Atomic force microscopy (AFM) is a powerful tool for direct
visualization of supported biological membranes [1]. Moreover, in-situ
AFM measurements permit investigations of biological phenomena in real
time and in physiological environments. In a previous work, we have
studied the morphology and stability of supported phospholipid layers
prepared by solution spreading (casting) on mica [2]. The images were
acquired in the contact or contact-intermittent modes and the samples
analyzed ex-situ just after solvent evaporation and after a hydration
step, and in-situ with immersion in a buffer solution. Contact-mode
imaging is less suitable for soft or weakly attached materials, since
the tip can often scrape or drag the membranes during scanning, a
disadvantage that can be overcome by applying intermittent methods.
However, studies have also demonstrated that by adjusting the operative
force it is possible to use contact-mode to obtain AFM images of soft
phospholipids layers [3]. In the present work, we applied successfully
in-situ AFM contact-mode to characterize phospholipid layers of
1,2-dimyristoyl-sn-glycero-3-phosphatitidylcholine (DMPC) and
1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC), as well as a
binary mixture of these phospholipids. The supported membranes were
prepared on mica substrates by vesicle fusion method.
Dye rejection membranes prepared from oxidized graphite particles