Valence Electron Energy Loss Spectroscopy of Lipids

Abstract

We have recently demonstrated that chemical mapping by valence electron energy loss spectroscopy (EELS) can provide water distributions in frozen hydrated biological specimens. That investigate also considered the EELS spectra from proteins, nucleic acids and lipids. Next to proteins, lipids the second most abundant component of eukaryotic cells in terms of their mass fraction, but since lipids usually contain a high fraction of saturated carbon bonds they are particularly sensitive to radiation damage in the electron microscope. Here we characterize in further detail the valence EELS spectra of various lipids (arachidic acid, carotene, cholesterol and phosphatidylethanolamine) to determine what information is available about the ratio of saturated and unsaturated bonds and how the EELS fine structure changes as a function of dose.