Multiphoton excitation fluorescence microscopy in planar membrane systems

Area of Science:

• Biophysics
• Materials Science
• Surface Chemistry

Background:

• Lipid monolayers at the air-water interface (Langmuir films) are crucial model systems for biological membranes.
• Characterizing lipid packing and domain coexistence in these films is challenging with conventional methods.

Purpose of the Study:

• To assess the applicability of multiphoton excitation fluorescence microscopy for studying Langmuir films.
• To utilize the environmental-sensitive probe LAURDAN for detailed membrane analysis.

Main Methods:

• Non-linear fluorescence microscopy utilizing the LAURDAN probe.
• Measurement of the LAURDAN generalized polarization (GP) function.
• Comparison of Langmuir film data with planar bilayer systems.

Main Results:

• LAURDAN provides homogeneous distribution and simultaneous information from coexisting domains in Langmuir films.
• Photoselection effects of LAURDAN allow inference of monolayer tilting and visualization of 3D structures at film collapse.
• LAURDAN GP values in monolayers correspond to molecular areas in bilayers at specific lateral pressures for DOPC and DPPC.

Conclusions:

• Multiphoton microscopy with LAURDAN is a powerful technique for characterizing lipid packing and structure in Langmuir films.
• LAURDAN's sensitivity to lipid packing and its distribution properties overcome limitations of classical probes.
• The study establishes a quantitative link between lipid behavior in monolayers and bilayers.