ChemMatCARS Nuggets - Materials Science

Monitoring X-Ray Beam Damage on Lipid Films
with an Integrated Brewster Angle Microscope/X-ray Diffractometer

Accomplishment
Beam damage to biologically relevant systems has long been problematic. In this study, we combined Brewster angle microscopy with grazing incidence X-ray diffraction (GID) in a new instrument, which we used to study phospholipid monolayers at the air-water interface. While beam damage has been observed in data measurements, it has not previously been viewed in situ during irradiation. In this study, we quantified the effects of radiative damage and linked them to optical changes in the film. For condensed lipid systems, a change in the thickness of the film was observed. This change corresponds to the loss of order seen by GID. In addition, by monitoring the motion of the film and using isotherm data, we were able to determine the amount of material lost from the surface during irradiation.

Side view of the integrated Brewster angle microscope/X-ray diffractometer

Impact
While x-ray beam damage has been observed experimentally for more than a century, it has not before been optically observed during irradiation. This instrument will allow researchers to link the optical changes in their films with x-ray exposure. For dynamic systems, researchers will be able to follow the progression of an experiment under irradiation and to determine the effect of radiation, if any, on the system being studied. With this information, they can modify the experiment to limit the effect of radiative exposure.

A monolayer of dimyristoylphosphatidylserine at 25 mN/m before (left) and after (right) irradition. During irradiation the film shows areas of decreased thickness. In the x-ray data, a steady decrease in the order of the system is seen as a function of irradiation.

September 2007

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