Optical tweezers microrheology integrating differential dynamic microscopy: coupling stress response to macromolecular strain fields

How local nonlinear stresses propagate through soft matter systems remains an important open question. Here, I present a powerful approach–Optical Tweezers integrating Differential Dynamic Microscopy (OpTiDDM)–that simultaneously imposes local strains, measures resistive forces, and analyzes the motion of the surrounding polymers. By coupling optical tweezers with fluorescence microscopy, we are able to precisely map the time-dependent deformation fields arising from local nonlinear straining in biopolymer networks and complex fluids. Specifically, we measure the stresses imposed in the fluids by local optically-driven strains, and simultaneously image labeled biopolymers surrounding the strain site. Using DDM, we characterize the macromolecular dynamics and deformation as a function of strain rate and distance from the applied strain. With its robust suite of capabilities, as well as its modular and adaptable design, we anticipate broad interdisciplinary use of OpTiDDM to elucidate non-trivial phenomena that dictate and are impacted by the propagation of local stresses through a system–critically important to commercial materials applications and cell mechanics alike.