MicroED

Microcrystal electron diffraction (MicroED or 3DED) is an electron microscopy technique that utilises electrons rather than X-rays to study crystal structures. Electrons, due to their charge, have a stronger interaction with matter and this allows diffraction data to be collected from crystals 10s to 100s of nm in size, almost a billion times smaller than those typically used in X-ray diffraction experiments. This brings samples that had previously proven impossible to study within reach of structural biology/ chemistry.

At its core, microED utilises a transmission electron microscope (TEM) operating in diffraction mode. As such, it has benefitted from much of the software and hardware developments in TEM over the past decade, particularly those used in cryoEM. MicroED requires a sample to be continuously rotated under a parallel electron beam whilst a high-speed camera continually captures diffraction data. This data can then be analysed using conventional crystallographic software developed for X-ray diffraction with some minor modifications. Typically, multiple crystals will be analysed in this way to obtain a structure.

MicroED has seen rapid adoption in the past few years, especially as applied to organic and synthetic chemistry. ED’s ability to bypass the need for time consuming recrystallisation experiments has increased both the number of chemical structures that can be solved as well as decreasing the time between synthesis and structure. For structural biology, microED has seen interesting applications in the fields of membrane biology, amyloidosis and “in cellulo” crystallisation.

At the Franklin, we are seeking to push the boundaries of microED capabilities in terms of complexity of sample and throughput of results. We are exploring how new hardware, such as electron counting and event-based detectors, which will improve the quality of recorded diffraction data and reduce the time needed to record individual rotation datasets. We are also exploring new sample preparation methodologies that will allow samples of high complexity, whether due to composition or formation, to be studied by ED. Alongside method development, we are applying microED to questions in high-throughput and novel chemistries, radiation damage, charge transfer and catalysis, and sub-cellular organisation.