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BP: Fachverband Biologische Physik

BP 17: Poster Session II

BP 17.67: Poster

Dienstag, 18. März 2025, 18:00–20:30, P4

Measuring activity from particle trajectories — •Lukas Abegg, Till M. Muenker, and Timo Betz — Third Institute of Physics, Georg August Universität Göttingen, Göttingen, Germany

Is it possible to distinguish activity from thermal fluctuations just from observed trajectories? The newly introduced statistical quantity Mean Back Relaxation aims to achieve exactly this by using three-point correlation functions. This non-dimensional function yields a measure for deviation from equilibrium within a confined system. It is calculated as the average displacement of a tracer article under the condition of having moved the distance d in advance. For an equilibrium process, this quantity results in a long time value of 1/2. However, deviation from this value is a marker for broken detailed balance. To gain deeper insight into this new statistical measure, we investigate this quantity inside a controlled system, namely a viscoelastic polyacrylamide gel. This probe was tuned to imitate the mechanical properties of cells, containing polystyrene particles with a size of one micron. To drive this system out of equilibrium, we use a movable optical tweezer to simulate active motion of the particle. The Mean Back Relaxation is calculated for all trajectories and fitted with an analytical solution for a viscoelastic system. The results are used to quantify the diffusion coefficient of the trapping laser and thus, the activity of the system tuned by our experimental realisation. Additionally, we can calculate the shear modulus G^⋆ from this result.

Keywords: Optical tweezer; Rheology; Cell Mechanics