Growth analysis of PEI/DPPG self-assembled films by quartz crystal microbalance

Aiming to create heterostructures with intact liposomes, layer-by-layer (LbL) films of dipalmitoyl phosphatidyl glycerol (DPPG) liposomes alternated with the polyelectrolyte poly(ethyleneimine) (PEI) were characterized in situ using quartz crystal microbalance (QCM). The QCM data analysis allows to infer that DPPG adsorbed amount is dependent of the number of bilayers already adsorbed, increasing from 24 mg/m2 for the first bilayer to a constant value of 103±14 mg/m2 after the 4th bilayer. This dependence was interpreted by the evolution of the roughness with the number of bilayers which increases until a maximum and after that decreases to a constant value. Kinetic curves reveals that the DPPG adsorption is justified by two processes, one which is associated to a adsorption of DPPG liposomes with a small constant time independent of the number of bilayers and another, dependent of the number of bilayers, associated to a structural rearrangement of DPPG liposomes on the surface.