Fig. 2: DNA nanotubes and unregulated DNA nanotube growth.

a Left: DNA monomers are composed of five DNA strands folded into rigid double crossover structures⁶⁴. Right: Two monomer types co-assemble to form a cylindrical lattice via Watson–Crick hybridization of monomer sticky ends. b A DNA origami seed that presents monomer sticky ends at one edge (inset) acts as a stable nucleus from which nanotubes can grow without a significant energy barrier to nucleation. c At high monomer concentrations, spontaneous nanotube nucleation, growth, and joining all occur (regime I.). At intermediate monomer concentrations, DNA nanotubes nucleate and grow from seeds but spontaneous nucleation is rare (regime II.). The presence of a small energy barrier to nucleation from the seeds²³ results in a regime where growth from existing nanotubes is favorable but nucleation from additional seeds is rare (regime III.). At monomer concentrations below the critical concentation, no nanotube growth occurs (regime IV.). Fluorescence micrographs depict nanotubes (green) and seeds (red) after 24 h of growth at different initial monomer concentrations. Scale bars 10 µm. Supplementary Note 6 describes how the cutoffs for growth regimes were determined. d–f Results of experimental and simulated nanotube growth with 150 nM monomers at different seed concentrations (see “Methods” and Supplementary Note 4). d Mean lengths of seeded nanotubes measured in experiments (solid lines) and simulations (dashed lines). Error bars represent 95% confidence intervals from bootstrapping. e Fractions of viable seeds (Supplementary Note 7) that nucleated nanotubes after 72 h. Error bars on proportions represent 95% confidence intervals. The sample sizes (at least 50 nanotubes and seeds) for every timepoint of each sample are tabulated in Supplementary Note 14. f Free S monomer concentrations during simulations of growth. Shaded regions correspond to the growth regimes in c. Ideal regulation results in d–f are from simulations of nanotube growth without monomer depletion.