Correlative Spectromicroscopy and Tomography
Figure 5: Comparison of TEM and STXM micrographs showing a correlation of Fe with Amyloid-like fibril morphology. (A–C) TEM images from an unstained cortical section of transgenic mouse tissue measured by STXM. The high-magnification TEM image shown in (B) was obtained from the dotted area shown in (A). (D) shows TEM images of unstained fibrillar structures located in a nearby area of the same section. (E) shows a STXM-derived Fe L2,3
map (OD710 –OD705 ) of the iron-containing
fragment shown in (D). The higher-magnification TEM image shown in (F) (from dashed rectangle in (D)) is typical of Aβ plaques. (Adapted from [11].) All data from TEM except (E) STXM.
beam has been shown to cause chemical changes such as reduc- tion of Fe(III) minerals [21]. Te stronger spectroscopic signal and less damaging beam of STXM XANES analysis, combined with its XMCD capability, allowed measurements of the Fe chemical and magnetic state in typical TEM thin specimens. Appropriate sample preparation is critical for these stud-
ies. It is oſten the case that a sample used for a lower-resolution method may need to be thinned to be suitable for a higher- resolution method. Still the correlative advantage is retained as long as the same sample region can be identified either from the intrinsic sample morphology or from fiducial markers such as letter grids. Of course the techniques used in the bone-implant study are not available to all researchers. Similarly the access to synchrotron STXM microscopes is limited. In both cases, advanced instrumentation is being acquired by many labs and more STXMs are being built (currently there are 20 operational with another 5 in development). Tus correlative approaches of the type exemplified in this article are likely to become more available in the near future. We note that this article summa- rizes the high points of references [3] and [11]. Te interested reader should consult these references for more detail.
Conclusion Correlative X-ray, electron, and ion microscopy approaches
allow greater coverage of spatial resolution and chemical sen- sitivities. Such correlative microscopy oſten provides insights
16
on materials structure, properties, and functions not attainable with any one technique alone. Tis article has highlighted two correlative studies involving STXM: an ET–APT–EELS-STXM study of a human bone-dental implant interface and a TEM– STXM study of Aβ plaques in the brain cortex of an APP/PS1 trans-genetic mouse. Together these results demonstrate the power of STXM and electron microscopy as complementary tools for correlative, multi-scale biomedical studies.
Acknowledgements Financial support was from the Natural Sciences and
Engineering Research Council of Canada (NSERC) Discovery Grant program. X.W. was supported by an Ontario Trillium Scholarship. Electron microscopy and atom probe tomography were performed at the Canadian Centre for Electron Micros- copy at McMaster University, a facility supported by NSERC and other governmental sources. Prof. Anders Palmquist and Dr. Furqan Ali Shah at the University of Gothenburg are grate- fully acknowledged for their significant role in the implant study cited in reference [3]. Scanning transmission X-ray microscopy data were acquired with the ambient STXM at the Canadian Light Source, which is supported by Canada Foun- dation for Innovation, NSERC, the University of Saskatchewan, the Government of Saskatchewan, Western Economic Diversi- fication Canada, the National Research Council Canada, and the Canadian Institutes of Health Research.
www.microscopy-today.com • 2019 March
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