Tapping-mode atomic force microscopy on intact cells: optimal adjustment of tapping conditions by using the deflection signal

Difficulties in the proper adjustment of the scanning parameters are often encountered when using tapping-mode atomic force microscopy (TMAFM) for ima ging thick and soft material, and particularly living cells, in aqueous buf fer. A simple procedure that drastically enhances the successfull imaging o f the surface of intact cells by TMAFM is described. It is based on the obs ervation, in liquid, of a deflection signal, concomitant with the damping o f the amplitude that can be followed by amplitude-distance curves. For inta ct cells, the evolution of the deflection signal, steeper than the amplitud e damping allows a precise adjustment of the feedback value. Besides its us e in finding the appropriate tapping conditions, the deflection signal prov ides images of living cells that essentially reveal the organization of the membrane cytoskeleton. This allows to show that changes in the membrane su rface topography are associated with a reorganization of the membrane skele ton. Studies on the relationships between the cell surface topography and m embrane skeleton organization in living cells open a new field of applicati ons for the atomic force microscope. (C) 2000 Elsevier Science B.V. All rig hts reserved.