Time-Resolved Fluorescence Anisotropy of a Molecular Rotor Resolves Microscopic Viscosity Parameters in Complex...

Area of Science:

• Biophysics
• Chemical Physics
• Cell Biology

Background:

• Understanding viscosity in complex biological environments is crucial for determining in vivo reaction rates.
• Heterogeneous environments present challenges for accurate viscosity measurements.

Purpose of the Study:

• To develop a method for simultaneously determining two non-equivalent viscosity-related parameters in complex heterogeneous environments.
• To investigate the behavior of fluorescent molecular rotors (FMRs) in lipid-based nano-environments.

Main Methods:

• Utilized time-resolved fluorescence anisotropy imaging (TR-FAIM) combined with fluorescent molecular rotors (FMRs).
• Analyzed fluorescence anisotropy decays exhibiting dip-and-rise behavior characteristic of heterogeneous environments.
• Employed molecular dynamics simulations to assign FMR populations to specific nano-environments.

Main Results:

• Successfully extracted FMR rotational correlation time and lifetime from complex anisotropy decays.
• Observed distinct FMR populations in both artificial adiposomes and live cell lipid droplets.
• Correlated less viscous environments with a 25° lipid membrane tilt and more viscous environments with a 55° tilt.

Conclusions:

• The combined TR-FAIM and FMR approach provides a comprehensive description of probe behavior in viscous nano-environments.
• This method offers new insights into the viscosity of complex biological systems.
• The study elucidates the relationship between molecular orientation and local viscosity in lipid systems.