Small Angle X-ray Scattering (SAXS) is used to study the structure of materials in the 1 nm to ~200 nm range, and sometimes even larger. The materials typically studied include polymers, metals, colloids, liquid crystals and biological samples e.g. proteins (also referred to as Bio-SAXS). Bio-SAXS is a very useful technique as a complement to Protein Crystallography.
The information determined relates to the particle size, shape, distribution and orientation, porosity, surface features and internal structure.
A SAXS sample requires very little preparation and results are representative of the bulk material. The scattered signal is typically recorded at diffraction angles of <6° and the sample is positioned at a long distance from the detector. The measured scattered signals are accordingly extremely weak. For this reason, SAXS measurements benefit from the use of a high brilliance X-ray source such as the MetalJet, which makes weak scattering effects, stronger, more visible and more readily studied.
In-lab SEC-SAXS for structual investigation of protein samples
SAXS can be used to investigate biological macromolecules especially in monodisperse solutions.
However liquid bio-solutions involve structurally different molecules and complexes in dynamic equilibria.
SEC – Size Exclusion Chromatography has evolved as a technique to mitigate this by separating the molecules in time.
However this limits the measurements time window which put huge
requirements on the X-ray source.
With MetalJet source in the Xenocs BioXolver system it is possible to
perform protein in-lab SEC-SAXS even for very diluted solutions containing
less than 1 mg of sample.
Application note kindly provided by Application Scientist at Xenocs SAS using a BioXolver equipped with Metaljet X-ray source.
Bucciarelli, S. et al. Size-exclusion chromatography small-angle X-ray scattering (SEC-SAXS) of water soluble proteins on a laboratory instrument, J. Appl. Crystallogr. 2018
Application scientists at Bruker AXS have used a NANOSTAR instrument equipped with an Excillum MetalJet (200W at 70kV) to record a series of SAXS scattering plots of a very thin fibre from a rat tail tendon. Providing intensity gains of more than 50x compared to state-of-the-art sealed microfocus tubes.
Researchers at Nanyang Technical University, A*STAR, University of Louisville, Rosalind Franklin University of Medicine and Science and Kyung Hee University have used a MetalJet equipped SAXS instrument to study the BclxL protein, a key regulator in mitochondrial calcium ion transport. The protein was treated with a mild detergent and studied during the formation of a dimer resulting from three-dimensional domain swapping (3DDS) of helices α6-α8 between two monomers.
Researchers at the Slovak Academy of Science and STU Centre for Nano-diagnostics performed in-situ tests on a strain gauge, based on a monolayer of colloidal gold nanoparticles deposited on a flexible Mylar foil. The tests were monitored by SAXS where the high brightness of the Excillum MetalJet allowed a very fast data collection, with 10 seconds temporal resolution.
The investigation of polymers is one of the main areas of focus of the Soft Matter Analytical Laboratory (SMALL) at the University of Sheffield. Following a £2 million infrastructure investment in 2016 and the purchase of a new SAXS system with a gallium MetalJet X-ray source, their first new resulting publication was a co-polymerisation study of Styrene with N-Phenylmaleimide.
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