Near‐field scanning optical microscopy studies of l‐α‐dipalmitoylphosphatidylcholine monolayers at the air–liquid interface

Abstract

The phase structure in l‐α‐dipalmitoylphosphatidylcholine–2.0 mol% fluorescent 1,1′‐dioctadecyl‐3,3,3′,3′‐tetramethylindocarbocyanine perchlorate Langmuir monolayers dispersed on a 2 m sucrose solution subphase is studied with near‐field scanning optical microscopy (NSOM). Cantilevered NSOM probes operating in a tapping‐mode feedback or an optical interferometric feedback mode are capable of tracking the air–sucrose solution interface. At the micrometre scale, the NSOM fluorescence images reveal lipid domain features similar to those observed previously in supported Langmuir–Blodgett (LB) monolayers. At the submicrometre scale, the small nanometric lipid islands seen in LB films are not observed at the air–sucrose interface. This supports a mechanism in which domain formation in LB films can be induced by means of the transfer process onto the solid support. Progress towards extending these studies to films at the air–water interface using the optical interferometric feedback method is also discussed.

Near-Field Scanning Optical Microscopy: A New Tool for Exploring Structure and Function in Biology

“…A noncontact interferometric approach for controlling the NSOM tip-sample gap was shown to be gentle enough to image the air-liquid interface while in feedback [56]. This approached took advantage of the differences in path length for photons directly exiting the NSOM probe and those reflected off the sample surface as the probe approached the surface.…”