pH-Responsive Nanoparticle Superlattices with Tunable DNA Bonds

Stimuli-responsive nanomaterials with re-configurable structures and properties have garnered significant interest in the fields of optics, electronics, magnetics, and therapeutics. DNA is a powerful and versatile building material that provides programmable structural and dynamic properties, and indeed, sequence dependent changes in DNA have already been exploited in creating switchable DNA-based architectures. However, rather than designing a new DNA input sequence for each intended dynamic change, it would be useful to have one simple, generalized stimulus design that could provide multiple different structural outputs. In pursuit of this goal, we have designed, synthesized, and characterized pH dependent, switchable nanoparticle superlattices by utilizing i-motif DNA structures as pH-sensitive DNA bonds. When the pH of the solution containing such superlattices is changed, the superlattices reversibly undergo: (i) a lattice expansion or contraction, a consequence of the pH-induced change in DNA length, or (ii) a change in crystal symmetry, a consequence of both pH-induced DNA "bond breaking" and "bond forming" processes. The introduction of i-motifs in DNA colloidal crystal engineering marks a significant step toward being able to dynamically modulate crystalline architectures and propagate local molecular motion into global structural change via exogenous stimuli.