(176d) A Cation-Driven Bioinspired Approach to Actuate DNA Bonds in Colloidal Crystals

DNA-functionalized nanoparticles can be assembled into hierarchical structures through complementary interactions of the DNA surface ligands. These constructs can be viewed as programmable atom equivalents in which, unlike atomic systems, the atom (nanoparticle core) and the bond (DNA) can be tuned independently. By controlling the nanoparticle size, shape, and composition as well as the DNA sequence, length, and density, a vast library of crystalline structures can be obtained. In this work, we have developed a strategy that allows the DNA bond length to be modified post-synthetically, allowing interparticle spacings to be altered dynamically, thus leading to a new class of tunable metamaterials.

Inspired by histone proteins that condense DNA within the nuclei of cells due to the interactions of the negatively charged DNA backbone with the multiple positive surface residues on the proteins, we investigated the ability of 10 different cations to actuate the DNA bonds in colloidal crystals. Our results show that cations with multiple charges alter DNA structure on the molecular scale, enabling the DNA bond length to be reversibly altered between 28 nm and 3 nm, ultimately leading to changes in the overall dimensions of the original micron-sized superlattice at sub-second timescales. The identity, charge, and concentration of the cations all control the extent of actuation, with Ni²⁺ capable of inducing a remarkable 80% reversible change in crystal volume. The addition of multivalent cations is accompanied by an increase in the “bond strength” which increases the thermal stability of the superlattices by >60 °C.

To gain insight into the conformational changes in the DNA structure associated with the actuation process, we performed molecular dynamics simulations. These studies show that cations that screen the negative charge on the DNA backbone more effectively cause greater crystal contraction. Taken together, the use of multivalent cations represents a powerful bioinspired strategy to alter superlattice structure and stability, which can impact diverse applications through dynamic control of material properties, including optical, magnetic, and mechanical properties.