Translational and rotational diffusion of semiflexible DNA polymers and rod-like fd virus particles on weakly charged freestanding cationic lipid membranes

Diffusion and conformational dynamics of single semiflexible and flexible macromolecules and colloids adhereing to freestanding lipid membranes is a challenging problem both from the experimental and theoretical standpoint. Using cationic supergiant unilamellar vesicles [1] as an experimental platform for mimicking freestanding lipid membrane in combination with single-molecule fluorescence video microscopy, we have previously discovered that local interaction of single DNA molecules with moderately and strongly charged freestanding lipid membranes can lead to interesting unexpected effects [2]. In the present contribution, using the same experimental technique, we investigate the diffusion behavior of semiflexible DNA polymers and much more rigid negatively charged colloidal particles, fd viruses [3], upon their electrostatic binding to weakly charged freestanding cationic lipid membranes. The wide range of contour lengths of DNA macromolecules (5–48.5 kbp) and fd virus particles (0.88–9.7 μm), allowed us to observe the crossover from the stiff-rod to semiflexible (fd virus) and from semiflexible to flexible (DNA) behavior which is accompanied by a crossover in the diffusion behavior of membrane-attached particles – from the 2D membrane-controlled to 3D bulk fluid-controlled diffusion dynamics. We compare the obtained experimental results on translational and rotational diffusion of DNA and fd virus particles with the predictions of hydrodynamics-based theories of membrane diffusion [4–8] and determine their ranges of applicability.