10.1021/la0534219.s005 Chiaki Yoshina-Ishii Chiaki Yoshina-Ishii Yee-Hung M. Chan Yee-Hung M. Chan Joseph M. Johnson Joseph M. Johnson Li A. Kung Li A. Kung Peter Lenz Peter Lenz Steven G. Boxer Steven G. Boxer Diffusive Dynamics of Vesicles Tethered to a Fluid Supported Bilayer by Single-Particle Tracking American Chemical Society 2006 diffusive dynamics bulk medium Monte Carlo simulations vesicle diffusion Diffusive Dynamics surface defects lipid bilayer reversibly trap vesicle size depletion effect DNA hybridization membrane surface Vesicles Tethered diffusion behavior 200 nm phospholipid vesicles diffusion coefficient time scale 2006-06-20 00:00:00 Media https://acs.figshare.com/articles/media/Diffusive_Dynamics_of_Vesicles_Tethered_to_a_Fluid_Supported_Bilayer_by_Single_Particle_Tracking/3075292 We recently introduced a method to tether intact phospholipid vesicles onto a fluid supported lipid bilayer using DNA hybridization (Yoshina-Ishii, C.; Miller, G. P.; Kraft, M. L; Kool, E. T.; Boxer, S. G. <i>J. Am. Chem. Soc.</i> <b>2005</b>, <i>127</i>, 1356−1357). Once tethered, the vesicles can diffuse in two dimensions parallel to the supported membrane surface. The average diffusion coefficient, <i>D</i>, is typically 0.2 μm<sup>2</sup>/s; this is 3−5 times smaller than for individual lipid or DNA-lipid conjugate diffusion in supported bilayers. In this article, we investigate the origin of this difference in the diffusive dynamics of tethered vesicles by single-particle tracking under collision-free conditions. <i>D</i> is insensitive to tethered vesicle size from 30 to 200 nm, as well as a 3-fold change in the viscosity of the bulk medium. The addition of macromolecules such as poly(ethylene glycol) reversibly stops the motion of tethered vesicles without causing the exchange of lipids between the tethered vesicle and supported bilayer. This is explained as a depletion effect at the interface between tethered vesicles and the supported bilayer. Ca ions lead to transient vesicle−vesicle interactions when tethered vesicles contain negatively charged lipids, and vesicle diffusion is greatly reduced upon Ca ion addition when negatively charged lipids are present both in the supported bilayer and tethered vesicles. Both effects are interesting in their own right, and they also suggest that tethered vesicle-supported bilayer interactions are possible; this may be the origin of the reduction in <i>D</i> for tethered vesicles. In addition, the effects of surface defects that reversibly trap diffusing vesicles are modeled by Monte Carlo simulations. This shows that a significant reduction in <i>D</i> can be observed while maintaining normal diffusion behavior on the time scale of our experiments.