Brillouin Spectroscopy of Binary Phospholipid-Cholesterol Bilayers

Area of Science:

• Biophysics
• Materials Science
• Spectroscopy

Background:

• Lipid rafts are crucial for biomembrane function, but their nanoscale organization is poorly understood.
• Multicomponent lipid bilayers serve as models to study biomembrane heterogeneities.
• Spatial organization of lipid bilayers at the hundred-nanometer scale remains a challenge to probe.

Purpose of the Study:

• To investigate the spatial organization and phase coexistence in multicomponent lipid bilayers.
• To explore the potential of Brillouin spectroscopy for studying nanoscale lipid bilayer structures.
• To analyze domain sizes and homogeneity in binary lipid mixtures.

Main Methods:

• Application of Brillouin spectroscopy to oriented planar multibilayers.
• Utilized three binary lipid mixtures: DOPC, DPPC, and cholesterol.
• Employed two scattering geometries to probe lateral and normal phonon propagation.

Main Results:

• Bimodal Brillouin peaks observed in DPPC-DOPC mixtures indicated phase domains larger than a hundred nanometers.
• Demonstrated the coexistence of solid-ordered and liquid-disordered phases.
• Identified specific phonon propagation directions sensitive to different aspects of bilayer structure.

Conclusions:

• Brillouin spectroscopy is a viable tool for probing nanoscale heterogeneity in lipid bilayers.
• Lateral phonons are effective for assessing bilayer homogeneity.
• Normal phonons provide insights into mesoscopic layered packing within bilayers.