Chemical Imaging of Lipid Segregation: Determining Different Length Scales of Heterogeneity with Compressive-Sensing Sum Frequency Generation Microscopy and Brewster Angle Microscopy

• DOI: 10.1021/acs.jpcb.2c03493
• Publication Date: 2022-07-23T19:51:30Z
• Authors: Fangyuan Yang; Steven Baldelli
• Keywords: Brewster's angle

Membranes of various phospholipids may separate into different domains at micrometer length scales the air-water interface. A significant challenge is to visualize molecular organization and obtain chemical information on this surface. Langmuir-Blodgett monolayers 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) fused silica were investigated with compressive sensing sum frequency generation (SFG) microscopy. Before after mixing, SFG spectra for DSPC DLPC revealed differences, indicating a structural change. Brewster angle microscopy images show phase separations that directly correlate morphology phospholipid mixtures images. Exploiting vibrational contrast in images, exchange between two phases was discovered, quantitative thermodynamic analysis lipid compositions liquid-condensed liquid-expanded (LE) provided. Local reveal differences from one another, heterogeneity resulting domain areas distinct orientation conformation. Further across boundary presented finer scale, revealing an effect due condensed DSPC, terminal methyl perturbs ordering LE phase. This work demonstrates two-dimensional binary system mainly aliphatic chain transition temperature difference.