Fig. 4.

(a) Formation of cell extract droplets with immersed MNBs (seen as tiny black rods) at a microfluidic T-junction. For the full time series see supplementary movie 2. (b) Rectangular region of interest in a cell extract microdroplet with fluorescently labeled microtubules, used for calculating $G(\tau )$ as presented in subfigure c (see supplementary movies 4 and 5 for the associated time series). (c) The average Pearson correlation coefficient, $G(\tau )$ (defined in Eq. (1)) shows a monotonous and featureless decay for image time series of fluorescently labeled microtubules in a cell extract (black circles). Upon stirring with MNBs (red squares), these supposedly thermal undulations are supplemented with an active noise, leading to an overall faster decay in $G(\tau )$, but with oscillatory-like features that reflect the nearby MNBs’ tumbling motion.