Force fluctuations in an active enzyme bath

Optical tweezers have allowed the quantitative study of piconewton-scale forces in many biological systems. An interesting recent example is active colloids constructed from urease attached to passive particles in a urea bath – which exhibit enhanced diffusion and measurably increased force fluctuations. In this study, we measure the force fluctuations of a physically different situation – a passive colloid (r=0.5um) immersed in an active enzyme bath composed of freely diffusing urease and urea. The concentration of urease is varied from 0-100U/mL. We find that despite the high concentration of urease, no enhanced force fluctuations are observed – perhaps due to the separation of length scales between the passive colloid and individual active enzymes. To test this, we decorate streptavidin-coated particles with a urease-biotin complex and measure their force fluctuations in a urea bath. These experiments set the stage for understanding the energetics of enzyme-propelled active matter.