'A spectroscopic picture paints 1000 words' mapping iron speciation in brain tissue with 'full spectrum per pixel' X-ray absorption near-edge structure spectroscopy

Coordination chemistry enables a variety of vital functions in biological systems; however, characterising the chemical form of metal ions in cells and tissue is notoriously difficult. One technique that is gaining substantial momentum in this research area is X-ray absorption near-edge structure (XANES) spectroscopy. The XANES spectrum can be a rich source of information with respect to the coordination environment of metal ions. Further, XANES spectroscopy is compatible with microscopy mapping protocols as the spectra are recorded across a relatively narrow range of data points (typically 50–100). Although the potential of XANES spectroscopy to study metal ion coordination chemistry has long been known, data collection speed has only relatively recently reached the state in which maps can be collected with a full spectrum per pixel. The realisation of this capability now places XANES spectroscopic mapping among a suite of other spectroscopic imaging techniques, such as Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy, which are available to characterise biochemical composition, in situ within cells and tissue. Herein, we report a proof-of-concept application of XANES spectroscopic mapping to begin exploration of Fe speciation in brain tissue, which demonstrates the potential of this method for the biomedical sciences, and identifies important areas for consideration with respect to future protocol developments.