Hierarchical Assembly and Dynamic Transitions of DNA-Coated Colloids

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NONTECHNICAL ABSTRACTColloids--microscopic bits of matter dispersed in a fluid--are powerful model systems for studying phenomena in condensed matter physics, as well as promising building blocks for nanomaterials. Like atoms, they form bulk phases of matter such as gases and crystals. But unlike atoms, colloidal particles can be encoded with information that can be used to tell them how to assemble into useful structures. The ultimate goal of this project is to improve methods for directing, or programming, colloidal self-assembly by relating the information stored in particles to the assembly pathways and complex structures that emerge. The research team uses DNA sequences grafted to colloidal particles, together with other DNA sequences dissolved in solution, to control interactions between particles, and investigates how these particles assemble to form various structures. The results could prove especially useful in nanotechnology, where a central goal is to manufacture materials and devices by growing them directly from solution. The research trains doctoral and undergraduate students in the emerging, interdisciplinary field of programmable self-assembly, and educates roughly 120 undergraduate students in the life sciences per year through engaging, open-ended labs focused on applying introductory physics concepts to problems in biology.TECHNICAL ABSTRACTDNA-coated colloids can assemble into interesting structures and phases, and are one of the most promising experimental systems for studying phase transitions and self-assembly in soft condensed matter. This experimental project investigates and advances an underexplored paradigm, in which colloids interact by free DNA strands in solution instead of direct binding of grafted strands, and elucidates the fundamental rules governing assembly in such systems. The principle investigator's research team takes a hierarchical approach, studying quantitatively the entire flow of information from the molecular scale to interactions at the colloidal scale, and then from the colloidal interactions to the phase behavior that emerges at the system scale. The central questions being addressed are: how does the emergent phase behavior depend on details of the pair interaction, and how does the pair interaction in turn depend on the attributes of DNA strands dissolved in solution? To answer these questions, the research team uses a variety of modern optical techniques, including optical microscopy, total internal reflection microscopy, and differential dynamic microscopy, and develops quantitative models to interpret and unite their observations. Understanding how DNA sequences are compiled into structure and function is essential to the ultimate goals of engineering and manufacturing materials from the bottom up. The project will train doctoral and undergraduate students in soft matter physics and applied optics, and educate undergraduates in the life sciences through a series of inquiry-based labs using optical microscopy.