Physics (Internal)

Nanoscale cell membrane fluctuations quantified by optical interferometry

This event is part of the Biophysics/Condensed Matter Seminar Series.

Red blood cells (RBCs) must withstand large deformations during multiple passages through microvasculature. This essential ability is diminished with age and disease. Therefore, quantifying the mechanical properties of live RBC membranes provides insight into a variety of problems regarding the interplay of cell structure, dynamics, and function. RBC thermal fluctuations (“flickering”) have been studied for more than a century as they offer a potential window into these phenomena. Nevertheless, quantifying these motions is experimentally challenging, as they develop at the nanometer and millisecond scales across the entire cell. Thus, reliable spatial and temporal data are currently limitted. Here we use diffraction phase microscopy, a novel, highly sensitive optical imaging technique, to quantify the flickering of RBC membranes. This method relies on quantifying with sub-nanometer accuracy the optical path-length shift associated with the light passing through the cell. The static (spatial) behavior of the membrane displacements allow for the first time extracting the effective membrane tension, which is modulated by the cell cytoskeleton. The dynamic analysis reveals significant properties of both temporal and spatial correlations of the membrane motions. We show that these correlations can be accounted for by the viscoelastic properties of the cell membrane, which strongly correlated with cell morphology. We believe that this type of investigation promises to provide a better understanding of diseases such as malaria and sickle cell anemia. Furthermore, understanding the RBC membrane behavior will be important in studying the membrane of other cell types, for which RBCs are convenient models.