X-ray centering depends on reproducible sample positioning and a fast detector. MASSIF-1 uses a PILATUS3 X 2M that can acquire up to 250 images per second. "Half of the six minutes it takes to measure the average sample is spent centering the crystal," explains Matthew Bowler, Beamline Scientist at MASSIF-1. "Full automation just wouldn't be feasible with a slower detector." Centering by diffraction depends on the scoring of images based on radial intensity above background, impossible on anything but a noise-free detector like PILATUS3.
How do crystallographers react to their precious samples being taken from them and exposed to X-rays without their oversight? "The service has now been running for 3 years and is proving very popular," says Bowler. "We have now processed over 35,000 crystals, and many structures have been solved de novo by SAD." The quality of automatically collected data is often better than that of data collected by human experts and untainted by sleep deprivation and bungled circadian clocks.
While MASSIF-1 accepts all kinds of samples, it really shines when repetition is highest. It will tirelessly screen hundreds of poor crystals to identify the few that diffract to high resolution. It will then, without breaking for lunch, collect hundreds of datasets of crystals soaked with a large library of compounds or fragments to help the user identify ligands. "It is such a waste to stay up for 24 hours to collect data," says Bowler. "This time can be used much better to find answers to the underlying biological questions."