Date Published: October 01, 2017
Publisher: International Union of Crystallography
Author(s): Gergely Papp, Franck Felisaz, Clement Sorez, Marcos Lopez-Marrero, Robert Janocha, Babu Manjasetty, Alexandre Gobbo, Hassan Belrhali, Matthew W. Bowler, Florent Cipriani.
A sample changer based on a six-axis industrial robot and a new sample-storage dewar with an ice-cleaning feature have been developed to open automated X-ray crystallography beamlines to new sample-holder models, such as miniSPINE and NewPin, while remaining compatible with the widespread SPINE sample-holder standard.
Following the pioneering developments in automating sample transfer at macromolecular crystallography (MX) beamlines, and the standardization of sample holders used in cryocrystallography at the turn of the century (Cipriani et al., 2006 ▸; Cohen et al., 2002 ▸; Jacquamet et al., 2004 ▸, 2009 ▸; Ohana et al., 2004 ▸; Pohl et al., 2004 ▸), sample changers continue to develop to match the ever-increasing demand for storage capacity, transfer speed and fully automated data collection (Nurizzo et al., 2016 ▸; Russi et al., 2016 ▸; Ferrer et al., 2013 ▸). Currently, 15 distinct types of sample changer, six types of basket and six types of sample holder are deployed at the various MX beamlines around the world (http://smb.slac.stanford.edu/robosync/). Some of the existing sample changers are equipped with tool changers that are able to switch between standard data collection and in situ data collection (Jacquamet et al., 2004 ▸), but most are only compatible with a single sample holder and puck model currently used in cryocrystallography.
The most important aspect of a robotic sample changer is its ability to preserve the integrity of the crystals during transfer between the storage dewar and goniometer. The temperature at the position of the crystal should be maintained below 100 K and ice contamination avoided during transfer. These points are governed by the design of sample holders, the associated robot grippers and by the transfer speed. The temperature at the sample position in the grippers during the load and unload transfer processes was therefore measured, and the limits determined at which the diffraction quality starts to degrade against the transfer time and against repeated transfers of the same crystal. The repositioning precision of the different sample holders on the goniometer was also measured as it directly affects the time required to align crystals in the X-ray beam. All tests were carried out on the EMBL–ESRF–India BM14 beamline, with the ED8 filled with liquid nitrogen and the temperature of the cryo-jet set to 100 K. The tip of the cryo-jet head was adjusted to a distance of 5 mm from the nominal position of the crystals and a 3 mm retraction was systematically applied during the gripper approach to avoid collision, although this is only necessary when transferring SPINE/SPINEplus sample holders.
A fast, flexible and reliable sample-changer family based on an industrial six-axis robot has been developed. The FlexED8 model described in this article allows a single beamline to accept both the popular SPINE sample holder and the newly developed high-density miniSPINE as well as NewPin sample holders. A sample-storage capacity of 252 samples is achieved with seven pucks stored in an open, 40 cm diameter, self-cleaning dewar (EdgeDewar ED8). Overall, the FlexED8 offers a compact, easily accessible, ice-free, high-capacity cryogenic sample-storage system. The nominal sample-exchange time of 40 s is reduced to less than 5 s for SPINE sample holders when a double gripper is used (Supplementary Fig. S2), and the development of a double gripper for the NewPin and miniSPINE sample holders is ongoing. The FlexED8 sample changer has been successfully tested on the EMBL–ESRF–India beamline BM14. Crystals were reliably transferred from the EdgeDewar to the goniometer without ice contamination and maintained at a temperature below 100 K throughout the loading and unloading procedures with a comfortable safety margin. The repositioning precision of ±3.5 µm obtained with the NewPin sample holders through successive loading and unloading cycles should decrease the duration of crystal alignment at beamlines and make it potentially unnecessary for crystals harvested by automated systems that provide the coordinates of the crystals (Svensson et al., 2015 ▸; Zander et al., 2016 ▸). The Flex sample-changer family is equipped with a tool-changer system that allows an expansion of the handling capabilities. An example is a gripper for SBS crystallization plates (Supplementary Fig. S6) currently under development that will be used in two different environments. Firstly, on ESRF beamline ID30B it will be deployed to automatically mount SBS crystallization plates stored in a hotel onto the plate holder of the MD2S goniometer for in situ data collection (Supplementary Fig. S7; FlexHCD). Secondly, it will be used at the crystal-harvesting station of the high-throughput crystallization laboratory of the EMBL Grenoble Outstation to transfer crystallization plates from the imaging systems (Formulatrix Rock Imager 1000) to the CrystalDirect harvester (Supplementary Fig. S7; FlexED3).