W0133

Fully Automated Cryogenic Crystal Screening System. J. Kaercher, F. Jin, R. Lancaster, S. Leo, B. Michell, V. Sedov, B. He, M. Ruf, R. Durst, Bruker Advanced X-ray Solutions, Madison, WI, U.S.A.

Sample changing of single crystals, manual until very recently, has been automated by the BruNo robotics system that takes the cryo-cooled sample from a liquid-nitrogen storage dewar and mounts it on the goniometer, then after the screening, retrieves and stores it for future experiments. For this procedure, proprietary Kryo-Vials™ are used to transport the crystals to and from the storage dewar at liquid-nitrogen temperatures, yet do away with the liquid itself, assuring a straightforward and much safer sample handling.

An automated goniometer head centers the crystal in the X-ray beam. The software uses a least-squares based algorithm to determine the crystal position in three-dimensional space, first by finding the loop position from a series of images taken by a high resolution digital zoom microscope, then by using X-ray diffraction.

The screening process takes two short series of X-ray diffraction images, from which the general quality of the crystal is judged by the resolution limit, the mosaicity, the ability to find the unit cell, and the presence of ice rings. User input limits for the unit cell volume help to distinguish between the actual sample and unwanted crystals, such as from buffers or salts co-crystallized with a protein.

Compared to the laborious and time-consuming manual sample mounting and screening, the Bruker Nonius robotics system and software will speed up preparation by an order of magnitude.