Diverse Colloidal Crystals and Clusters Formed by DNA-Grafted Spheres via Self-assembly

Meta-materials with novel photonic, phononic, thermal, and mechanical properties are considered as future materials for new applications. Colloidal crystals are meta-materials made from assemblies of building blocks that are not found in naturally occurring materials. Unlike atoms and molecules, such building blocks could be obtained from DNA-coated colloids which have feasible and adjustable interaction strengths as well as facilitating a further DNA-induced self-assembly into different geometries and structures. This DNA colloidal self-assembly prototyping process could be utilized as a fast and effective way for fabricating different structures, which shed light on the industrial production of the meta-materials. In this work, an extensive number of colloidal building blocks and crystal structures were obtained by our lab. Specifically, first, a swelling/de-swelling based method invented by our lab allowed us to attach F-108 tri-block polymers with DNA strands on ends onto polystyrene (PS) colloids with a high DNA concentration. This method was later updated and combined with a SPAAC based method so that a PS-PEO bi-block polymer with DNA strands on PEO end could also be attached onto PS colloids, yet with a lower cost and higher efficiency. Second, these DNA-coated colloids were mixed and crystallized through a slowly quenching system, which ultimately yielded colloidal crystals with high crystallinity. In total ten types of crystal structures were discovered, and six of them have never been reported before in the field. What more intriguing is we also observed the transformations from a mother phase into multiple child phases with the conclusion that ten structures are basically from two origins. It is worthwhile to mention that a double diamond structure was discovered. We believe its intersected two diamond packing unit made it advantageous in optical properties over other structures. Third, colloidal clusters with octahedral, tetrahedral, icosahedral, and cubic symmetries were also obtained by applying a co-crystallization method and ligating impurity particles within the crystals. The yielded clusters will be used to build up second-order structures. Another important discovery but without DNA involved was we were able to produce anisotropic tetrahedral and cubic 3-methacryloxypropyl-trimethoxysilane (TPM) particles, which could be used in gravity-induced self-assembly