Hard X-ray fluorescence tomography - an emerging tool for structural visualization

Hard X-ray fluorescence microscopy is well-suited to in-situ investigations of trace metal distributions within whole, unstained, biological tissue, with sub-parts-per-million detection achievable in whole cells The high penetration of X-rays indicates the use of X-ray fluorescence tomography for structural visualization and recent measurements have realised sub-500-nm tomography on a 10-mu m cell Limitations of present approaches impact the duration of an experiment and imaging fidelity Developments in X-ray resolution, detector speed cryogenic environments and the incorporation of auxiliary signals are being pursued within the synchrotron community Several complementary approaches to X-ray fluorescence tomography will be routinely available to the biologist in the near future We discuss these approaches and review applications of biological relevance