Movie S1.

Fluorescence movie (1 frame per s) of Cy3-labeled DNA nanotubes in a microfluidic channel (dashed lines, height 100 μm) under slow flow rate (right to left, 47 μm/s in the center). The nanotubes experience compressional and elongational flows as they enter and exit the side chamber, respectively. The maximum elongational flow in the channel was estimated to be 1.4 /s, which is, using a conformational relaxation time of 400 ms for the nanotubes, within a factor of 2 of the critical threshold for polymer stretching (33). The measured maximum elongational flow during the bursting of a bubble (SI Appendix, Fig. S1) is ∼ 108-fold larger than in the channel. Consequently, the elongational flow during the expansion of the bubble hole is expected to orient and stretch DNA nanotubes. Given that the longest observed nanotube in the movie is 52 μm, the maximum elongational-flow-induced tension in the channel was calculated to be 1.2 pN (Eq. 1). The maximum generated tension in the movie is more than two orders of magnitude smaller than the critical tension to break a 7-helix DNA nanotube (455 pN). The weak hydrodynamic-induced tension is sufficient to explain the absence of nanotube scission in the movie.