X‐ray fluorescence microprobe imaging in biology and medicine

Abstract

Characteristic X-ray fluorescence is a technique that can be used to establish elemental concentrations for a large number of different chemical elements simultaneously in different locations in cell and tissue samples. Exposing the samples to an X-ray beam is the basis of X-ray fluorescence microscopy (XFM). This technique provides the excellent trace element sensitivity; and, due to the large penetration depth of hard X-rays, an opportunity to image whole cells and quantify elements on a per cell basis. Moreover, because specimens prepared for XFM do not require sectioning, they can be investigated close to their natural, hydrated state with cryogenic approaches. Until several years ago, XFM was not widely available to bio-medical communities, and rarely offered resolution better then several microns. This has changed drastically with the development of third-generation synchrotrons. Recent examples of elemental imaging of cells and tissues show the maturation of XFM imaging technique into an elegant and informative way to gain insight into cellular processes. Future developments of XFM-building of new XFM facilities with higher resolution, higher sensitivity or higher throughput will further advance studies of native elemental makeup of cells and provide the biological community including the budding area of bionanotechnology with a tool perfectly suited to monitor the distribution of metals including nanovectors and measure the results of interactions between the nanovectors and living cells and tissues. Key words: X-ray fluorescence microscopy; elemental maps; metalome; bionanotechnology The biology of the past decade has significantly changed scope, and large compendia of data have been accumulated to enable scientists to study biological ''meta units'' such as the genome, proteome, and transcriptome. At this time, the term ''metalome'' is still used only rarely, and the majority of scientists interested in establishing metalome databases undertook the daunting task of developing and using different dyes for different elements and their ions in order to determine elemental locations and concentrations in cells and tissues. The presence of metals and trace elements is essential for the existence of life as we know it. In any organism, there are very few intracellular processes that are not dependent on the presence of metals or other trace elements. In fact, it is estimated that one-third of all known proteins contain metal cofactors and the majority of these function as essential metalloenzymes. With current developments in genomics and proteomics, our knowledge of the enormous number of pathways in which metals and trace elements are necessary for life is ever increasing. This knowledge, however, is largely ''static'' as we still do not have appropriate sensitive approaches to follow fluctuations in normal metal homeostasis that accompany processes of development, differentiation, senescence, stress responses, etc. Likewise, our knowledge about the redistribution of metals and trace elements accom...

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