Vitrocam: A simple low cost Vitrobot camera for assessing grid quality

Abstract

The most widely used sample preparation method for single particle cryo-electron microscopy (cryo-EM) today involves the application of 3-4 l of sample onto a cryo-EM grid, removing most of the liquid by blotting with filter paper, then rapidly plunging into liquid ethane to vitrify the sample. To determine if the grid has appropriate ice thicknesses and sufficient area for cryo-EM imaging, the grid must be inserted into a transmission electron microscope (TEM) and screened. This process to evaluate grid quality is costly and time consuming. Here, we present our initial attempt to image the sample preparation process in one of the most commonly used plunge freezing devices, the Vitrobot. We do this by building the Vitrocam, a Raspberry Pi high-speed camera, that captures images of grids mid-plunge. Images from the Vitrocam can be correlated to TEM atlases and show promise for providing preliminary feedback on grid quality and ice thickness.