Figure 2. Verification of folding.

a) Cubes are folded in 1:1 stoichiometry and with 40 mM MgCl₂ (magnesium screening in Supporting Figure S3). Successful folding of cube structures is proven by means of gel electrophoresis, resulting in a clear band separated from unfolded or excess strands. b) TEM images of folded and gel purified cube structures. Length scale: 50 nm. c) A class average image of the cube highlights the four parallel layers building the basic shape. Because the cubes tend to lie on its sides, a differentiation between X and Y layers is not possible, consequently the class average is based on a mixture of X and Y layers standing perpendicular on the image plane. Length scale: 5 nm.