Dilational rheology of an air–water interface functionalized by biomolecules: the role of surface diffusion

As an attempt to develop a sensitive device for biomolecule detection, a micromechanical methodology based on the rheological change of an air–water interface is put forward (Berthier and Davoust, CEA/CNRS patent, PCT International Application WO 2003/080209 A3, 2003). Capillary waves induced from the vertical electrodynamic vibration of a brimful cylindrical tank filled with water stand as a good way to identify dilational elasticity and viscosity of an aging interface. Before, we were interested of the fact that complex wave number and the frequency of waves are obtained through an optical technique, which allows us to accurately recognize the whole interface geometry. These two parameters, a modeling based on a dispersion relation (Lucassen-Reynders and Lucassen, Adv Colloid Interface Sci, 2:347, 1969) and the surface mass transport equation, are jointly used to identify the surface diffusivity and the dilational rheology of the interface for a nonsoluble biochemical surfactant. Preliminary results obtained from a water surface functionalized by DNA, thanks to a lipidic monolayer, demonstrate the capabilities of the proposed methodology. The sensitivity of dilational rheology and the surface diffusivity on DNA adsorption on lipids is made evident.