Measuring crystal nucleation and growth of DNA-grafted colloidal particles

Grafting DNA onto microscopic colloidal particles can `program' them with information that tells them how to self-assemble into a variety of interesting crystal structures. However, the dynamic pathways by which these crystals self-assemble are largely unknown. In this talk I will present progress on an experimental study of the nucleation and growth of colloidal crystals due to DNA hybridization. Specifically, I will describe a microfluidics-based approach in which we produce hundreds of monodisperse, isolated droplets filled with colloidal particles and then track the formation of crystals within each drop as a function of time. We find that the initial nucleation of crystals from a supersaturated solution involves overcoming a free-energy barrier, and that the height of this barrier decreases dramatically with decreasing temperature. We also find that once nucleated, the crystals grow at a rate that is limited by the diffusive flux of colloidal particles to the growing crystal surface. These findings may help us to devise strategies to tune the nucleation rates and crystal growth kinetics independently, which will be helpful as we try to engineer higher quality or more complex self-assembled structures.