DNA-mediated nanoparticle crystallization into Wulff polyhedra

Very slow cooling, over several days, of solutions of complementary-DNA-modified nanoparticles through the melting temperature of the system produces nanoparticle assemblies with the Wulff equilibrium crystal structure, thus showing that DNA hybridization can direct nanoparticle assembly along a pathway that mimics atomic crystallization. Slow route to crystals The crystallization processes of nanoparticles are far more complicated — and less well understood — than those of atoms. Chad Mirkin and colleagues now show that despite the presence of charged biomolecules and huge interparticle distances, DNA-mediated assembly of nanoparticles can follow a pathway that mimics atomic crystallization: very slow cooling, over several days, of solutions of DNA-modified nanoparticles below the melting temperature of the system produces single crystals with the expected equilibrium structure. The finding suggests that DNA-mediated assembly of this type is an ideal system for the study of complex crystallization phenomena, and for exploiting well-defined rules to target nanoparticle crystals with desired lattice symmetries and lattice constants. This approach has the potential to create single microcrystals with useful properties that may find practical applications in photonics and catalysis. Crystallization is a fundamental and ubiquitous process much studied over the centuries. But although the crystallization of atoms is fairly well understood 1 , 2 , it remains challenging to predict reliably the outcome of molecular crystallization processes that are complicated by various molecular interactions and solvent involvement. This difficulty also applies to nanoparticles: high-quality three-dimensional crystals 3 , 4 , 5 , 6 are mostly produced using drying and sedimentation techniques that are often impossible to rationalize and control to give a desired crystal symmetry, lattice spacing and habit (crystal shape). In principle, DNA-mediated assembly of nanoparticles offers an ideal opportunity for studying nanoparticle crystallization 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 : a well-defined set of rules have been developed to target desired lattice symmetries and lattice constants 8 , 9 , 18 , and the occurrence of features such as grain boundaries and twinning in DNA superlattices and traditional crystals comprised of molecular or atomic building blocks suggests that similar principles govern their crystallization. But the presence of charged biomolecules, i