Small Angle X-Ray Scattering (SAXS)

In standard X-ray diffraction (XRD), an X-ray source illuminates the sample and characteristic diffraction patterns are formed due to the constructive interference of X-rays diffracting from the sample’s atoms. In particular, crystalline samples create sharp diffraction patterns due to the crystal lattice’s regular spacing of atoms. The mathematical relation that governs this process, Bragg’s Law, relates the diffraction angle to the X-ray wavelength and the lattice spacing in the sample. A consequence of Bragg’s Law is that small scattering angles are associated with spacings that are longer than typical interatomic spacings. Thus, small-angle X-ray scattering (SAXS) probes larger scale structures, such as those that occur in macromolecules like synthetic polymers or biomolecules. This analysis can be used for the testing and development of advanced materials and coatings, as well as for basic research into biomolecular structures. SAXS is nondestructive and typically requires little sample preparation, compared to conventional single-crystal XRD. Although most XRD systems could conceivably be used to carry out SAXS, there are difficulties with the technique, which makes dedicated systems valuable. The small scattering angles used in the technique result in the faint scattered beam being relatively close to the powerful main beam. Resolving the signal requires longer path-lengths and highly collimated beams. As with many X-ray techniques, higher beam powers are desirable. For this reason, SAXS has commonly been performed using custom instruments at beamlines in synchrotron facilities around the world. Since time at a beamline is both costly and limited, this has fostered the development of commercial SAXS instruments using laboratory X-ray generators. Polymer analysis is one of the major applications of SAXS, and high-powered systems can even provide time-resolved measurements of polymer crystallization. Other nanoscale materials and structures can also be studied with SAXS. With biological samples like proteins and DNA, the relatively simple sample preparation means that SAXS can provide important structural information about these molecules in a more natural environment. Also, time-resolved studies can shed light on interactions between biomolecules. Prices for SAXS systems vary a great deal depending on the X-ray source, X-ray optics and detector used in a system. The major X-ray instrumentation suppliers all compete in this market with dedicated SAXS systems. Bruker and Rigaku offer their own systems, while PANalytical markets the SAXSess system manufactured by Anton Paar. In addition, there are a few smaller players that have a greater emphasis on SAXS in their product offerings. Among these are inel, Hecus and Forvis. Mainly due to its application in protein analysis, SAXS is a rapidly growing technique, with 2007 sales of about $13 million for dedicated laboratory systems. SAXS at a Glance: Leading Suppliers • Bruker • Rigaku • Anton Paar Largest Markets • Polymers • Coatings • Biotechnology Instrument Cost • $175,000 and up

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