Diffusion of colloids in an active enzyme bath

The diffusion of microscopic particles suspended in a fluid due to random thermal fluctuations in the surrounding environment is a manifestation of Brownian motion. It has been hypothesized that these particles can experience enhanced diffusion if catalysis of an enzyme-substrate reaction is included in the fluid bath. Using differential dynamic microscopy we look to extract the dynamics of colloidal suspensions in the presence of enzyme activity, specifically a urea-urease reaction, and verify enhanced diffusion when compared to colloids in a bath with no activity. In order to verify the activity and timescale of our enzyme bath we use a phenol red assay to measure the change in absorbance over time at the 560nm wavelength, which indicates enzymatic activity through a pH change. Preliminary results suggest that our urea-urease enzyme bath is active and Brownian-like diffusion of colloids can be characterized via differential dynamic microscopy. We investigate the dependence of passive colloid size on diffusion enhancement due to enzyme bath activity. These experiments set the stage for using active baths to drive transport of passive objects.