Single-particle tracking data reveal anticorrelated fractional Brownian motion in crowded fluids.

Anomalous diffusion with a sublinear growth of the particles' mean-square displacement (subdiffusion) has been observed frequently in crowded fluids, e.g., in the cytoplasm of living cells or in artificial solutions. Based on a recently reported set of single-particle tracking data, it is shown here that trajectories of nanoparticles immersed in artificial crowded fluids display all signatures of anticorrelated fractional Brownian motion. Moreover, the trajectories' power spectrum follows a scaling that reports on the fluid's viscoelasticity. Macromolecular crowding therefore renders fluids viscoelastic which in turn leads to subdiffusion of immersed tracer particles with all the characteristics of fractional Brownian motion.