Bi- and tetra-layered dipalmitoyl phosphatidylserine (DPPS) patterns produced by hydration of Langmuir-Blodgett monolayers and the subsequent enzymatic digestion

The preparation and characterization of patterns on atomically flat substrates (Si and Au(111)) composed of compact, bi- or tetra-layered dipalmitoyl phosphatidylserine (1,2-dipalmitoyl-sn-glycero-3-[phospho-L-serine] sodium salt, DPPS) regions and exposed substrate surfaces are described. Hydration of a monolayer or sub-monolayer of DPPS transferred onto a solid substrate using a Langmuir-Blodgett (LB) trough results in detachment of DPPS molecules weakly adhered to the substrate and their subsequent stacking onto DPPS molecules that are more strongly withheld by the substrate. The pattern and its thickness can be controlled by varying the surface pressure in which DPPS is transferred from the air/water interface in the LB trough and changing the surface properties of the substrates. Time-lapse atomic force microscopic imaging of phospholipase (PLA(2)) hydrolysis of the DPPS pattern and spectrofluorimetric measurements in the PLA(2) solution used to digest the dansyl-DPPS/DPPS pattern reveal that the topmost layer (terrace) on the pattern is compact and defects mainly exist at the edges of the pattern. Moreover, upon extensive PLA(2) digestion, a small amount of DPPS molecules remains at the substrate and the thickness of the residue corresponds to that of a bilayer. Quantification of the amount of DPPS molecules remaining at the surface via spectrofluorimetry indicated that very few lipid molecules, if any, were lost during the DPPS monolayer hydration and pattern formation. (c) 2008 Elsevier B.V. All rights reserved.