Gauging nanoswimmer dynamics by tracking the motion of large bodies

Nanoscale swimmers such as enzymes and chemically powered nanomotors generated much interest as a fundamental physical phenomenon and for their potential in biomedical and technological applications. However, measuring nanoswimmers proved extremely challenging due to their minute size and the dominant effect of thermal fluctuations. To address this problem, we present a simple recipe to probe the elusive physical features of nanoswimmers by measuring their effect on easily traceable micron-size particles. Modeling the nanoswimmers as an ensemble of hydrodynamic force dipoles, we link the tracers' power spectrum and diffusion coefficient to the nano-swimmers basic properties, particularly their dipole moment and dynamical timescales.