Universal pH-Responsive and Metal-Ion-Free Self-Assembly of DNA Nanostructures.

pH-responsiveness has been widely pursued in dynamic DNA nanotechnology, owing to its potential in biosensing, controlled release, and nanomachinery. pH-triggering systems mostly depend on specific designs of DNA sequences. However, sequence-independent regulation could provide a more general tool to achieve pH-responsive DNA assembly, which has yet to be developed. Herein, we propose a mechanism for dynamic DNA assembly by utilizing ethylenediamine (EN) as a reversibly chargeable (via protonation) molecule to overcome electrostatic repulsions. This strategy provides a universal pH-responsivity for DNA assembly since the regulation originates from externally co-existing EN rather than specific DNA sequences. Furthermore, it endows structural DNA nanotechnology with the benefits of a metal-ion-free environment including nuclease resistance. The concept could in principle be expanded to other organic molecules which may bring unique controls to dynamic DNA assembly.