The underappreciated role of nonspecific interactions in the crystallization of DNA-coated colloids

TL;DR

This paper demonstrates that nonspecific interactions significantly influence the crystal structures formed by DNA-coated colloids, challenging the focus solely on specific DNA interactions in programmable self-assembly.

Contribution

It reveals the crucial role of nonspecific forces in determining colloidal crystal polymorphs and provides a combined experimental, simulation, and theoretical analysis.

Findings

Nonspecific interactions can lead to various binary crystal structures.

Simulations match experimental results quantitatively.

A theoretical model explains the balance of forces shaping crystal stability.

Abstract

Over the last decade, the field of programmable self-assembly has seen an explosion in the diversity of crystal lattices that can be synthesized from DNA-coated colloidal nanometer- and micrometer-scale particles. The prevailing wisdom has been that a particular crystal structure can be targeted by designing the DNA-mediated interactions, to enforce binding between specific particle pairs, and the particle diameters, to control the packing of the various species. In this article, we show that other ubiquitous nonspecific interactions can play equally important roles in determining the relative stability of different crystal polymorphs and therefore what crystal structure is most likely to form in an experiment. For a binary mixture of same-sized DNA-coated colloidal micrometer-scale particles, we show how changing the magnitudes of nonspecific steric and van der Waals interactions gives rise to a family of binary body-centered tetragonal crystals, including both cesium-chloride and copper-gold crystals. Simulations using pair potentials that account for these interactions reproduce our experimental observations quantitatively, and a theoretical model reveals how a subtle balance between specific and nonspecific forces determines the equilibrium crystal structure. These results highlight the importance of accounting for nonspecific interactions in the crystal-engineering design process.