Development of a non-destructive micro-analytical method for stable carbon isotope analysis of transmission electron microscope (TEM) samples

The biogenicity of ancient morphological microfossil-like objects can be established by linking morphological (e.g. cell remnants and extracellular polymeric matrix) and chemical (e.g. isotopes, biomarkers and biominerals) evidence indicative of microorganisms or microbial activity. We have developed a non-destructive micro-analytical ion beam system capable of measuring with high spatial resolution the stable carbon isotope ratios of thin samples used for transmission electron microscopy. The technique is based on elastic scattering of alpha particles with an energy of 2.751 MeV. At this energy the ¹³C cross section is enhanced relative to the pure Rutherford cross section for ¹³C, whereas the ¹²C cross section is reduced relative to its pure Rutherford cross section. Here we report the initial results of this experimental approach used to characterize ultramicrotomed sections of sulfur-embedded graphite and microbial cells.