Fig. 2

a Schematic of the setup for laser tracking of nanoparticles in vivo: the laser beam (1064 nm, red line) is focused in the embryo (inset) and the forward-scattered light is collected by a condenser and imaged onto a quadrant photodiode (QPD). In all optical trapping experiments, the immobilized zebrafish were mounted dorsolaterally in agarose on a microscope slide with the liver bud facing the objective. b Examples of positional power spectra of optically trapped particles in water (black, α = 0.97) or in a zebrafish embryo (blue, α = 0.77). The straight lines show fits of Eq. (1) to data. The inset shows the trajectories of a trapped (red) and a freely diffusing (black) particle in the foregut region of a living zebrafish embryo. c Power spectra of optically trapped nanoparticles in liver (green) or gut progenitors (blue). Full lines show linear fits to the double logarithmic plot in the frequency interval 400 Hz < f < 4000 Hz, yielding scaling exponents of 0.56 ± 0.08 (gut) and 0.76 ± 0.06 (liver), respectively. d Symbols (blue and green) provide the storage moduli, G’, of the gut and liver, same colors as in (c) and (d). The corresponding loss moduli, G”, are shown with dashed lines for comparison of the amplitude. G” dominates G’ over the 400–4000 Hz frequency interval for both tissue types. The full lines show fits to the loss moduli data in the corresponding region to the power spectra (c), returning scaling exponents of 0.53 ± 04 (gut) and 0.74 ± 0.05 (liver). The data shown in (c, d) is an average of five experiments for each cell type.