The Role of Repulsion in Colloidal Crystal Engineering with DNA

Hybridization interactions between DNA-functionalized nanoparticles (DNA-NPs) can be used to program the crystallization behavior of superlattices, yielding access to complex three-dimensional structures. Yet the role of repulsive interactions in guiding structure formation is still largely unexplored. Here, a comprehensive approach is taken to study the role of the DNA shell, enabling the calculation of interparticle interaction potentials based on experimental results. In this work, we used two different means to assemble DNA-NPs—Watson-Crick base-pairing interactions and depletion interactions—and systematically varied the salt concentration to study the effective interactions in DNA-NP superlattices. A comparison between the two systems allows us to decouple the repulsive forces from the attractive hybridization interactions that are sensitive to the ionic environment. To better understand such behavior, we propose a model that provides a mathematical description for repulsive interaction caused by the polyelectrolyte shell.