Transmission electron microscopy (TEM) allows to directly visualize and characterize small biological particles, such as viruses, making it an indispensable tool for development of vaccines and pharmaceuticals. However, the manual TEM grid preparation protocol strongly depends on the skill of the operator and affects the preparation consistency. Here, we present a capillary-driven microfluidic device for negative stain TEM (nsTEM) grid preparation with minimal user interaction. The presented device could make TEM grid preparations more consistent and provide non-specialists access to biological TEM investigations.