Effect of the Surface Hydrophilicity on the Formation of a Membrane-type Interface: Study Using an Acoustic Wave Device

Abstract

An acoustic wave device was used to study the deposition of lipid vesicles on solid surfaces of different hydrophilicity. The device operated at 103 MHz and consisted of a quartz substrate with a polymer overlayer acting as an acoustic waveguide and a thin layer of gold. The hydrophilicity of the device surface was controlled by modifying the gold surface with hexadecanethiol (HDT) for 16 h and mercaptoundecanol (MUO) for 10 min and 16 h in order to obtain a hydrophobic, relatively hydrophilic, and hydrophilic surface, respectively. The interaction of a vesicle suspension of 2-oleoylpalmitoyl-sn-glycero-3-phosphocholine (POPC) in PBS with each surface was monitored by recording the phase and amplitude of the acoustic wave in real time. The acoustic signal detected on the hydrophobic (HDT) and hydrophilic (16 h MUO) surfaces indicated the formation of a supported monolayer and bilayer, respectively, while a vesicle layer was detected on the less hydrophilic (10 min MUO) surface. The above findings were confirmed by using 14C-labeled lipids and by monitoring the nonspecific binding of BSA on each surface. These experiments clearly showed that the hydrophilic properties of the solid surface are very important for designing a two dimensionsional (bilayer) or three-dimensional (vesicle) membrane-type interface layer. Furthermore, the simultaneous monitoring of the phase and amplitude of the acoustic wave was shown to provide complementary information related to mass and viscoelastic interfacial changes.