Figure 1: Dependency of unidirectional FF nanotube elongation and shortening on free monomer concentration.

(a) Crystalline conformation of an FF monomer. (b) Architecture of the microfluidic device. Two inlets, followed by a long and narrow mixing channel and a wider channel with micro-scale pillars. (c) Nanotube illustration. (d) The narrow mixing channel ensures the two solutions are mixed properly, as demonstrated with yellow and blue food colouring solutions. (e) Illustration of a nanotube confined by the micro-scale pillars. (f–h) Illustration and imaging of FF nanotubes. A series of seven images at different time points under supercritical (3.20 mM) (100 s interval between images) (f) critical (2.43 mM) (60 s interval between images) (g) and subcritical (1.60 mM) (10 s interval between images) (h) concentrations. Supercritical concentration resulted in the elongation of the nanotubes. At the critical concentration, the assembly and disassembly rates are equal. The length of the same nanotube at a subcritical concentration decreases due to the reduced assembly rate. Scale bars, 5 μm.