  Inertia does not generally affect the long-time diffusion of passive
overdamped particles in fluids. Yet a model starting from the Langevin equation
predicts a surprising property of particles coated with ligands, that bind
reversibly to surface receptors -- heavy particles diffuse more slowly than
light ones of the same size. We show this by simulation and by deriving an
analytic formula for the mass-dependent diffusion coefficient in the overdamped
limit. We estimate the magnitude of this effect for a range of biophysical
ligand-receptor systems, and find it is potentially observable for tailored
micronscale DNA-coated colloids.
