Influence of NaCl Concentration on Bicelle-Mediated SLB Formation

The deposition of two-dimensional bicellar disks on hydrophilic surfaces is an emerging approach to fabricate supported lipid bilayers (SLBs) that requires minimal sample preparation, works at low lipid concentrations, and yields high-quality SLBs. While basic operating steps in the fabrication protocol mimic aspects of the conventional vesicle fusion method, lipid bicelles and vesicles have distinct architectural properties, and understanding how experimental parameters affect the efficiency of bicelle-mediated SLB formation remains to be investigated. Herein, using the quartz crystal microbalance-dissipation and localized surface plasmon resonance techniques, we investigated the effect of bulk NaCl concentration on bicelle-mediated SLB formation on silicon dioxide surfaces. For comparison, similar experiments were conducted with vesicles as well. In both cases, SLB formation was observed to occur rapidly provided that the NaCl concentration was sufficiently high (>50 mM). Under such conditions, the effect of NaCl concentration on SLB formation was minor in the case of bicelles and significant in the case of vesicles where it is expected to be related primarily to osmotic pressure. At lower NaCl concentrations, bicelles also formed SLBs but slowly, whereas adsorbed vesicles remained intact. These findings were complemented by time-lapsed fluorescence microscopy imaging and fluorescence recovery after photobleaching measurements that corroborated bicelle-mediated SLB formation across the range of tested NaCl concentrations. The results are discussed by comparing the architectural properties of bicelles and vesicles along with theoretical analysis of the corresponding adsorption kinetics.