(192q) Investigating Phase Fractions of DPPC-Hexadecanol Monolayers Using Fluorescence Microscopy of Langmuir Films

Surfactant is an essential part of the respiratory system, allowing the lungs to expand and contract while remaining hydrated. Gaining an understanding of its mechanisms is necessary for the treatment of many respiratory-related illnesses. Under certain compositions, three lung surfactant components - dipalmitoylphosphatidicholine (DPPC), hexadecanol, and cholesterol - can be observed to pack in unique crystal structures. The samples are spread on an aqueous interface to create a molecule-thick "monolayer," which may be compressed or expanded to change the surface pressure. As the surface pressure increases, the components co-crystalize, changing the relative liquid and solid phase fractions of the monolayer. Through the use of confocal microscopy and Langmuir monolayer compression, samples at various surface pressures can be imaged. The solid and liquid phase fractions may be measured using a variety of fluorescent probes. It is found that the choice of fluorescent probe may influence the observed monolayer morphology. In addition, the surface viscosity of the monolayer can be measured and related using an analytical expression via scaling arguments to the area fraction measurements. From this, we can gain a better understanding of the function of lung surfactant components to better treat respiratory conditions.