Progress towards an optimal specimen support for electron cryomicroscopy

The physical principles of electron-specimen interaction govern the design of specimen supports for electron cryomicroscopy (cryo-EM). Supports are constructed to suspend biological samples within the vacuum of the electron microscope in a way that maximises image contrast. Although the problem of specimen motion during imaging has been known since cryo-EM was first developed, the role of the support in this movement has only been recently identified. Here we review the key technological advances in specimen supports for cryo-EM. This includes the use of graphene as a surface for the adsorption of proteins and the design of an ultrastable, all-gold substrate that reduces the motion of molecules during electron irradiation. We discuss the implications of these and other recent improvements in specimen supports on resolution, and place them in the context of important developments in structure determination by cryo-EM.