TEM images at higher magnification in Figures 2A, top confirm that isothermal assembly in TANa enables enough reconfigurability for the formation of distinct individual nanotubes while allowing their continuous growth over time up to micrometer length. When the same isothermal formation experiment was done in TAMg buffer, replacing NaCl with 12.5 mM MgCl 2 , nanotubes could still be detected in TEM images but were highly clustered in the form of micrometer-sized aggregates (Figure , bottom, Movie S2) that can be attributed to a stronger stabilization of the DNA nanostructures by divalent Mg 2+ cations.