Single-particle tracking: Brownian dynamics of viscoelastic materials

A unifying theoretical framework for analyzing stochastic data from single- particle tracking (SPT) in viscoelastic materials is presented. A generaliz ation of the bead-spring model for linear polymers is developed from a mole cular point of view and from the standpoint of phenomenological linear visc oelasticity. The hydrodynamic interaction in the former is identified as th e dashpots in the latter. In elementary terms, the intimate correspondence between time-correlation of the fluctuation measurements and transient rela xation kinetics after perturbation is discussed, and the central role of th e fluctuation-dissipation relation is emphasized. The work presented here p rovides a bridge between the microscopic and the macroscopic views of linea r viscoelastic biological materials, and is applicable to membrane protein diffusion, linear DNA chain dynamics, and mechanics of intracellular cytosk eletal networks.