Rotational optical tweezers for active microrheometry within living cells

Studying the mechanical properties of living cells provides opportunities to unravel the physical phenomena that govern biological functions. Macropinocytosis is a cellular pathway that involves the non-selective uptake of extracellular fluid through the formation of a macropinosome and is implicated in crucial cell-specific roles. Here, we describe an in vivo intracellular study that exploits a high-resolution rotational geometry to trap and monitor a photonic probe within a macropinosome. We use the transfer of spin angular momentum in rotational optical tweezers and show that active microrheometry methods can be successfully conducted in vivo, leading to a shear viscosity measurement of a macropinosome lumen within a living cell of (1.01 +/- 0.16) mPa s. This work provides a foundation for dynamic mechanobiological studies characterizing biological processes of intracellular vesicles. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement