3D Probed Lipid Dynamics in Small Unilamellar Vesicles

Area of Science:

• Biophysics
• Membrane Biophysics
• Single-Molecule Biophysics

Background:

• Optical microscopy has resolution limits (10-20 nm), hindering nanoscale investigations.
• Lipid dynamics in small unilamellar vesicles (SUVs) are crucial for membrane function.
• Single-molecule techniques offer higher resolution for studying membrane properties.

Purpose of the Study:

• To investigate lipid dynamics and organization within small unilamellar vesicles (SUVs).
• To explore the influence of cholesterol on membrane properties and oxygen transport.
• To visualize membrane heterogeneity at the nanoscale using advanced spectroscopic methods.

Main Methods:

• Utilized single-molecule fluorescence correlation spectroscopy (SMFCS).
• Acquired fluorescence trajectories of lipid-like tracer 1,1'-dioctadecyl-3,3,3',3'-tetramethylindodicarbocyanine (DiD) at the single-molecule level.
• Performed autocorrelation analysis and 2D spectral analysis correlating diffusion coefficient and triplet-state lifetime.

Main Results:

• Cholesterol addition restricts isomerization and affects lipid organization within SUVs.
• Oxygen transport is hindered in ultrasmall clusters and cholesterol-rich regions but occurs in liquid-disordered phases and defects.
• 2D spectra precisely visualized membrane heterogeneity, including lipid domains, packing defects, and DiD-induced clusters.

Conclusions:

• SMFCS provides kinetic information on lipid organization, oxygen transport, and diffusion in SUV membranes.
• Cholesterol plays a significant role in modulating membrane dynamics and permeability.
• The study successfully visualized nanoscale membrane heterogeneity, offering insights into lipid packing and domain formation.