Fig. 4: (Cryo)-TEM micrographs and fluorescence microscopy.

a Negative stain using uranyl acetate of a reaction starting with 0.2 m acetaldehyde and 5 mol% catalyst loading after 6 h. Scale bar: 1 μm. The uniform partial circle is a hole in the holey carbon-supported grid. b, c Cryo-TEM image of a reaction using 0.5 m acetaldehyde with 5 mol% catalyst loading after 1 h. Scale bar: 100 nm. A water enriched oil droplet b and significantly smaller structures c are visible. d, e, and f Fluorescence microscopy of a reaction using 0.5 m acetaldehyde with 5 mol% catalyst loading developing over time. Orange: nonpolar probe rhodamine B. Scale bar: 5 μm. d Initial oil droplet formation. e droplet with water accumulation. f Protocell structure. g Proposed model for protocell formation.