Ellipsometry and differential interference contrast microscopic imaging of cellular exo and endocytosis: modelling and experiments

In this work it is presented a solution to Maxwell’s equations for core-shell nanoparticle scattering near an isotropic substrate covered with an anisotropic thin film, based on an extension of the Bobbert-Vlieger (BV) solution for particle scattering near a substrate, delivering an exact solution in the near-field as well as far-field. It is applied successfully the developed scattering model to the calculation of light scattering on an optical model representing a lipid vesicle near a lipid bilayer, whereby the lipids are characterized through a uniaxial optical model. Hereby, it is paved the path for understanding quantitatively how light scatters during a cellular exo- or endocytosis event during microscopic observation taking into account lipid induced anisotropy. Through the application of ellipsometry angles it is effectively demonstrated that realistically small optical anisotropy values significantly alter far-field optical scattering in respect to an equivalent optical model for cellular endocytosis consisting of isotropic components only. It is then calculated the impact of lipid-induced optical anisotropy on the experimental observation of exo- or endocytic microscopic imaging with e.g. Differential Interference Contrast (DIC) microscopy. Furthermore, it is integrated this extended BV scattering solution into a rigorous model of DIC image formation which allows for characterizing DIC, through simulation, as a tool for imaging of exo- or endocytosis events. It is also compared theoretical predictions with experimental high Numerical Aperture (NA) dic imaging of dielectric oxide nanoparticles with organic shell.