Electron Diffraction, or MicroED, is another modern cryo-EM technique that delivers high-resolution data for a wide range of crystalline samples such as proteins, peptides, as well as organic molecules. Nano-crystals of the molecules of interest are required, which are deposited on an EM grid. The latter can also be blotted and flash frozen by plunging. Subsequently, the small 3D crystals are rotated continuously under the electron beam and at very low doses, while a high-speed detector records the diffraction data as a movie. The crystal structure can then be determined by using standard crystallographic software.
The Tecnai F20 200kV cryo-TEM is equipped with a cryo-tomography holder and an ASI hybrid detector (512 x 512), specifically designed for electron diffraction data. For larger crystals (1 µm or more), the Aquilos 2 can be used for milling thin lamellae (less than 300 nm), well suited for electron diffraction experiments.
General guidelines of sample requirements
Thin 3D crystals are required (of roughly ~200 nm thickness).