MicroED with the Falcon III direct electron detector

Microcrystal electron diffraction (MicroED) combines crystallography and electron cryomicroscopy (cryo-EM) into a method that can be used for high-resolution structure determination. In MicroED nanosized crystals, often intractable by other techniques, are probed by high-energy electrons in a transmission electron microscope and the diffracted signal is recorded on an electron detector. Since only a small number of different detectors have been used for MicroED measurements in the past, their impact on data quality has not been investigated. Here we evaluate two different cameras using crystals of the well-characterized serine protease proteinase K. Compared to previously used equipment, the Falcon III direct electron detector and the CMOS-based CetaD camera can collect complete datasets both faster and using lower total exposure. As an effect of the lower dose, radiation damage is reduced, which is confirmed in both real and reciprocal space. The increased speed and lower exposure requirements have implications on model quality and the prospects for further automation of MicroED.