Nanopatterning and Functionalization of Phospholipid-Based Langmuir-Blodgett and Langmuir-Schaefer Films

In the past two decades, the Langmuir-Blodgett (LB) technique has emerged as a bottom-up route to create nanostructured ultrathin films. Patterns consisting of parallel stripes, ∼100 to 200 nm in width, were generated via the LB deposition of mixed monolayers of 1,2-dilauroyl- sn-glycero-3-phosphocholine (DLPC), and 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) onto silicon and mica substrates. To expand the functionality of these patterns, 1-palmitoyl-2-(16-( S-methyldithio)hexadecanoyl)-sn-glycero- 3-phosphocholine (DSDPPC) and 1-lauroyl-2-(12-(S-methyldithio)dodecanoyl)- sn-glycero- 3-phosphocholine (DSDLPC) were used to prepare chemically heterogeneous films. These phospholipid analogues have a methyldisulfide group attached to one of the alkyl chain ends. An extensive study of the phase structure of Langmuir, Langmuir-Shaefer and LB films of DSDPPC and DSDLPC and their mixtures with DPPC or DLPC is presented in this thesis.;The gel-to-liquid crystalline transition temperature of DSDPPC was determined to be 44.5 +/- 1.5 °C versus 41.5 +/- 0.3 °C for DPPC by DSC and turbidity measurements. The pressure-area isotherm of DSDPPC is similar to that of DPPC. The monolayer undergoes a liquid expanded-to-condensed (LE-C) phase transition at a surface pressure slightly higher than that of DPPC (6 mN m-1 vs. 4 mN m-1). Like DLPC, DSDLPC remains in the LE phase until the film collapse. The disulfide-modified lipids exist in a more expanded state throughout the monolayer compression and exhibit lower collapse pressures than the unmodified phospholipids.;The domain morphologies of DPPC and DSDPPC at the air/water interface were compared using Brewster Angle Microscopy. DPPC forms a homogeneous monolayer at a surface pressure (pi) > 10 mN m-1, while flower-like domains exist in the DSDPPC monolayers until pi ∼ 30 mN m-1. Solid-supported DSDPPC films were prepared and characterized using various surface analysis techniques. The parallel stripe pattern previously obtained with mixtures of DPPC/DLPC was reproduced using DSDPPC/DLPC or DPPC/DSDLPC mixtures resulting in chemically-differentiated patterns. The average stripe width varied from 150 to 500 nm, depending on the lipid composition and deposition pressure.;The disulfide group of the analogues was exploited to (i) form self-assembled monolayers of phospholipids on gold and (ii) demonstrate the selective metallization of the disulfide-terminated areas of the stripe patterns. X-ray photoelectron spectroscopy (XPS) confirmed that the monolayer-bound disulfides react with Au vapor to form a gold-thiolate species. Thermally evaporated Au, Ag and Cu exhibit preferential absorption onto the modified lipids only at submonolayer coverages.;Limited control over the regularity and feature size of the DPPC/DLPC stripe pattern was achieved by varying the lipid composition, deposition pressure, and substrate withdrawal speed. A higher percentage of condensed versus fluid lipid, slower deposition speed, and lower surface pressure create more continuous and wider stripes. The addition of a lineactant, cholesterol, to the DPPC/DLPC 1:1 (mol/mol) mixture allowed the formation of parallel stripes at higher surface pressure.;Keywords: DPPC, DLPC, 1-palmitoyl-2-(16-(S-methyldithio)hexadecanoyl)- sn-glycero-3-phosphocholine, 1-lauroyl-2-(12-(S-methyldithio)dodecanoyl)- sn-glycero-3-phosphocholine, phase separation, Langmir-Blodgett, Langmuir-Schaefer, surface patterning, gold-thiolates, selective metallization...