Microchemical Element Imaging of Yeast and Human Cells Using Synchrotron X-ray Microprobe with Kirkpatrick−Baez Optics

Abstract

Trace element imaging and speciation analysis in cells and subcellular compartments is a challenging and important objective for modern analytical chemistry in order to better understand the biological chemistry of essential and toxic elements. A focusing system based on Kirkpatrick−Baez design optics mounted on a synchrotron radiation scanning X-ray microscope has been developed at the ESRF and was used for trace element quantitative imaging in single cells. The focused microbeam (1.3 × 3.2 μm²) obtained in that way led to a photon flux as bright as 1.5 × 10¹¹ photons/s at 14 keV. The absolute detection limit of this analytical probe, as measured on standard reference materials, was shown to be 2 × 10^-17 g for most elements. Chemical maps of human carcinoma and of Saccharomyces cerevisiae cells were obtained for minor (P, S, Cl, K) and trace elements (Fe, Zn). Within human cancer cells, chemical elements are homogeneously distributed at the current spatial resolution and correlated with the sample's mass, except Fe, which shows micrometer-sized structures around the cell nucleus, and Zn, which slightly concentrates in the nucleus, while chemical maps of S. cerevisiae show homogeneous pattern distribution at the cellular level.