Surface structure, membrane proteins probe technique

The properties of membranes commonly studied by fluorescence techniques include motional, structural, and organizational aspects. Motional aspects include the rate of motion of fatty acyl chains, the head-group region of the phospholipids, and other lipid components and membrane proteins. The structural aspects of membranes would cover the orientational aspects of the lipid components. Organizational aspects include the distribution of lipids both laterally, in the plane of the membrane (e.g., phase separations), and across the membrane bilayer (phospholipid asymmetry) and distances from the surface or depth in the bilayer. Finally, there are properties of membranes pertaining to the surface such as the surface charge and dielectric properties. Fluorescence techniques have been widely used in the studies of membranes mainly since the time scale of the fluorescence lifetime coincides with the time scale of interest for lipid motion and since there are a wide number of fluorescence probes available which can be used to yield very specific information on membrane properties. 

Atomic force microscopy (AFM) is an experimental technique that uses an extremely sharp probe to measure the nanoscale structure of surfaces. Membranes can have an interesting structure on this length scale if there are lipid domains or transmembrane proteins present, for example, the lipid rafts discussed in Section 6.3.2 and associated proteins. AFM can be used to map the topology of a model lipid bilayer or extracted biological membrane if the membrane can be transferred to a very smooth surface. 

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