Fig. 3: 3D-SPT in human lung carcinoma (A549) cells by TEMPSI.

a Overlay of white light and fluorescence images of representative A549 cells with embedded beads. Six beads whose tracks are shown in (b) are numbered in Roman numerals. Color reflects imaging depths of ~2-μm and ~5-μm relative to the glass-cell interface (hot and green-pink colormaps, respectively). The beads at each depth were tracked simultaneously over 30 s at 25 3D localizations s⁻¹ with an average of ~35 × 10³ photons/localization. Scale bar, 5 μm. b 3D trajectories of the six beads numbered in Roman numerals in (a), where the trajectory color encodes time going from blue to red. c log–log MSD/τ curves of the trajectories in (b). The vertical axis shows the ratio of the mean square displacement to the lag time. Dots and squares are measurements and solid lines are fits. The curved convex lines (I and IV), the negative slope lines (II and V), and the slow slope curves straightened at longer lag times (III and VI) are characteristic of directed, subdiffusive, and diffusive motions in the cell microenvironment, respectively. d Histograms of the speed (v, left; n = 149 trajectories) and the exponent α (right; n = 104 trajectories) of the motion in the cell microenvironment. 59% of the trajectories showed directed motion (DM), whereas from the remaining 41% trajectories, 82% exhibited α < 1