Formation and colloidal stability of DMPC supported lipid bilayers on SiO2 nanobeads.

Supported lipid bilayers (SLBs) of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) were formed on 20-100 nm silica (SiO(2)) nanobeads, and the formation was accompanied by an 8 nm increase in diameter of the SiO(2), consistent with single nanobeads surrounded by a DMPC bilayer. Complete SLBs were formed when the nominal surface areas of the DMPC matched that of the silica, SA(DMPC)/SA(SiO2) = 1, and required increasing ionic strength and time to form on smaller size nanobeads, as shown by a combination of nano-differential scanning calorimetry (nano-DSC), dynamic light scattering (DLS), and zeta potential (zeta) measurements. For 5 nm SiO(2), where the nanoparticle and DMPC dimensions were comparable, DMPC fused and formed SLBs on the nanobeads, but it did not form single bilayers around them. Instead, stable agglomerates of 150-1000 nm were formed over a wide surface ratio range (0.25 < or = SA(DMPC)/SA(SiO2) < 2) in 0.75 mM NaCl. At ionic strengths > 1 mM NaCl, charge shielding, as measured by zeta potential measurements (zeta --> 0), resulted in precipitation of the SLBs.