Elemental mapping of frozen-hydrated cells with cryo-scanning X-ray fluorescence microscopy

Visualizing the elemental distributions of cells and tissues is of growing importance in biology and medical science because such data deepen our understanding of the behavior of metal-binding proteins and ions. Elemental mapping by X-ray fluorescence analysis with a hard X-ray nanobeam is very well suited for this purpose owing to its high sensitivity and high resolution. Using this technique, samples must be prepared without artifacts that are caused by treatments such as chemical fixation and staining procedures. In many studies of elemental mapping, sample preparation is not explicitly considered. To overcome this deficiency, we developed a cryo-scanning X-ray fluorescence microscope and installed it in the second experimental hutch of BL29XUL of SPring-8. We used it to observe frozen-hydrated cells that had been fixed by a quick-freezing technique to preserve elemental data of the living state at an X-ray energy of 11.5 keV. The distributions of K, Ca, Fe, Cu and Zn were successfully visualized. The distributions of these elements (especially those of K, Ca and Fe) differed from those in cells fixed with paraformaldehyde. Copyright (C) 2010 John Wiley & Sons, Ltd.