Molecular composition and orientation in myelin figures characterized by coherent anti-stokes Raman scattering microscopy.

The molecular organization inside myelin figures of various surfactants are studied by laser scanning coherent anti-Stokes Raman scattering (CARS) microscopy that permits three-dimension vibrational imaging. The resonant CARS signals from CH 2 and H 2 O stretch vibrations are used to probe the surfactant and water molecules inside the myelin figures formed of C 12 E 3 , lecithin, and Aerosol OT. The polarization sensitivity of CARS is used to analyze the orientation of the CH 2 groups and the H 2 O molecules. The CARS images suggest that the myelin figure is a concentric lamellar structure with alternating surfactant bilayers and partially ordered water layers. No sizable water core is observed in the CARS images at the lateral resolution of 0.3 μm and the axial resolution of 0.75 μm. The CARS data are verified by confocal fluorescence microscopy with FITC and DOPE-rhodamine labeling the water and bilayers, respectively. The relationship between the molecular composition and ordering inside the myelin figures and the surfactant structure has been investigated.