One- and two-particle microrheology of soft materials based on optical-flow image analysis†‡

Particle-tracking microrheology probes the rheology of soft materials by accurately tracking an ensemble of embedded colloidal tracer particles. One-particle analysis, which focuses on the trajectory of individual tracers is ideal for homogeneous materials that do not interact with the particles. By contrast, the characterization of heterogeneous, micro-structured materials or those where particles interact directly with the medium requires a two-particle analysis that characterizes correlations between the trajectories of distinct particle pairs. Here, we propose an optical-flow image analysis as an alternative to the tracking-based algorithms to extract one and two-particle microrheology information from video microscopy images acquired using diverse imaging contrast modalities. This technique, termed optical-flow microrheology (OFM), represents a high-throughput, operator-free approach for the characterization of a broad range of soft materials, making microrheology accessible to a wider scientific community.