Abstract
Here we present an approach to measure dynamic membrane properties of phospholipid membranes close to an interface. As an example we show results of the membrane dynamics of a phospholipid membrane multilayer-stack on a solid substrate (silicon). On this sample we were able to measure local interaction and friction parameters using Grazing Incidence Neutron Spin Echo Spectroscopy (GINSES), where an evanescent neutron wave probes the fluctuations close to a rigid interface. With this method it is possible to access length scales in the nano to micrometer region as well as energies in the μeV range. Using a new neutron resonator structure we achieved the required intensity gain for this experiment. During our investigations we found an excitation mode of the phospholipid membrane that has not been reported previously and only became visible using the new methodology. We speculate that the energy transported by that undulation can also serve to distribute energy over a larger area of the membrane, stabilizing it. This new methodology has the capability to probe the viscoelastic effects of biological membranes, becoming a new tool for tribology on the nanoscale and has allowed the observation of the hitherto invisible property of phospholipid membranes using neutrons.
Highlights
Background considerationsIncoherent background scattering in this experiment can be accounted for in two ways: hydrogen in the phospholipid itself as well as the incoherent contribution from the solvent D2O.Since the interface region contains a significant amount of hydrogen, is confined in the membrane, it will reduce the polarization of the echo measurement as well as for the elastic polarization measurement
D2O prepared on a silicon substrate. The structure of this system has been studied before using neutron grazing incidence small angle scattering (GISANS) and reflectometry[20]
All modes observed here occur at solid-liquid interfaces, where a membrane is parallel and in close proximity to a solid substrate
Summary
Background considerationsIncoherent background scattering in this experiment can be accounted for in two ways: hydrogen in the phospholipid itself as well as the incoherent contribution from the solvent D2O.Since the interface region contains a significant amount of hydrogen (within the phospholipid layer), is confined in the membrane, it will reduce the polarization of the echo measurement as well as for the elastic polarization measurement. Incoherent background scattering in this experiment can be accounted for in two ways: hydrogen in the phospholipid itself as well as the incoherent contribution from the solvent D2O. Long wavelength undulations cannot be observed with the incoherent part of the scattering, since it represents only the self-correlation function, not the pair-correlation function. This part has been included as a static incoherent contribution in the model, which only accounts for the hydrogen in the phospholipid itself. The incoherent contribution from the solvent D2O seems to be slightly higher than expected compared to the phospholipid layer contribution, which might stem from some residual protonated solvent molecules from the sample preparation process
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