Circular DNA exhibits non-monotonic changes in diffusivity during active topological conversion*

Active soft materials have been widely investigated in recent years. However, using polymer topology as a route to actively alter the viscoelastic properties of a material remains largely unexplored. Here, we confer non-equilibrium dynamics into complex fluids by using enzymes to alter the topology and size of concentrated DNA molecules. We incorporate restriction endonucleases into concentrated solutions of supercoiled DNA to linearize, fragment, and concatenate the molecules over time. We image labeled DNA within the solutions and use differential dynamic microscopy (DDM) to measure the time-varying ensemble dynamics of the DNA molecules during enzymatic activity. Our results show that during enzymatic digestion, DNA diffusion rates display a complex non-monotonic dependence on time, with noise arising from large non-equilibrium fluctuations in the distribution of DNA topologies. These active dynamics - tunable by enzyme and DNA concentration - arise from the changing topology and size of the DNA molecules and the nature of their entanglements with surrounding molecules.