Cryo-EM Visualization of Nanobubbles in Aqueous Solutions

The detection of nanobubbles on surfaces is well established (e.g., AFM and optical microscopy methods), but currently no methods exist for the direct detection of bulk nanobubbles. Here, cryo-electron microscopy (cryo-EM) has been employed to observe bubbles in aqueous solutions for the first time. Nitrogen bubbles generated by a chemical reaction were observed in amorphous ice trapped between two carbon films. The cryo-EM images of bubbles showed the same features as predicted by theory. The fact that no bubbles were observed near an air–water interface suggests that bubbles may diffuse to the nearby air–water interface and escape. The estimate of the bubble diffusion coefficient is about 30–250 μm2/s.