Membrane ripples of a living cell measured by non-interferometric widefield optical profilometry

We measured the membrane topography and dynamics on a living fibroblast by using the non-interferometric widefield optical profilometry (NIWOP) technique. With a water-immersion objective of a 0.75 numerical aperture, our NIWOP system provides depth resolution about 20 nm. The imaging speed could be as high as 5 frames/min. We directly observed and profiled the inward propagation of membrane ripples near the cell edge. To verify if the membrane activity was driven by the underlying cytoskeleton, we changed the structure of the cell cortex while observing the membrane topography. After dissolving the actin cortex by cytochalasin D, we found that the propagation of the membrane ripples disappeared and the edge of the cell shank. The non-contact NIWOP technique does not affect the motility and viability of cells and therefore is suitable for the studies on cell physiology related to membrane motions.