Supported Bilayers On Silica

Abstract

Adsorption isotherms for bilayer-forming synthetic amphiphiles or phospholipids adsorbed from vesicles onto hydrophilic silica particles (Aerosil 0X-50) are obtained over a range of experimental conditions. Phosphatidylcholine (PC), dipalmitoylphosphatidylcholine (DPPC), and dioctadecyldimethylammonium bromide (DODAB) dispersed in 10 mM of two different buffers (Tris or Hepes) at three different pH values as small unilamellar vesicles present affinities for silica following the sequence DODAB > DPPC > PC. Deposition of phospholipid bilayers was favored by the presence of Tris as buffer, pH ≤ 7.4, and temperatures above the phase transition temperature for the phospholipid bilayer. Interaction between DPPC vesicles and silica at 65°C for 1 h efficiently leads to bilayer deposition at maximal adsorption, if Tris is the buffer used. Consistently, wettability of SiO2 planar surfaces precisely under conditions of bilayer deposition (as depicted from the isotherms) in the presence of the lipid vesicles yielded a large increase on surface hydrophobicity for DPPC at 65°C and DODAB at room temperature. Reduction of merocyanine 540 absorbance at 565 nm was used as a marker for bilayer deposition onto the silica particles. Upon interaction with the solid particle, absorbance at 565 nm displays a decrease with time that corresponds to the percentage of dye sandwiched between the bilayer and the solid particle surface and thereby hidden from the incident light. For DPPC at 65°C and DODAB at room temperature, but not for PC, occurrence of bilayer deposition depicted from the adsorption isotherms is confirmed from the three techniques employed for detection.