Sodium dodecyl sulfate is an anionic detergent commonly used to disrupt cell membranes.  The interaction of planar supported lipid bilayers with SDS at low concentrations (well below the critical micelle concentration) has been studied by total internal reflection (TIR) Raman scattering and fluorescence microscopy.  TIR Raman scattering uses the evanescent wave at the solid-water interface with a sampling depth of ~100 nm.  Deuterated SDS is used to distinguish the detergent from the lipids: the C-D stretching vibrations of the detergent are in the vicinity of 2200 cm<sup>-1</sup> while the C-H stretching bands of the lipid are around 2900 cm<sup>-1</sup>.  Upon exposure of a bilayers of a variety of different lipids to SDS, the detergent is incorporated into the bilayer and the intensity of the lipid peaks decreases, indicating a decrease in the number of lipid molecules within the evanescent wave.  Upon rinsing with pure buffer solution, the detergent peaks disappear and the lipid peaks recover.  The explanation for these changes can be understood from fluorescence microscopy of the lipid bilayers incorporating a red fluorescent dye. Addition of SDS causes the growth of tubules from the bilayer, up to several hundred microns long.  Given that the penetration depth of the evanescent wave is only ~100 nm, the lipid in these tubules is not sampled by TIR Raman scattering but remains attached to the surface.  Upon rinsing with buffer, the tubules retract and the lipid is reincorporated (at least in part) into the bilayer, explaining the recovery in the TIR Raman signal from the lipid.  TIR-Raman scattering provides addtional information about the phase and composition of the lipid bilayer that is not obtained from the fluorescence images. Fluorescence microscopy is more sensitive to the morphology of the layers.

Tubule formation and retraction in the interaction of supported lipid bilayers with SDS

253rd National Meeting (2017)

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