First observation of 3D aggregates in a single-component Langmuir film below the equilibrium spreading pressure

Abstract

Abstract. Single component monolayers from Dipalamitoyl Phosphatidyl Ethanolamine head labelled with the fluorescent chromophore NitroBenzoxaDiazole (DP-NBD-PE) were investigated at the air-water interface as Langmuir films and deposited on silicon wafers or glass plates as Langmuir-Blodgett (LB) films. A step compression and monitoring of the pressure relaxation together with domain formation as observed with Brewster angle microscopy suggests that main transition from liquid expanded to liquid compressed state start at around 6.9 mN/m though on the isotherm it starts around 9 mN/m at 25 o C. Brewster angle microscopy also reveals a nonuniform structure in the monolayer. 3D aggregates -cylinders with 50 -150 nm diameter and bilayer height were observed with Atomic Force Microscopy when deposition was carried at 7 mN/m, above the main phase transition but considerably lower than the equilibrium spreading pressure of 19.6 mN/m for this molecule. When LB film deposition is carried just below the main phase transition a uniform height layer of film in a liquid phase is observed with AFM with no structures. Both compression and deposition were carried at very low speeds with large time to relax in ordered to avoid kinetic effects. These 3D aggregates are not due to the transfer process or interaction with the substrate. These aggregates provide a highly developed area combined with monolayer thick structure which can produce very fast and highly sensitive biosensors.

Reversible Monolayer–Bilayer Transition in Supported Phospholipid LB Films under the Presence of Water: Morphological and Nanomechanical Behavior

“…The monolayer to bilayer transition is schematized in Figure (bottom cartoon). Such a reorganization mechanism, in which the alkyl chains interactions between neighbor molecules are maximized, is well-known to occur for instance in self-assembled monolayers of thiol derivatives, and also in biomaterials that tend to form mono and bilayer fibrous aggregates. , A similar effect, that is, formation of a phospholipid monolayer from a supported lipid bilayer, has already been reported for different combinations of lipids and substrates. − In general, this phenomenon has been mainly attributed to the known instability exhibited by supported phospholipid bilayers exposed at the air interface, since air is expected to be more hydrophobic than aqueous solutions. This instability originates when the air reaches the bilayer giving rise to a disorganization of the bilayer structure .…”

Layer by Layer Optimization of Langmuir–Blodgett Films for Surface Acoustic Wave (SAW) Based Sensors for Volatile Organic Compounds (VOC) Detection

“…The water resistance was measured as 18.2 MΩ and no noticeable surface-active contamination was observed. After spreading of the LB solution on the air-water interface, at least 25 min was allowed for the solvent to evaporate, as shown by Brewster angle microscopy [17].…”

“…We called these solutions the hexane dissolved arachidic acid (HDAA) and chloroform dissolved arachidic acid (CDAA). We also tested single monolayers of a fluorescently labeled phospholipid (SLP) DPPE-NBD that forms 3D aggregates [17] and thus a surface with a high surface-to-volume ratio, high sensitivity, and fast response time is created [18]. We present the optimization and performance of a VOC detection sensor using a SAW-based two-port resonator as a highly sensitive QSM whose active sensing area had been functionalized with the above CDAA, HDAA, or SLP materials using the LB deposition method.…”

Langmuir-Blodgett Films of Arachidic and Stearic Acids as Sensitive Coatings for Chloroform HF SAW Sensors

“…Further, the price of around 500 EUR /1 mg of the DPPE-NBD molecule with high purity is prohibitive for mass production. The high sensitivity of the DPPE-NBD LB film monolayers can be explained by the well-developed 3D structure with a very high surface-to-volume ratio [ 25 , 26 ]. In a previous study, when the gas sensitivity of self-assembled molecules with different chemistry of the tails was compared among nine different types, the hydrocarbon CH 2 group tales exhibited the second highest gas absorption properties [ 27 ].…”