also for converting x-ray microanalytical measurements of diffusible ions and elements from dry mass concentration to the biologically more relevant aqueous concentration. It has been proposed that electron energy loss spectroscopy (EELS) can be used to measure mass thickness in frozen hydrated and dehydrated cryosections at low electron dose, and that the method should thus provide a direct estimate of water content. Potentially the EELS inelastic scattering method has a number of advantages over alternative approaches. For example use of the x-ray continuum to measure mass requires much higher doses and cannot be applied at resolutions of 100nm to hydrated samples. Moreover, hydrated cryosections are often too thick to utilize dark field STEM imaging for mass measurement.