Synchrotron spectromicroscopy for the life sciences: General considerations and special procedures

The effort to apply synchrotron spectromicroscopy techA photon absorbed by a system can transfer its energy to one of niques to life science problems is definitely beyond the feasibility-test its electrons, enabling it to overcome the binding energy barrier stage. Furthermore, the commissioning of ultrabright, third-generation and to be ejected, becoming a ‘‘photoelectron.’’ soft–X-ray sources such as Elettra in Trieste or the advanced light The effect is extensively used as a fine and powerful chemical source in Berkeley has boosted this effort, most notably in the areas probe [7]. Consider, for example, the ejection of a ‘‘core’’ elecof scanning and electron-imaging photoelectron spectromicroscopy. tron which is strongly bound to one of the atoms of the system. Besides producing research results, the effort also develops new proThe ejected electron carries information on the atom: specifically, cedures and finds solutions for new conceptual problems. We first on the corresponding chemical elements and on its chemical stabriefly review the basic experimental techniques in this domain; then we discuss some specific experimental issues, such as the specimen tus, i.e., on its chemical bonds. Figure 1 provides a very simplified preparation problems caused by peculiar features of the techniques, picture of how this information can be extracted. This powerful e.g., their surface sensitivity. Third, we briefly present conceptual approach to chemical analysis has been extensively used for deconsiderations on the optimization of the data-taking procedures. cades [7] under the general name of ‘‘photoelectron spectrosFinally, we illustrate the applications in biology with a few specific copy’’ and more specific acronyms such as ESCA (electron specresearch examples, and analyze the probable future developments in troscopy for chemical analysis) . this area. q 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 188– Why, then, should one not combine photoelectron spectros203, 1997 copy with electron microscopy and perform the analysis on a microscopic scale? The answer, until quite recently, was that no photon source existed to obtain the required photon flux and