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BP: Fachverband Biologische Physik

BP 10: Poster III

BP 10.19: Poster

Montag, 16. März 2020, 17:30–19:30, P2/3OG

What thermal fluctuations of an optically trapped bead can tell us about the properties of an interface — •Tetiana Udod, Felix Jünger, and Alexander Rohrbach — Lab for Bio- and Nano-Photonics, IMTEK, University of Freiburg, Georges-Koehler-Allee 102, 79110 Freiburg, Germany

Thermal position fluctuations of optically trapped beads can be measured in 3D with nanometer precision at MHz rates with back focal plane interferometry. The bead fluctuations change in amplitude and time upon interaction with interfaces, which can be characterized by different surface potentials or viscosities. Bead position fluctuations encode the hydrodynamic momentum transfer and repulsion at plane glass coverslips, giant unilamellar vesicles or even living cells, with complex and dynamic surface structures. However, defining and determining the contact between the fluctuating bead and an interface is far from trivial. When studying particle binding and induction of the phagocytic uptake pathway, the following question is of particular interest: When does a cell start to feel an approaching particle? To better understand such processes taking place on very small length and time scales, we first analyze the position fluctuation at simplified interface systems. Therefore, we use combination of experiments with Photonic Force Microscopy, Brownian Dynamic simulation and analytical theory to model and explain the impact of surface potentials and viscosities on the 3D bead position fluctuations. This allows us to identify the contact point and thereby to measure distance -dependent interactions even of living cells.