Nano-Beam X-Ray Fluorescence Mapping (2D n-XRF)
Nano-Beam X-Ray Fluorescence Mapping (2D n-XRF) is an analytical technique designed for high-resolution elemental mapping on the nanometer scale. This method employs focused X-ray beams to precisely investigate the elemental composition and spatial distribution within a sample, making it an invaluable tool in nanotechnology, materials science, and geology. The exceptional sensitivity and resolution of 2D n-XRF allow researchers to visualize and quantify the distribution of elements, offering detailed insights into the chemical composition and heterogeneity of materials at the nanoscale. This capability is particularly significant in understanding the complexities of nanomaterials, catalysts, and biological specimens, contributing to advancements in fields ranging from semiconductor technology to environmental monitoring.
The versatility of 2D n-XRF extends its applicability to diverse scientific disciplines, enabling researchers to explore complex materials and nanostructures. This technique has proven instrumental in unraveling the elemental characteristics of semiconductor devices, guiding advancements in material design and quality control. Additionally, in environmental science and biological imaging, 2D n-XRF opens new avenues for studying elemental distributions at the nanoscale, fostering discoveries that have implications for technology and medicine. As researchers continue to harness the capabilities of 2D n-XRF, its role in advancing our understanding of nanomaterials and their applications in various domains becomes increasingly pivotal.
Environmental Materials
The K intensity maps in Fig. 1 illustrate the porous structure of biochar particles collected at different reaction times. The blue areas represent air above and within the particles, while other colors indicate the solid phase of the biochar. Chromium distribution was heterogeneous across particles, with increasing intensity over time. The LCF results from micro-XANES revealed a greater fraction of Cr(VI) on particle surfaces after 6 and 24 hours compared to 30 minutes. The micro-XANES spectra confirmed the presence of Cr(VI), which was not evident in the bulk sample, emphasizing the importance of complementary techniques. Despite the stability of biochar and Cr distribution within its structural material, the trapped Cr is expected to remain stable for an extended period due to decreased ion exchange effects and physical boundary protection. This stability hinders the desorption of contaminants deeper into the biochar particle.
Reference:
Peng Liu, Carol J. Ptacek, David W. Blowes, Y. Zou Finfrock, YingYing Liu. Characterization of chromium species and distribution during Cr(VI) removal by biochar using confocal micro-X-ray fluorescence redox mapping and X-ray absorption spectroscopy. Environment International 2020, 134, 105216.
https://doi.org/10.1016/j.envint.2019.105216.
Neurons Studies
The imaging of metal ions in primary neurons necessitates the use of a synchrotron-based XRF method, requiring a nano-focused high-energy beam. Nanoscopium offers high spatial resolution, enabling the detection of metal ion distribution at trace levels in the parts per million (ppm) concentration range. This technique has been successfully applied to visualize metal ions in various biological samples. Employing the Nanoscopium nanoprobe, they investigated the elemental distribution in intact neurons lacking amyloid precursor protein (APP-KO) and those treated with Aβ (Fig . 2a). Summative XRF spectra were normalized per image area (Fig. 2b), without normalization based on cell area or thickness. Analysis of the average size of iron (Fe) clusters, quantifying the average cluster area per cell, including soma and neurites, revealed a significant clustering of Fe in the treated neurons (p = 0.013) (Fig. 2c). This pronounced Fe clustering was not observed in untreated cells (Fig. 2d). Notably, there was no significant clustering of copper (Cu) ions, and Cu concentrations, as determined by inductively coupled plasma mass spectroscopy, did not show significant changes after treatment with Aβ(1–42) (data not shown).
Reference:
Gustavsson, N., Paulus, A., Martinsson, I. et al. Correlative optical photothermal infrared and X-ray fluorescence for chemical imaging of trace elements and relevant molecular structures directly in neurons. Light Sci Appl 10, 151 (2021).
https://doi.org/10.1038/s41377-021-00590-x
Battery Studies
Chemical characterization of carbon-coated lithium iron phosphate (LFP) using nano-XRF reveals two distinct chemical phases during cycling: (i) phase-separated Fe-phosphide nanoparticles alongside LFP (Fig. 3, A to E) and ( ii ) Fe -phosphide nanonetworks within the LFP particle (Fig. 3, F to M). The initial sample displays Fe-phosphide particles ranging from 100 to 1000 nm surrounding the LFP particle (Fig. 3C), consistent with prior electron microscopy findings. XANES spectra from Fe-phosphides align well with the Fe3P reference spectrum, showcasing a distinct pre-edge feature (Fig. 3E). Despite Fe(II) dominance in the absorption edge features, XANES spectra from mixed regions remain distinguishable due to the characteristic pre-edge feature. This underscores the superiority of highly sensitive nano-XANES through fluorescence over TXM-XANES, where pre-edge resolution is compromised. Approximately 5% of the field of view comprises the Fe-phosphide phase, determined from the fitted coefficients. Following partial (de)lithiation of the particles, phosphide nanophases (4%) form a network structure (Fig. 3, H and L) alongside Fe(II) and Fe(III) states. The varying concentration of phosphides between particles is evident, reaching about 18% in another partially (de)lithiated particle. This highlights significant concentration variations from one particle to another. The debated percolating phosphide nanonetworks may stem from the lack of chemically sensitive characterization tools with sufficient spatial resolution.
Reference:
A. Pattammattel et al. High-sensitivity nanoscale chemical imaging with hard X-ray nano-XANES. Sci. Adv. 6, eabb3615 (2020).
https://www.science.org/doi/full/10.1126/ sciadv.abb3615
Stroke Studies
In this study, the authors conducted a thorough investigation of elemental changes in the photothrombotic (PT) mouse model, a highly reproducible model simulating focal thromboembolic ischemic stroke in the cortex. Fig. 4 outlines the overall trends in the early post-stroke period for observable elements up to Zn, accompanied by H&E staining and a schematic reference. Within the stroke lesion, a reduction in P, S, K, Fe, Cu, and Zn is noted, while Cl and Ca exhibit a significant increase. Higher-resolution imaging (2 μm pixel size, Fig. 4d) provides limited structural details in the infarct core, except for Ca accumulations. Following tissue sectioning, air-drying precedes XFI imaging, leading to the formation of Ca-rich micro-crystals, resulting in the mottled appearance in the Ca map. The stroke lesion core, primarily consisting of necrotic tissue, undergoes spontaneous crystallization due to elevated Ca as the tissue dries. These micro-crystals, exhibiting autofluorescence, are artifacts resulting from sectioning and drying, lacking inherent morphological or structural information. While some regions in the infarct core show elevated Cl hotspots at higher resolution (right panel, Fig. 4c), the overall distribution of this element appears uniform at 30 μm pixel resolution, without enrichment in the micro-crystals. Importantly, in early post-stroke time points before maximal Ca concentration (ie, 30 μm elemental map in Fig. 4), elevated Ca is observed within the surrounding tissue of the infarct, not associated with concentrated microcrystals. Some of this difference in Ca distribution Loosely forms a halo, potentially indicating a boundary region between the stroke lesion core and cells undergoing recent excitotoxic changes.
Reference:
Pushie, MJ, Sylvain, NJ, Hou, H. et al. Tracking elemental changes in an ischemic stroke model with X-ray fluorescence imaging. Sci Rep 10, 17868 (2020).
https://doi.org/10.1038/s41598 -020-74698-2