Diffusion of DNA-coated colloids on DNA coated surface

DNA-coated colloids can self-assemble and crystalize into a wide variety of structures. In order for DNA-coated colloids to anneal and form crystals, they must roll and diffuse while attached to each other. Here we report on the diffusion of DNA-coated colloidal spheres on a flat DNA-coated substrate. Near the DNA-melting temperature, the mean square displacement is linear in time as expected for normal diffusion, but the diffusion coefficient is much smaller than for free diffusion. As the temperature is lowered, the motion becomes sub-diffusive, which suggests the presence of random free energy barriers in the DNA-mediated interactions. We have found that DNA induced interactions are highly sensitive to the density and homogeneity of the DNA distribution. As we reduce the DNA density, the DNA coated colloids diffuse slower. Here we also report the modeling of melting curve for particle - substrate binding, allowing to understand and predict how binding properties depend on parameters of the DNA-coated colloids (salt concentrations, DNA sequence, etc.) This study is important for designing and optimizing self-assembly structure of DNA coated colloids.