Nanomechanics of phospholipid LB film studied layer by layer with AFM

Background: Phospholipid, a main component of cell membrane, has been explored as a model system of the cell membrane and temporary scaffold materials in recent studies. The mechanical properties of phospholipid layers are essentially interesting since it is involved in several biological processes. Results: Here, the nanomechanical properties such as indentation force, adhesion force and DMT (Derjaguin-Mller-Toporov) modulus of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) Langmuir-Blodgett (LB) films were analyzed layer by layer with Atomic Force Microscope (AFM) under deionized water condition. Conclusions: The penetration distances in the indentation force curves are equal to the thicknesses of phospholipid films, and the yield forces of DSPC LB films in deionized water are smaller than that of similar lipid films in buffered solutions due to the influence of ions. Moreover, the DMT modulus of upper layer DSPC LB film is different from that of monolayer DSPC LB film due to the influence of their different substrates. Our results suggest that environment such as surrounding ions and substrate will strongly influence the measured nano-mechanical properties of the lipid bilayer, especially that of the down layer.