Lamellipod Reconstruction by Three-Dimensional Reflection Interference Contrast Nanoscopy (3D-RICN)
Abstract
There are very few techniques to reconstruct the shape of a cell at nanometric resolution and those that exist are almost exclusively based on uorescence, implying limitations due to staining constraints and artefacts. Reection Interference Contrast Microscopy (RICM), a label-free technique, permits measurement of nanometric distances between refrac-tive objects. However, its quantitative application to cells has been largely limited due to the complex interferometric pattern caused by multiple reections on internal or thin structures like lamellipodia. Here we introduce three dimensional reection interference contrast nanoscopy, 3D-RICN, which combines information from multiple illumination wavelengths and aperture angles to characterize the lamellipodial region of an adherent cell in terms of its distance from the surface and its thickness. We validate this new method by comparing data obtained on xed cells imaged with Atomic Force Microscopy and Quantitative Phase Imaging. We show that as expected, cells adhering to micropatterns exhibit a radial symmetry for the lamellipo-dial thickness. We demonstrate that the substrate-lamellipod distance may be as high as 100 nm. We also show how the method applies to living cells, opening the way for label-free dynamical study of cell structures with nanometric resolution.
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