Rubinstein, J. L.; Guo, H.; Ripstein, Z. A.; Haydaroglu, A.; Au, A.; Yip, C. M.; Di Trani, J. M.; Benlekbir, S.; Kwok, T. Shake-it-off: a simple ultrasonic cryo-EM specimen-preparation device. Acta crystallographica. Section D, Structural biology, 2019, 75, 1063-1070
Although microscopes and image-analysis software for electron cryomicroscopy (cryo-EM) have improved dramatically in recent years, specimen-preparation methods have lagged behind. Most strategies still rely on blotting microscope grids with paper to produce a thin film of solution suitable for vitrification. This approach loses more than 99.9% of the applied sample and requires several seconds, leading to problematic air-water interface interactions for macromolecules in the resulting thin film of solution and complicating time-resolved studies. Recently developed self-wicking EM grids allow the use of small volumes of sample, with nanowires on the grid bars removing excess solution to produce a thin film within tens of milliseconds from sample application to freezing. Here, a simple cryo-EM specimen-preparation device that uses components from an ultrasonic humidifier to transfer protein solution onto a self-wicking EM grid is presented. The device is controlled by a Raspberry Pi single-board computer and all components are either widely available or can be manufactured by online services, allowing the device to be constructed in laboratories that specialize in cryo-EM rather than instrument design. The simple open-source design permits the straightforward customization of the instrument for specialized experiments.