Adsorption of Cationic Lipid Bilayer onto Flat Silicon Wafers:  Effect of Ion Nature and Concentration

Abstract

The effect of monovalent salt nature and concentration over a range of low ionic strengths (0-10 mM LiCl, NaCl, KCl, or CsCl) and at two different pH values (6.3 and 10.0) on adsorption of dioctadecyldimethylammonium bromide (DODAB) bilayer fragments (BF) onto flat SiO(2) surfaces was systematically evaluated by means of in situ ellipsometry. High-affinity adsorption isotherms fitted by the Langmuir model indicated that adsorption maxima were consistent with bilayer deposition only around 10 mM monovalent salt at both pH values. In pure water, the mean thickness of the DODAB adsorbed layer was close to zero with bilayer deposition taking place only around 10 mM ionic strength. In the presence of 10 mM CsCl or LiCl, the highest and the lowest affinity constants for DODAB adsorption onto SiO(2) were, respectively, obtained consistently with the expected facility of cation exchange at the surface required for DODAB adsorption. The cation more tightly bound to the solid surface should be Li(+), which would present the largest resistance to displacement by the DODAB cation, whereas the less tightly bound cation should be Cs(+) due to its largest ionic radius and lowest charge density. In other words, DODAB adsorption proceeds in accordance with charge density on the solid surface, which depends on the nature and concentration of bound counterions as well as DODAB cation ability to displace them. AFM images show a very smooth DODAB film adsorbed onto the surface in situ with a large frequency of BF auto-association from their edges. The present results for flat surfaces entirely agree with previous data from our group for DODAB adsorption onto silica particles.

Assembly of horseradish peroxidase within supported cationic bilayers

“…A complete study on effects of monovalent salt nature and concentration over a range of low ionic strengths (0-10 mM LiCl, NaCl, KCl, or CsCl) and at two different pH values (6.3 and 10.0) on adsorption of DODAB BF onto flat SiO 2 surfaces had to be done to optimize bilayer deposition from in situ ellipsometry. 21 In pure water, the mean thickness of the DODAB adsorbed layer was close to zero with bilayer deposition taking place only around 10 mM ionic strength. In the presence of 10 mM CsCl or LiCl, the highest and the lowest affinity constants for DODAB adsorption onto SiO 2 were, respectively, obtained consistently with the expected facility of cation exchange at the surface required for DODAB adsorption.…”

“…29 For silicon wafers, the interaction of DODAB BF and wafer to obtain optimal bilayer deposition was done in a 10 mM CsCl solution. 21 The reason for employing CsCl is not obvious. A complete study on effects of monovalent salt nature and concentration over a range of low ionic strengths (0-10 mM LiCl, NaCl, KCl, or CsCl) and at two different pH values (6.3 and 10.0) on adsorption of DODAB BF onto flat SiO 2 surfaces had to be done to optimize bilayer deposition from in situ ellipsometry.…”

“…Coating with cationic lipids has been applied to silica, 17 latex, 18 or hydrophobic drug particles. 19 Optimal cationic bilayer deposition on polymeric particles 20 or silicon wafers 21 has been demonstrated to take place with certain compositions of the intervening medium, as determined from experiments involving systematic variation of counter-ion type and concentration and the proportion of surface areas for bilayers and particles or surfaces. Recently, this optimal cationic bilayer coverage on polystyrene sulfate (PSS) nanoparticles allowed successful presentation of protein antigens to the immune system.…”

“…The cationic bilayer was supported as previously described on two different substrates: (1) PSS particles 18,20 ; (2) silicon wafers. 21 Thereafter, incorporation was determined from HRP depletion in supernatants of centrifuged PSS/DODAB and HRP mixtures. Size distribution, zeta-potential, and polydispersity index were determined from dynamic light scattering for all dispersions.…”

Lipid-based Biomimetics in Drug and Vaccine Delivery

“…Silica Carmona-Ribeiro,1997, 2000;Moura and CarmonaRibeiro, 2005, 2006, 2007, latex (Carmona-Ribeiro and Midmore, 1992; or hydrophobic drug particles (Pacheco and Carmona-Ribeiro, 2003;) have been coated with cationic lipids. Optimal cationic bilayer deposition on particles was achieved by coalescence of bilayer fragments at www.intechopen.com adequate experimental conditions for the intervening medium such as pH, ionic strength and concentrations of the interacting components (Moura & Carmona-Ribeiro, 2003;Moura & Carmona-Ribeiro, 2005;Pereira et al, 2004;Pereira et al, 2006). Recently, the optimal bilayer coverage of polystyrene sulfate (PSS) nanoparticles with a cationic dioctadecyldimethylammonium bromide (DODAB) bilayer found an important application adsorbing and successfully presenting antigens to the immune system Lincopan et al, 2009a).…”