The reversibility of DNA condensation led us to explore if the nanotube superstructures could be disassembled after their formation. It is known that adding an excess of monovalent cations on condensed DNA can compete with the DNA neutralization by multivalent counter-ions leading to DNA decompaction. Following this principle, nanotubes were first assembled into networks by introducing [SPM 4+ ] = 0.4 mM prior to adding NaCl (100 mM) to the solution. Notably, right after Na + addition, nanotubes were observed freely fluctuating in solution in a state comparable to that before spermine introduction (Fig. , Movie S2). To achieve further control with an external stimulus without having to change the chemical composition of the medium, we implemented AzoTAB, a photosensitive DNA condensing agent. AzoTAB is a cationic amphiphilic molecule neutralizing DNA in a photodependent manner, the trans isomer inducing DNA condensation at a lower concentration than the cis isomer. We used an AzoTAB solution kept in the dark (-UV, trans-rich state) or irradiated at 365 nm for 1 min (+UV, cis-rich state). Starting from individual nanotubes obtained by thermal annealing in TAMg buffer, we added different amounts of AzoTAB, without or with UV, and analyzed the resulting assemblies (Fig. ). Regardless of irradiation conditions, nanotubes at a low concentration of AzoTAB (0.1 mM) were freely fluctuating in solution and appeared similar to nanotubes without AzoTAB (Figs. S8, 1B left, and Movie S1). Without UV, increasing AzoTAB concentration to 0.5 and 1 mM led to the formation of clustered nanotube assemblies presenting some similarities with the networks obtained with multivalent cations. Notably, with UV, nanotubes remained individual at