The X-MaxN series of large-area SDD detectors from Oxford Instruments are advancing the EDS analysis of biological samples. They have a sensor active area of up to 150mm2 and allow the integration of multiple detectors to achieve an effective area of up to 600mm2, thereby optimizing the counts from samples even at low kV and small spot sizes.
The advent of these large area SDD detectors not only makes ultra-fast analysis and nano-scale accurate mapping on biological materials possible, but practical too.
Fast Mapping with Multiple Detectors
The potential of EDS analysis for beam sensitive and cryogenically frozen samples has been greatly improved by the launch of large area SDD detectors with unprecedented light element performance.
The capabilities of these highly sensitive spectrometers can be further expanded by mounting multiple detectors on the same microscope (Figure 1).
Figure 1. Fast Mapping with Multiple Detectors
EDS Mapping of Wheat
Figure 2 illustrates the results of a biological sample analysis on a Tescan MIRA fitted with three X-MaxN 150 detectors. After embedding the wheat sample into a Spurr type resin, it was stained with Osmium to show up the fatty acids in the sample.
Then EDS analysis of the aleurone cell microstructure was performed to see the possibility of differentiating the phosphorus-rich protein granules (depicted in black in Figure 2b) and the oil bodies surrounding them (must appear rich in Os).
Figure 2. Electron micrographs showing the microstructure of a wheat aleurone cell (Image and samples provided courtesy of Jean Devonshire, Rothamsted Institute).
EDS maps were acquired at a low accelerating voltage (4kV) to make comparison of the results observed on a conventional EDS system with those now achievable using the new large area SDD detectors (Figure 3).
The results are outstanding. Figure 3a depicts the maps collected using a conventional 10mm2 SDD detector in just one frame, showing only very few counts, which are inadequate to make out any statistically significant structures.
Figure 3. EDS maps of wheat aleurone cell microstructure comparing different analysis systems
The same data when collected on the multiple detector system clearly shows the P-rich protein bodies as is the structure of the Os stained oily bodies (Figure 3b). The data also shows nanostructures with one identified protein body measuring 300nm wide.
All of this data was obtained in one frame and the acquisition time was just 3 minutes. Even counting for much longer (Figure 3c) does not provide additional details beyond what is already obtained in just one frame.
The high sensitivity and very large active area provided by multiple detector systems is useful to analysts interested in the analysis of highly beam sensitive materials or biological matter. The high collection efficiency enables users to perform cryogenic sample analysis rapidly and accurately, optimizing count rates at low kV and small spot sizes and with reduced beam damage.
This information has been sourced, reviewed and adapted from materials provided by Oxford Instruments Nanoanalysis.
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