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Sometimes less is more: microfluidics extends the capabilities of SAXS
Katrine Toft
A high-resolution image of a person have not been fully automated. Further- experimental conditions are optimized, can provide a lot of information about more, experimental conditions have not the low-resolution shape reconstruction the person at one particular moment, been easy to change, because the sample can be obtained from an indirect FT of but it doesn’t necessarily give you an cell is placed in a vacuum chamber. the data followed by ab initio modeling. idea of what the person was First, to demonstrate the doing before the image was reproducibility of the automade or what the person will mated mixing and the quality do next. On the other hand, a of the data when such a small series of low-resolution images sample volume is used, the taken over a period of time authors performed a dilucan provide more information tion series with BSA. One about what the person was experimental cycle (including doing and will do, although mixing and washing) was peryou cannot see the person formed in 28 minutes (min). as clearly. Jörg Kutter uses a When using the device for similar analogy to describe the 24 hours continuously, the complementary nature of the team members didn’t see any protein-imaging system that evidence of leaking, clogging, he, Katrine Toft, and their Schematic of the BioXTAS high-throughput system for SAXS. X-ray-induced damage, or colleagues at the Technical contamination. Then, they University of Denmark, the University Toft says that the new, automated sys- added increasing amounts of SDS to the of Copenhagen, and Novo Nordisk A/S tem, called bioXTAS, allows researchers BSA solution to show that they could (Denmark) have developed. As reported to adjust buffers “on the fly.” It comdetect the gradual unfolding of the proin their recent AC article (2008, 80, bines a microfluidic mixer and a mintein. The researchers tried with limited 3648–3654), the group has combined a iature SAXS cell on a single chip; this success to make BSA refold by adding microfluidic front end with small-angle minimizes the dead volume of the samα-cyclodextrin to compete with BSA for X-ray scattering (SAXS) to yield a sysple and facilitates sample transfer. The binding to the SDS. tem that can determine low-resolution disposable bioXTAS polystyrene chips Acquisition times and detection limprotein structures on very small volhave sample chamber volumes of either its for SAXS experiments are dictated umes in an automated fashion. 200 or 500 nL and an X-ray path length by the X-ray source; with bioXTAS, the Popular high-resolution techniques of 1 mm. An aluminum chip holder with use of more powerful sources can reto determine the structure of proteins O-rings seals the connections to the chip duce the exposure times from 5 min to include electron microscopy and X-ray and external devices. “Interconnections
