Light scattering microscopy (LSM) is introduced here as a versatile techniq
ue for the study of interfacial films at the air/water interface. Laser lig
ht scattered from the interface is collected by a microscope objective and
imaged onto a CCD camera. LSM allows determination of the spatial distribut
ion of submicron particles, phase transitions in two-dimensions, and defect
s. The power of LSM, especially if conducted simultaneously with fluorescen
ce microscopy or Brewster angle microscopy (BAM), is illustrated in three e
xamples. (a) Visualization of the spatial distribution of nanoscale particl
es with respect to monolayer phases: calcium oxalate crystals were grown un
derneath dipalmitoyl phosphatidyl choline (DPPC) and dimyristoyl phosphatid
yl serine (DMPS) monolayers in the liquid expanded/liquid condensed (LE/LC)
phase coexistence. The density of light scatterers was considerably higher
in the respective LE than the LC phase, and a gradual migration of particl
es was observed towards the domain boundaries. A similar behavior was obser
ved for nanocrystals injected underneath lipid monolayers. (b) Probing two-
dimensional (2D) protein crystallization processes underneath functionalize
d lipid monolayers and the spatial distribution of crystal defects: strepta
vidin was crystallized as a model protein in 2D through coordination of exp
osed histidines on the protein surface to the monolayer-anchored metal chel
ator, Cu-DO-IDA. Vacancies were formed within the 2D protein crystals after
injection of the soluble metal chelator EDTA, and the spatial distribution
of vacancies was probed by LSM. (c) Detection of monolayer topographic tra
nsitions, corrugation and nanoscale budding: The phases of DPPC monolayers
were studied under isothermal compression. New nanoscale topographic transi
tions are observed by LSM if DPPC is compressed into the liquid condensed (
LC) state far below the collapse pressure. (C) 2000 Elsevier Science B.V. A
ll rights reserved.