Room-temperature macromolecular crystallography using a micro-patterned silicon chip with minimal background scattering

Recent success at X-ray Free Electron Lasers have led to serial crystallography experiments staging a comeback also at synchrotron sources. With crystal lifetimes typically in the millisecond range and latest generation detector technologies with high framing rates up to 1 kHz, fast sample exchange has become a bottleneck for such experiments. We have developed a micro-patterned chip from single crystalline silicon which acts as a sample holder for up to thousands of microcrystals at a very low background level. The crystals can be easily loaded on the chip and excess mother liquor can be efficiently removed. Dehydration of the crystals is prevented by keeping them in a stream of humidified air during data collection. Further sealing of the sample holder, e.g. with Kapton, is not required. Room-temperature data collection from insulin crystals loaded onto the chip proves the applicability of the chip for macromolecular crystallography. Subsequent structure refinements reveal no radiation damage induced structural changes for insulin crystals up to a dose of 565.6 kGy, even though the total diffraction power of the crystals has on average decreased to 19.1 % of its initial value for the same dose. A decay of the diffracting power by half is observed for a dose of D1/2 = 147.5 ± 19.1 kGy, which is about 1/300 of the dose before crystals show a similar decay at cryogenic temperatures.