Hierarchical Crystals Formed from DNA-Functionalized Janus Nanoparticles.

Harnessing anisotropic interactions in a DNA-mediated nanoparticle assembly holds great promise as a rational strategy to advance this important area. Here, using molecular dynamics simulations, we report the formation of novel hierarchical crystalline assemblies of Janus nanoparticles functionalized with two types of DNA chains (DNA-JNPs). We find that in addition to the primary nanoparticle crystallization into face-centered cubic (FCC) structure, sequence-specific DNA hybridization events further direct the rotational orientation of the DNA-JNPs to diverse secondary crystalline phases including simple cubic (SC), tetragonally ordered cylinder (P4), and lamella (L) structures, which are mapped in the phase diagrams relating to various asymmetric parameters. The crystallization dynamics of such hierarchical crystals is featured by two consequent processes: entropy-dominated translational order for the primary crystalline structure and enthalpy-dominated rotational order for the secondary crystalline structure. For DNA-JNPs with high asymmetry in DNA sequence length, tetrahedral nanoclusters tend to be favored, which is revealed to be governed by the conformational entropy penalty caused by bounded DNA chains. This work might bear important consequences for constructing new classes of nanoparticle crystals with designed structures and properties at multiple levels and in a predictable manner.