Langmuir-Blodgett Monolayers Research Articles

The interfacial characteristic of mixed Cytochrome C/Cardiolipin Langmuir-Blodgett monolayer

心磷脂(CL)是真核细胞线粒体内膜中的主要磷脂之一. 细胞色素C (Cyt c)是线粒体内膜呼吸链的必要成分, 与许多疾病有关. 本文采用Langmuir-Blodgett技术结合原子力显微镜(AFM)研究了不同量的Cyt c与CL单层膜相互作用的特性. 结果表明, Cyt c在CL单层膜上吸附量存在阈值. 单层膜在5、10 mN/m膜压时经历压缩扩张循环后, 界面分子几乎无损失, 但是在20 mN/m膜压时, 界面分子出现损失. 通过Volmer理论模型定量计算界面分子损失的数量, 发现当Cyt c分别为0、2.5、5 μL时, 界面损失的分子占总分子数的1/1000, 当Cyt c分别为10、15 μL时, 界面损失的分子数占总分子数的1/100. 线粒体内膜中Cyt c的缺失或释放会引起某些疾病. 因此, 探究不同量Cyt c和CL之间的相互作用机理可为线粒体异常引起的疾病提供重要的信息.

Synthesis of Triptycene-Based Molecular Rotors for Langmuir-Blodgett Monolayers.

We describe syntheses of six triptycene-containing molecular rotors with several single-crystal X-ray diffraction analyses. These rod-shaped molecules carrying an axial rotator are designed to interleave on an aqueous surface into Langmuir-Blodgett (LB) monolayers containing a two-dimensional trigonal array of dipoles rotatable about an axis normal to the surface. Monolayer formation was verified with the simplest of the rotor structures. On an aqueous subphase containing divalent cations (Mg(2+), Ca(2+), Zn(2+), Sr(2+), or Cd(2+)), the LB isotherm yielded an area of 53 ± 3 Å(2)/molecule (monolayer of type A), compatible with the anticipated triangular packing of axes normal to the surface. On pure water, the area is 30 ± 3 Å(2)/molecule, and it is proposed that in this monolayer (type B), the molecular axes are tilted by 40-45° to a structure similar to those observed in single crystals of related triptycenes. After transfer to a gold surface, ellipsometry and PM IRRAS yield tilt angles of 29 ± 4° (monolayers of type A) and 38 ± 4° (type B). A full-scale examination of monolayers from all the rotors on a subphase and after transfer is underway and will be reported separately.

Cholesterol strongly affects the organization of lipid monolayers studied as models of the milk fat globule membrane: Condensing effect and change in the lipid domain morphology

The biological membrane that surrounds the milk fat globules exhibits phase separation of polar lipids that is poorly known. The objective of this study was to investigate the role played by cholesterol in the organization of monolayers prepared as models of the milk fat globule membrane (MFGM). Differential scanning calorimetry and X-ray diffraction experiments allowed characterization of the gel to liquid crystalline phase transition temperature of lipids, Tm ~35°C, in vesicles prepared with a MFGM lipid extract. For temperature below Tm, atomic force microscopy revealed phase separation of lipids at 30mN·m−1 in Langmuir–Blodgett monolayers of the MFGM lipid extract. The high Tm lipids form liquid condensed (LC) domains that protrude by about 1.5nm from the continuous liquid expanded (LE) phase. Cholesterol was added to the MFGM extract up to 30% of polar lipids (cholesterol/milk sphingomyelin (MSM) molar ratio of 50/50). Compression isotherms evidenced the condensing effect of the cholesterol onto the MFGM lipid monolayers. Topography of the monolayers showed a decrease in the area of the LC domains and in the height difference H between the LC domains and the continuous LE phase, as the cholesterol content increased in the MFGM lipid monolayers. These results were interpreted in terms of nucleation effects of cholesterol and decrease of the line tension between LC domains and LE phase in the MFGM lipid monolayers. This study revealed the major structural role of cholesterol in the MFGM that could be involved in biological functions of this interface (e.g. mechanisms of milk fat globule digestion).

The behavior of the adsorption of cytochrome C on lipid monolayers: A study by the Langmuir–Blodgett technique and theoretical analysis

Cytochrome c (Cyt c) is an essential component of the inner mitochondrial respiratory chain because of its function of transferring electrons. The feature is closely related to the interaction between Cyt c and membrane lipids. We used Langmuir–Blodgett monolayer technique combined with AFM to study the interaction of Cyt c with lipid monolayers at air–buffer interface. In our work, by comparing the mixed Cyt c-anionic (DPPS) and Cyt c-zwitterionic (DPPC/DPPE) monolayers, the adsorption capacity of Cyt c on lipid monolayers is DPPS>DPPE>DPPC, which is attributed to their different headgroup structures. π–A isothermal data show that Cyt c (v=2.5μL) molecules are at maximum adsorption quantity on lipid monolayer. Moreover, Cyt c molecules would form aggregations and drag some lipids with them into subphase if the protein exceeds the maximum adsorption quantity. π–T curve indicates that it takes more time for Cyt c molecular conformation to rearrange on DPPE monolayer than on DPPC. The compressibility study reveals that the adsorption or intermolecular aggregation of Cyt c molecules on lipid monolayer will change the membrane fluidization. In order to quantitatively estimate Cyt c molecular adsorption properties on lipid monolayers, we fit the experimental isotherm with a simple surface state equation. A theoretical model is also introduced to analyze the liquid expanded (LE) to liquid condensed (LC) phase transition of DPPC monolayer. The results of theoretical analysis are in good agreement with the experiment.

Monolayer-Mediated Growth of Organic Semiconductor Films with Improved Device Performance.

Increased interest in wearable and smart electronics is driving numerous research works on organic electronics. The control of film growth and patterning is of great importance when targeting high-performance organic semiconductor devices. In this Feature Article, we summarize our recent work focusing on the growth, crystallization, and device operation of organic semiconductors intermediated by ultrathin organic films (in most cases, only a monolayer). The site-selective growth, modified crystallization and morphology, and improved device performance of organic semiconductor films are demonstrated with the help of the inducing layers, including patterned and uniform Langmuir-Blodgett monolayers, crystalline ultrathin organic films, and self-assembled polymer brush films. The introduction of the inducing layers could dramatically change the diffusion of the organic semiconductors on the surface and the interactions between the active layer with the inducing layer, leading to improved aggregation/crystallization behavior and device performance.

The Relationship between Structural and Electrical Characteristics in Perylenecarboxydiimide‐Based Nanoarchitectures

The controlled assembly of the prototypical n‐type organic semiconductor N,N′‐1H,1H‐perfluorobutyl dicyanoperylenecarboxydiimide (PDIF‐CN2) into ordered nanoarchitectures and the multiscale analysis of the correlation between their structural and their electrical properties is reported. By making use of the Langmuir–Blodgett (LB) technique, monolayers of PDIF‐CN2 arranged in upright standing molecular packing on different substrates are formed. Postdeposition thermal treatment makes it possible to trigger a reorganization into layered ultrathin crystalline nanostructures, exhibiting structural and photophysical properties similar to those of microscopic crystals obtained by solvent‐induced precipitation. The controlled engineering of these molecular architectures on surfaces enables us to identify both a dependence of the monolayer resistance on the molecular tilt angle in vertical junctions and a pronounced charge‐transport anisotropy with enhanced transport along the π–π stacking direction of the PDI core. While a charge carrier mobility for electrons as high as 10–2 cm2 V–1 s–1 is determined in monolayer field‐effect transistors for the in‐plane direction, being the highest yet reported value for a n‐type LB monolayer, the out‐of‐plane mobility measured by conductive atomic force microscopy in multilayered structures is found to be one order of magnitude lower.

Direct observation of nanometer-scale pores of melittin in supported lipid monolayers.

Melittin is the most studied membrane-active peptide and archetype within a large and diverse group of pore formers. However, the molecular characteristics of melittin pores remain largely unknown. Herein, we show by atomic force microscopy (AFM) that lipid monolayers in the presence of melittin are decorated with numerous regularly shaped circular pores that can be distinguished from nonspecific monolayer defects. The specificity of these pores is reinforced through a statistical evaluation of depressions found in Langmuir-Blodgett monolayers in the presence and absence of melittin, which eventually allows characterization of the melittin-induced pores at a quantitative low-resolution level. We observed that the large majority of pores exhibit near-circular symmetry and a Gaussian distribution in size, with a mean diameter of ∼8.7 nm. A distinctive feature is a ring of material found around the pores, made by, on average, three positive peaks, with a height over the level of the lipidic background of ∼0.23 nm. This protruding rim is most likely due to the presence of melittin near the pore border. Although the current resolution of the AFM images in the {x, y} plane does not allow distinction of the specific organization of the peptide molecules, these results provide an unprecedented view of melittin pores formed in lipidic interfaces and open new perspectives for future structural investigations of these and other pore-forming peptides and proteins using supported monolayers.

Probing the interactions of mitoxantrone with biomimetic membranes with electrochemical and spectroscopic techniques

Mitoxantrone – an anticancer drug – was used to probe the interactions of this class of cytostatic molecules with biomimetic monolayers. The drug effect was monitored with electrochemical (cyclic voltammetry and electrochemical impedance spectroscopy), as well as spectroscopic techniques (surface enhanced Raman scattering), during its passive partitioning/penetration through the mixed Langmuir and Langmuir–Blodgett monolayers after their transfer on gold electrodes. This approach allowed us to discriminate between the drug interactions with hydrophilic head-group region and hydrophobic alkyl chains moiety of such monolayers.

Probing the Anisotropy of SERS Enhancement with Spatially Separated Plasmonic Modes in Strongly Coupled Silver Nanocubes on a Dielectric Substrate

The utilization of substrate–particle interactions provides a route to tuning the optical properties of strongly coupled supported plasmonic nanoparticles. In this work fine control over interparticle and particle–substrate interactions is demonstrated using Langmuir–Blodgett monolayers of silver nanocubes deposited onto titanium oxide (TiOx) thin films of varying thickness. By using two Raman reporters, a Rhodamine-B (RhB) and benzenethiol (BT), surface-enhanced Raman spectroscopy (SERS) independently examines electromagnetic (EM) enhancement at the substrate/nanocube interface (RhB) and at the surface of the cubes, where the label is predominately 20–40 nm away from the dielectric substrate (BT). For RhB the SERS enhancement factor (EF) drops as much as an order of magnitude on 20 nm TiOx with respect to glass. However, for BT, a maximum SERS EF of (2.5 ± 0.4) × 105 was observed on TiOx compared to (1.5 ± 0.4) × 105 on glass, an increase of 60%. Control over the organization of the nanocube monolayer re...

Atomic force microscopy and Langmuir–Blodgett monolayer technique to assess contact lens deposits and human meibum extracts

PurposeThe purpose of this exploratory study was to investigate the differences in meibomian gland secretions, contact lens (CL) lipid extracts, and CL surface topography between participants with and without meibomian gland dysfunction (MGD). MethodsMeibum study: Meibum was collected from all participants and studied via Langmuir–Blodgett (LB) deposition with subsequent Atomic Force Microscopy (AFM) visualization and surface roughness analysis. CL Study: Participants with and without MGD wore both etafilcon A and balafilcon A CLs in two different phases. CL lipid deposits were extracted and analyzed using pressure-area isotherms with the LB trough and CL surface topographies and roughness values were visualized using AFM. ResultsMeibum study: Non-MGD participant meibum samples showed larger, circular aggregates with lower surface roughness, whereas meibum samples from participants with MGD showed more lipid aggregates, greater size variability and higher surface roughness. CL Study: Worn CLs from participants with MGD had a few large tear film deposits with lower surface roughness, whereas non-MGD participant-worn lenses had many small lens deposits with higher surface roughness. Balafilcon A pore depths were shallower in MGD participant worn lenses when compared to non-MGD participant lenses. Isotherms of CL lipid extracts from MGD and non-MGD participants showed a seamless rise in surface pressure as area decreased; however, extracts from the two different lens materials produced different isotherms. ConclusionsMGD and non-MGD participant-worn CL deposition were found to differ in type, amount, and pattern of lens deposits. Lipids from MGD participants deposited irregularly whereas lipids from non-MGD participants showed more uniformity.

Langmuir-Blodgett Films of Gold Nanorods with Different Silica Shell Thicknesses

We report the preparation and optical characterization of Langmuir and Langmuir-Blodgett (LB) films of mesoporous silica coated gold nanorods with three different shell thicknesses. When measured in solution, the extinction of the particles in the short wavelength region becomes dominated by light scattering with increasing shell thickness. Due to the silica shell, however, it is possible to prepare continuous Langmuir and Langmuir-Blodgett monolayers of the particles over macroscopic areas. To investigate the role of the gold core and the silica coating in the optical properties of the monolayers, reflection measurements in combination with thin-film optical modeling were carried out. Interestingly, the optical behavior of the Si deposited LB monolayers is mainly governed by the silica shell: the reflection spectrum is dominated by thin-film interference instead of the localized surface plasmon resonance peaks. This is in agreement with our earlier results obtained for core-free plain silica nanoparticle LB monolayers.

Effect of Central Metals on Langmuir-Blodgett Monolayers of Phthalocyanines with Flexible Substituents

Effect of Central Metals on Langmuir-Blodgett Monolayers of Phthalocyanines with Flexible Substituents

Monolayers Langmuir-Blodgett Films of Synthetic Artificial Mimic Molecules That Resemble the Following Tetraether Lipids on Silicon Wafers

This study investigated the behavior and molecular organization of synthetic artificial mimic molecules that resemble the following tetraether lipids: di-O-hexadecyl-glycero-3-phosphatidyl-glycerol (DHGPG) and bis-4-dodecylphenyl-12-phosphate. These molecules were analyzed using Langmuir film balance, ellipsometry and atomic force microscopy. The monolayer Langmuir-Blodgett films of DHGPG and bis-4-dodecylphenyl-12-phosphate were stable on the solid surface silicon wafers. The ellipsometry and AFM results showed that monolayers Langmuir-Blodgett films of DHGPG and bis-4-dodecylphenyl-12-phosphate were present, and the thickness of the observed films varied from 1.2 - 5.0 nm.

Single Gold Atom Containing Oligo(phenylene)ethynylene: Assembly into LB Films and Electrical Characterization

Monomolecular films of an oligo(phenylene)ethynylene, OPE, derivative [2-isocyano-1,3-dimethylbenzene][4-(4′-aminophenylethynyl)phenylethynyl]gold, 1, containing a gold atom in the molecule backbone have been prepared by the Langmuir–Blodgett (LB) method in order to study how the electrical properties can be modulated in monolayers of OPEs by incorporation of a gold center in their structures. UV–vis reflection spectra of Langmuir monolayers of 1 at the air–water interface reveal strong aurophilic interactions between neighboring molecules that increase upon compression. Monolayer Langmuir–Blodgett (LB) films were readily fabricated by the transfer of Langmuir films of 1 onto solid substrates. Quartz crystal microbalance (QCM) experiments conclusively demonstrate formation of monolayer LB films with a high surface coverage. The morphology of these films was analyzed by atomic force microscopy (AFM), revealing formation of homogeneous layers with an optimum surface pressure of transference of 6 mN·m–1. Fil...

Easily processable highly ordered Langmuir-Blodgett films of quaterthiophene disiloxane dimer for monolayer organic field-effect transistors.

Self-assembly of highly soluble water-stable tetramethyldisiloxane-based dimer of α,α'-dialkylquaterthiophene on the water-air interface was investigated by Langmuir, grazing incidence X-ray diffraction, and X-ray reflectivity techniques. The conditions for formation of very homogeneous crystalline monolayer Langmuir-Blodgett (LB) films of the oligomer were found. Monolayer organic field-effect transistors (OFETs) based on these LB films as a semiconducting layer showed hole mobilities up to 3 × 10(-3) cm(2)/(V s), on-off ratio of 10(5), small hysteresis, and high long-term stability. The electrical performance of the LB films studied is close to that for the same material in the bulk or in the monolayer OFETs prepared from water vapor sensitive chlorosilyl derivatives of quaterthiophene by self-assembling from solution. These findings show high potential of disiloxane-based LB films in monolayer OFETs for large-area organic electronics.

Ar+ ion irradiation-induced reorganization of colloidal silica nanoparticles in Langmuir–Blodgett monolayers

The Ar+ ion irradiation-induced reorganization of Langmuir–Blodgett monolayers of colloidal silica nanoparticles with a diameter of 220nm and 450nm deposited on silicon substrate is investigated in a wide range of ion fluences. The cluster formation, average cluster size, ion beam-induced charging and discharging of particles, heating effects, the ion beam-induced viscous flow as well as the swelling of the Si substrate as a function of the ion fluence are discussed. Inhomogeneous particle distribution causes strong nonlinear Si swelling inside wide defect-channels between the clusters and linear Si swelling inside narrow channels between the particles. At low ion fluences particle charging and Coulomb repulsion forces govern the particle reorganization process, while at high ion fluences ion beam-induced viscous flow and hydrodynamic forces between the particles and the underlying substrate play major role. Two different types of patterns: smaller compact clusters of few particles and longer chain-like clusters of dozens of particles are observed. The dynamics of the reorganization process in both cases is treated analogous to the dynamics of colloidal suspensions based on the Tanaka–Araki model. The results of the model are comparable to the experimentally observed cluster characteristics.

Characterization of 10,12-pentacosadiynoic acid Langmuir-Blodgett monolayers and their use in metal-insulator-metal tunnel devices.

The characterization of Langmuir–Blodgett thin films of 10,12-pentacosadiynoic acid (PDA) and their use in metal–insulator–metal (MIM) devices were studied. The Langmuir monolayer behavior of the PDA film was studied at the air/water interface using surface tension–area isotherms of polymeric and monomeric PDA. Langmuir–Blodgett (LB, vertical deposition) and Langmuir–Schaefer (LS, horizontal deposition) techniques were used to deposit the PDA film on various substrates (glass, quartz, silicon, and nickel-coated film on glass). The electrochemical, electrical and optical properties of the LB and LS PDA films were studied using cyclic voltammetry, current–voltage characteristics (I–V), and UV–vis and FTIR spectroscopies. Atomic force microscopy measurements were performed in order to analyze the surface morphology and roughness of the films. A MIM tunnel diode was fabricated using a PDA monolayer assembly as the insulating barrier, which was sandwiched between two nickel layers. The precise control of the thickness of the insulating monolayers proved critical for electron tunneling to take place in the MIM structure. The current–voltage characteristics of the MIM diode revealed tunneling behavior in the fabricated Ni–PDA LB film–Ni structures.

The Mechanisms of Rectification in Au|Molecule|Au Devices Based on Langmuir–Blodgett Monolayers of Iron(III) and Copper(II) Surfactants

AbstractLangmuir–Blodgett films of metallosurfactants were used in Au|molecule|Au devices to investigate the mechanisms of current rectification.

The mechanisms of rectification in Au|molecule|Au devices based on Langmuir-Blodgett monolayers of iron(III) and copper(II) surfactants.

Langmuir-Blodgett films of metallosurfactants were used in Au|molecule|Au devices to investigate the mechanisms of current rectification.

Silicon sensitisation using light harvesting layers

Langmuir–Blodgett monolayers of a cyanine dye mixed with stearic acid were deposited on glass and silicon substrates with spacer layers of pure stearic acid monolayers or silicon dioxide films deposited by PECVD. By using the time correlated single photon counting technique, time resolved emission spectra (TRES) and decay curves were measured to characterise the dependence of energy transfer rate on the separation between the dye monolayer and the silicon surface and also for the dye concentrations in the monolayers. We observe interlayer energy transfer between monomers, dimers and higher aggregates present in the monolayer deposited on glass but also competing directly with energy transfer to silicon at close distances. We find that the fluorescence lifetime of the dye monolayer is significantly shortened when deposited close to the silicon surface signifying efficient energy transfer. The dissipation of the excitation energy near silicon is explained using the classical theory developed for metals and a deviation is observed for monolayers deposited at distances close to the silicon surface.