Supported bilayers on silica

Adsorption isotherms for bilayer-forming synthetic amphiphiles or phospholi pids adsorbed from vesicles onto hydrophilic silica particles (Aerosil 0X-5 0) are obtained over a range of experimental conditions. Phosphatidylcholin e (PC), dipalmitoylphosphatidylcholine (DPPC), and dioctadecyldimethylammon ium bromide (DODAB) dispersed in 10 mM of two different buffers (Tris or He pes) at three different pH values as small unilamellar vesicles present aff inities for silica following the sequence DODAB > DPPC > PC. Deposition of phospholipid bilayers was favored by the presence of Tris as buffer, pH les s than or equal to 7.4, and temperatures above the phase transition tempera ture for the phospholipid bilayer. Interaction between DPPC vesicles and si lica at 65 degrees C for 1 h efficiently leads to bilayer deposition at max imal adsorption, if Tris is the buffer used. Consistently, wettability of S iO2 planar surfaces precisely under conditions of bilayer deposition (as de picted from the isotherms) in the presence of the lipid vesicles yielded a large increase on surface hydrophobicity for DPPC at 65 degrees C and DODAB at room temperature. Reduction of merocyanine 540 absorbance at 565 mm was used as a marker for bilayer deposition onto the silica particles. Upon in teraction 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 inciden t light. For DPPC at 65 degrees C and DODAB at room temperature, but not fo r PC, occurrence of bilayer deposition depicted from the adsorption isother ms is confirmed from the three techniques employed for detection, (C) 2000 Academic Press.