Investigation of Langmuir-Blodgett films from fluorescently labelled phospholipids with fluorescence lifetime spectroscopy and atomic force microscopy

Abstract

Fluorescently head labelled phospholipids form stable organized organic monolayers at the air-water interface (Langmuir films) and can be deposited on solid supports (glass or Surface Plasmon Resonance (SPR)) substrates as Langmuir-Blodgett (LB) films. In a subsequent work LB mono- and multilayers were deposited on Surface Acoustic Wave (SAW) devices. LB monolayers are very stable and hard to remove while the multilayers, typically for phospholipids, are difficult to deposit and can be removed more easily. Several new effects were discovered in Dipalmitoyl Phosphatidyl Ethanolamine head labelled with NitroBenzoxaDiazole (DPPE-NBD) molecule in the past which still need detailed explanation. Previous research of the Langmuir film was combined with the present study of fluorescence spectra and decay kinetics of LB monolayers and a 15 layer SPR substrate, which is a plastic substrate with gold evaporated electrodes. Langmuir-Blodgett films were deposited as monolayers or multilayers on glass or gold structured supports at different surface pressures and from either pure water subphase or with presence of Cadmium ions (Cd2+) in the water subphase. Atomic force microscopy reveals phase coexistence of liquid phase, solid phase and bilayer or higher height hundreds of nanometers in diameter cylinders. This rich polymorphism leads to complicated fluorescence lifetime spectra. Understanding of the structure and aggregation in these films can help with their possible future applications.