Regulating DNA Self-Assembly Dynamics with Controlled Nucleation.

Controlling the nucleation step of a self-assembly system is essential for engineering structural complexity and dynamic behaviors. Here, we design a "frame-filling" model system that comprises one type of self-complementary DNA tile and a hosting DNA origami frame to investigate the inherent dynamics of three general nucleation modes in nucleated self-assembly: unseeded, facet, and seeded nucleation. Guided by kinetic simulation, which suggested an optimal temperature range to differentiate the individual nucleation modes, and complemented by single-molecule observations, the transition of tiles from a metastable, monomeric state to a stable, polymerized state through the three nucleation pathways was monitored by Mg2+-triggered kinetic measurements. The temperature-dependent kinetics for all three nucleation modes were correlated by a "nucleation-growth" model, which quantified the tendency of nucleation using an empirical nucleation number. Moreover, taking advantage of the temperature dependence of nucleation, tile assembly can be regulated externally by the hosting frame. An ultraviolet (UV)-responsive trigger was integrated into the frame to simultaneously control "when" and "where" nucleation started. Our results reveal the dynamic mechanisms of the distinct nucleation modes in DNA tile-based self-assembly and provide a general strategy for controlling the self-assembly process.