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Lateral diffusion of a submicron particle on a lipid bilayer membrane Kazuki Shigyou, Ken H Nagai, and Tsutomu Hamada Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b02448 • Publication Date (Web): 25 Oct 2016 Downloaded from http://pubs.acs.org on October 26, 2016
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Lateral diffusion of a submicron particle on a lipid
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bilayer membrane 1
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Kazuki Shigyou, 1Ken H. Nagai, 1Tsutomu Hamada.*
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Ishikawa 923-1292 Japan.
Japan Advanced Institute of Science and Technology, School of Materials Science, 1-1 Asahidai, Nomi,
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ABSTRACT
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In the past decades, nanoparticles and nanomaterials have been actively used for
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applications such as visualizing nano/submicron cell structure, killing cancer cells and drug
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delivery systems. It is important to understand the physicochemical mechanisms that govern the
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motion of nanoparticles on a plasma membrane surface. However, the motion of small particles
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of < 1000 nm on lipid membranes is poorly understood. In this study, we investigated the
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diffusion of particles with a diameter of 200~800nm on a lipid membrane using cell-sized
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liposomes. Particle-associated liposomes were obtained by applying centrifugal force to a
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mixture of liposome and particle solutions. We measured the thermal motion of the particles by
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phase-contrast microscopy. We found that i) the particle-size-dependence of the diffusion of
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particles adhering to membranes was better described by the DADL model rather than the
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Einstein-Stokes model, ii) the diffusion coefficient of a particle highly depends on the adsorption
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state of the particle, such as fully or partially wrapped by the membrane, and iii) anomalous
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diffusion was induced due to the localization of particles on the neck of budded vesicles.
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Introduction
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It is important to understand the physicochemical mechanisms that govern the
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movements of molecules on a plasma membrane surface1. Since a plasma membrane is a
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two-dimensional fluid, membrane-associated molecules exhibit dynamical motion under the
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viscosity of the membrane2. Cells use membrane proteins diffusing on the membrane surface to
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regulate the traffic of molecules between their interior and exterior through osmosis, ion channel,
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endocytosis, exocytosis and phagocytosis. Endocytic and exotic deformations are induced by the
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aggregated movement of clathrin proteins that receive signal molecules on the living cell
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membrane3. Assembled actin filaments induce membrane deformation of phagocytosis4. Control
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of the motion of proteins diffusing on the membrane would lead to developing the regulation of
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physiological functions.
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There are two main methods by which the motion of objects on the membrane are
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controlled. First, molecules regulate membrane components, such as membrane lipids and
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cytoskeletal proteins that reinforce the membrane surface. Modulation of the membrane
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components changes the membrane fluidity5. Second, materials can be controlled using external
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stimuli. Over the past decades, researchers in the fields of nanoscience and nanotechnology have
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focused on developing methods for the application of nano/micro-particles to biological systems.
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For example, the motion of self-propelled6 particles can be controlled by light, and gold
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nanorods show photothermal effects by surface plasmon resonance7, which leads to a change in
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membrane fluidity and it motion by local heating. In other words, the particle movements and
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thermal effects can change a membrane condition, such as cytoskeleton networks and lipid
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fluidity. These possibly lead to a control of proteins that diffuse and organize on the membranes.
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To control the diffusion of objects on cell membranes with the use of nano/micro
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particles, we should consider two processes: i) the adhesion and localization of particles on a
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lipid bilayer. and ii) dynamical motion of the particles after adhesion. Recently, experiments with
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a model membrane, such as cell-sized liposomes, and theoretical models together with numerical
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simulations have been developed to clarify the physico-chemical mechanisms of biological
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events in cell membranes8,9,10,1112. Deserno et al. theoretically studied the adhesion stability of
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particles within a soft membrane.13–15 They proposed an equilibrium phase diagram, including
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particles wrapped by the membrane, in terms of the free energy of the membrane as a function of
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adhesion energy, liposome size, membrane tension and excess surface area of the liposome. In
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addition, computational and theoretical studies on particles adhered on cell membranes have
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been performed to better understand cellular uptake12,15–17. Along these lines, Hamada et al.
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investigated the localization of particles on phase-separated model membranes18. Small particles
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with a diameter of 1000 nm23,24. For practical applications to
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living cells, particles of
