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In this work, we study the interaction of a well-known photosensitizer, MePha, with models of biological membrane (Langmuir monolayers and Langmuir-Schaeffer planar bilayers) based on one of the most important natural lipid, POPC, for the subsequent investigation of photodestruction processes in a context of photodynamic therapy treatment. Changes of macroscopic properties and morphology of POPC/MePha model membranes upon irradiation by visible light are recorded by means of contact angle measurements and atomic force microscopy, demonstrating clearly the possibility to use these methods for the study of photodestruction of artificial lipid membranes on solid substrates, but also for a comparative study of the efficiency of novel photosensitizers. [ABSTRACT FROM AUTHOR]

Under ambient conditions, a water film is always present on a silica substrate and generates additional capillary forces between the nanotip and the studied surface. In the present paper, we report AFM measurements of pull-off and friction forces as a function of the temperature and a comparative FTIR spectroscopy study. The AFM results show a net decrease of the forces as the temperature increases, while the IR spectroscopy indicates that the liquid film is removed at high temperature. Consequently, we deduce that a liquid neck is created between the tip and the surface and that the forces measured are mostly capillary forces. The present work shows that temperature studies with AFM can be a useful way to probe the influence of the capillary force in turn to characterize surface properties. [ABSTRACT FROM AUTHOR]