Langmuir-Blodgett Technique Research Articles

Chiral Porphyrin Assemblies: From Solution to Solid State

Chirality has increasingly nurtured scientific interests because, beyond the concepts related with the emergence and evolution of Life, it has remarkable implications in practical fields, where chiral materials, coupled with nanotechnology, can be exploited in chiral sensing, optical displays, information storage, asymmetric catalysis and so on.Porphyrins have been extensively used as building blocks to assembling organized systems featuring chirality at supramolecular level, mostly in solution. Indeed, the fine tuning of the properties of these chiral systems, is made possible by a florilegium of either internal or external stimuli, such as solvent polarity, pH, ionic strength, and templates.1 Although the achievement in solution is now well-established, the transfer of the chiral assemblies from solution to thin-film onto inorganic surfaces is not so obvious. Indeed, outside factors as hydrophilic/hydrophobic character of the substrates or the solvent evaporation process can deeply influence film formation and, consequently, its chirality. Furthermore, multiple limitations concerning, among others, robustness and versatility of the chiral nanostructures has still to be overcome for their efficient real-life implementation in a device.Over the years, we investigated the construction of chiral aggregates based on prolinated porphyrin derivatives in hydroalcoholic mixtures, whose formation was steered by hydrophobic effect. We demonstrated the influence of structural parameters (metal coordinated, charge/stereochemistry of the proline moiety) as well as solvent bulk properties (composition, concentration, ionic strength, presence of co-solutes) on both the overall aggregation process and the final morphologies observed.2-4 The implementation on a device often requires the fabrication of solid film by varied controlled deposition techniques able to maintain/amplify the chiral features of the aggregates formed in solution or to create ordered chiral layers by symmetry breaking events (i.e. Langmuir Blodgett or Langmuir-Schaefer techniques). Porphyrin derivatives bearing an appended (L)- or (D)- functionality on a meso phenyl position offered multiple options for realizing chiral surfaces, which are illustrated in Figure 1. Indeed, chiral films can be obtained by drop casting the aggregates formed in EtOH/H2O mixtures on glass, as well as a toluene solution of the porphyrin monomers. Alternatively, the carboxylic group placed on the proline unit can be exploited to anchor the macrocycle onto different inorganic nanostructures, as ZnO or silica nanoparticles, giving chiral layers on glass or quartz slides. In this regard, we also recently found that hybrid systems constituted by chiral Zn-porphyrin capped ZnO nanostructures are able to selectively detect the different enantiomers of chiral analytes, such as limonene vapours, when layered on quartz microbalance surface.5 The potential use of these chiral systems as sensitive materials in stereoselective sensors is indeed particularly appealing, since the most of new emergent pollutants released into the environment by pharmaceutical or agrochemical industries are chiral compounds, whose biological impact strictly depends on the specific enantiomer.In this contribution, an overview of the different preparation protocols of chiral porphyrin-based films will be provided, thoroughly illustrating the characterization of the obtained surfaces by several microscopies and spectroscopic investigations. Furthermore, studies on the chiral discrimination potential featured by the developed surfaces will be also presented. Figure 1

Hybrid System for Local Drug Delivery and Magnetic Hyperthermia Based on SPIONs Loaded with Doxorubicin and Epirubicin.

Cancer is one of the most common causes of death worldwide, thus new solutions in anticancer therapies are highly sought after. In this work, superparamagnetic iron oxide nanoparticles (SPIONs) conjugated with anticancer drugs are synthesized and investigated as potential magnetic drug nanocarriers for local drug delivery and mild magnetic hyperthermia. We have obtained a hybrid system loaded with holmium and anticancer drugs and thoroughly studied it with respect to the size, morphology, surface modifications and magnetic properties, and interactions with the model of biological membranes, cytotoxicity. We present that nanoparticles having a round shape and size 15 nm are successfully stabilized to avoid their agglomeration and modified with doxorubicin or epirubicin within a controlled way. The number of drugs loaded into the SPIONs was confirmed with thermogravimetry. The hybrid based on SPIONs was investigated in touch with model biological membranes within the Langmuir-Blodgett technique, and results show that modified SPION interacts effectively with them. Results obtained with magnetic hyperthermia and biological studies confirm the promising properties of the hybrid towards future cancer cell treatment.

Frequency- and magnetic-field-dependent properties of ordered magnetic nanoparticle arrangements

We present investigations of the frequency and magnetic field dependent properties of ordered magnetic nanoparticles (MNPs) arrangements consisting of magnetite (${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$) nanoparticles with an average diameter of 20 nm by employing micro Brillouin light scattering microscopy. We utilized electron beam lithography to prepare hexagonally arranged, circularly shaped MNP assemblies consisting of a single layer of MNPs using a variant of the Langmuir-Blodgett technique. By comparing the results with nonstructured, layered superlattices of MNPs, further insight into the influence of size and geometry of the arrangement on the collective magnetic properties is obtained. We show that at low static external field strengths, two signals occur in frequency dependent measurements for both nonstructured and structured assemblies. Increasing the static external field strength results in a sharpening of the main signal, while the satellite signal decreases in its intensity and increases in its linewidth. The occurrence of multiple signals at low external field strengths is also confirmed by sweeping the static external field and keeping the excitation frequency constant. Furthermore, two-dimensional spatial mapping of the resonances reveals that the main and the satellite signal originate from the center and the edge, respectively, of a single circular MNP assembly. Micromagnetic simulations confirm these assignments and the dependence of the two signals on the static external field strength, justifying an interpretation of the observed characteristics in terms of different local environments of MNPs forming the MNP assembly.

Studies the interactions of ascorbic acid isoforms with a simple model of DPPC monolayer as a biomimetic membrane by Langmuir-Blodgett technique

There is ongoing interest motivated by the desire regarding monolayer to understand the nature of interaction forces within oriented structures. Monolayer of phospholipids dipalmitoylphosphatidylcholine DPPC were examined mainly because they are accepted as membrane model system and can offer a stable frame to investigate the interactions of various biomolecules and biomaterial compounds with the lipid membrane. Identifying the monolayer behavior in the presence of ascorbic acid (AscA) isoforms and if this isoforms could alter packing and organizing the thin film. By Langmuir-Blodgett technique, the DPPC monolayer were studied in absence and presence of (Conc.: 10−3M, 10−2M and 10−1M) L- and D- AscA isoforms in water (subphase) at temperatures 25, 37 and 41°C and fixed pH=7. It’s ascertained in this study that, the subphase with L- and D-AscA addition created a fixed monolayer at 25°C, while at high temperature 41°C causes alteration in DPPC monolayer to somewhat less densely pack especially L-AscA this is for instance disclosed by left-area shifted of the DPPC monolayer curve shape. The Langmuir monolayer studies revealed that AscA isoforms interrupt the DPPC monolayer during its formation, leads to make the variations in such monolayers properties. This work demonstrates that AscA addition in subphase has applied promising significant disturbing in monolayer play an essential role in biomimetic membrane.

Deposition of Extended Ordered Ultrathin Films of Au38 (SC2 H4 Ph)24 Nanocluster using Langmuir-Blodgett Technique.

Langmuir-Blodgett technique is utilized to deposit ultrathin films of Au38 (SC2 H4 Ph)24 nanocluster onto solid surfaces such as mica and silicon. Themorphologies of the films transferred at various surface pressures within the mono/bi/trilayer regime are studied by atomic force microscopy (AFM). The time spent on the water surface before the deposition has a decisive effect on the final ordering of nanoclusters within the network and is studied by fast AFM, X-ray reflectivity, and grazing-incidence wide-angle X-ray scattering.

Large-area atomic-smooth polyvinylidene fluoride Langmuir-Blodgett film exhibiting significantly improved ferroelectric and piezoelectric responses

Large roughness and structure disorder in ferroelectric ultrathin Langmuir-Blodgett (LB) film results in severe space scatter in electrical, ferroelectric and piezoelectric characteristics, thus limiting the nanoscale research and reliability of nano-devices. However, no effective method aiming at large-area uniform organic ferroelectric LB film has ever been reported to date. Herein, we present a facile hot-pressing strategy to prepare relatively large-area poly(vinylidene fluoride) (PVDF) LB film with ultra-smooth surface root mean square (RMS) roughness is 0.3 nm in a 30 μm × 30 μm area comparable to that of metal substrate, which maximized the potential of LB technique to control thickness distribution. More importantly, compared with traditionally annealed LB film, the hot-pressed LB film manifests significantly improved structure uniformity, less fluctuation in ferroelectric characteristics and higher dielectric and piezoelectric responses, owing to the uniform dipole orientation and higher crystalline quality. Besides, different surface charge relaxation behaviors are investigated and the underlying mechanisms are explained in the light of the interplay of surface charge and polarization charge in the case of nanoscale non-uniform switching. We believe that our work not only presents a novel strategy to endow PVDF LB film with unprecedented reliability and improved performance as a competitive candidate for future ferroelectric tunnel junctions (FTJs) and nano electro mechanical systems (NEMS), but also reveals an attracting coupling effect between the surface potential distribution and nanoscale non-uniform switching behavior, which is crucial for the understanding of local transport characterization modulated by band structure, bit signal stability for data-storage application and the related surface charge research, such as charge gradient microscopy (CGM) based on the collection of surface charge on the biased ferroelectric domains.

Zinc oxide nanocolumns grown on self-assembled silica nanosphere monolayer templates

This paper presents a concept of a two-step growth process that first lays down a nano template by self-assembly to define the spatial distribution of the nanostructures, followed by a highly directional physical vapor deposition method to selectively grow material in a columnar configuration. Langmuir–Blodgett technique was used to construct self-assembled monolayers of silica nanospheres (SNSs) with five different radii, 1.9 μm, 590 nm, 425 nm, 250 nm, and 125 nm. Z-axis oriented ZnO crystalline nanostructures grown on top of the spheres by the Glancing Angle PLD formed columnar arrays that were observed to form a hcp structure. Columnar aspect ratios as well as the density per unit area were found to be dependent on underlying sphere size. In addition to the experimental demonstration of the technique, a nucleation model is presented to understand the mechanism of growth in this novel approach.

Coating of Conducting and Insulating Threads with Porous MOF Particles through Langmuir-Blodgett Technique.

The Langmuir-Blodgett (LB) method is a well-known deposition technique for the fabrication of ordered monolayer and multilayer thin films of nanomaterials onto different substrates that plays a critical role in the development of functional devices for various applications. This paper describes detailed studies about the best coating configuration for nanoparticles of a porous metal-organic framework (MOF) onto both insulating or conductive threads and nylon fiber. We design and fabricate customized polymethylmethacrylate sheets (PMMA) holders to deposit MOF layers onto the threads or fiber using the LB technique. Two different orientations, namely, horizontal and vertical, are used to deposit MIL-96(Al) monolayer films onto five different types of threads and nylon fiber. These studies show that LB film formation strongly depends on deposition orientation and the type of threads or fiber. Among all the samples tested, cotton thread and nylon fiber with vertical deposition show more homogenous monolayer coverage. In the case of conductive threads, the MOF particles tend to aggregate between the conductive thread’s fibers instead of forming a continuous monolayer coating. Our results show a significant contribution in terms of MOF monolayer deposition onto single fiber and threads that will contribute to the fabrication of single fiber or thread-based devices in the future.

Photosensitive Thin Films Based on Drop Cast and Langmuir-Blodgett Hydrophilic and Hydrophobic CdS Nanoparticles.

Comparative photoelectrochemical studies of cadmium sulfide (CdS) nanoparticles with either hydrophilic or hydrophobic surface properties are presented. Oleylamine organic shells provided CdS nanoparticles with hydrophobic behavior, affecting the photoelectrochemical properties of such nanostructured semiconductor. Hydrophilic CdS nanoparticles were drop-cast on the electrode, whereas the hydrophobic ones were transferred in a controlled manner with Langmuir-Blodgett technique. The substantial hindrance of photopotential and photocurrent was observed for L-B CdS films as compared to the hydrophilic, uncoated nanoparticles that were drop-cast directly on the electrode surface. The electron lifetime in both hydrophilic and hydrophobic nanocrystalline CdS was determined, revealing longer carrier lifetime for oleylamine coated CdS nanoparticles, ascribed to the trapping of charge at the interface of the organic shell/CdS nanoparticle and to the dominant influence of the resistance of the organic shell against the flux of charges. The “on” transients of the photocurrent responses, observed only for the oleylamine-coated nanoparticles, were resolved, yielding the potential-dependent rate constants of the redox processes occurring at the interface.

100 °C-Langmuir–Blodgett Method for Fabricating Highly Oriented, Ultrathin Films of Polymeric Semiconductors

The Langmuir-Blodgett (LB) and Langmuir-Schaefer techniques facilitate thermodynamic favorability at an air-water interface, at which nanoscale molecular aggregations can be manipulated by micrometer- or millimeter-scale mechanics. The customary use of an aqueous subphase has limitations in the available temperature and spread materials. We present a general strategy to replace the aqueous subphase with an inert, low-vapor-pressure liquid, ethylene glycol. As a representative spread material that requires high-temperature processes, a semicrystalline polymeric semiconductor was investigated. We successfully demonstrated that the polymeric semiconductor spreads homogeneously across the entire surface of ethylene glycol heated to 100 °C using an LB trough, and spontaneously forms multilayers. Comprehensive studies such as X-ray diffraction, optical spectroscopy, and charge transport measurements revealed that barrier compression of solid-state polymer thin films during a high-temperature LB process produced uniaxial alignment of the polymer main chain with an averaged dichroic ratio of about 8, by which the electron transport concomitantly became highly anisotropic. The LB method presented in this work could be used to deposit thin films under ultimate environments, e.g., below 0 °C or above 100 °C, minimizing the effects of the vapor pressure of the subphase.

Intrinsic Magnetic Order of Chemically Exfoliated 2D Ruddlesden-Popper Organic-Inorganic Halide Perovskite Ultrathin Films.

Thin film fabrication of 2D layered organic-inorganic hybrid perovskites (2D-OIHPs) for spintronic applications has been attempted using solution-based process like Langmuir-Blodgett technique. However, monolayer or few-layered 2D magnets are not yet realized, even though a wide spectrum of 2D Ruddlesden-Popper (RP) OIHPs are known as quasi-2D Heisenberg magnets in bulk compounds. Here, chemical exfoliation by solvent engineering is applied to successfully synthesize large-sized, few unit-cell-thick 2D RP-OIHPs. Comprehensive structural characterization reveals that binary co-solvents with high relative polarity in spin coating technique are the most effective among nine kinds of solvents. Above all, this enables few-layered 2D RP-OIHP ultrathin films sustaining their intrinsic magnetic order. It is found that XY-like magnetic anisotropy driven by Jahn-Teller effect responsible for ferromagnetism in seven-layered (C6 H5 CH2 CH2 NH3 )2 CuCl4 ultrathin films remains very robust, whereas Ising-like dipolar anisotropy responsible for canted antiferromagnetism in ten-layered (C6 H5 CH2 CH2 NH3 )2 MnCl4 ultrathin films is greatly reduced. It is expected that ferromagnetism even at monolayer limit should be possible by means of further sophisticated solvent engineering as long as Jahn-Teller effect is active. The chemical exfoliation using solvent engineering unambiguously can bring about a new breakthrough in the development of 2D RP-OIHP van der Waals magnets for ultrahigh energy-efficient spintronic, opto-spintronic devices.

Optimizing Gold Nanoparticle Size and Shape for the Fabrication of SERS Substrates by Means of the Langmuir-Blodgett Technique.

The Langmuir–Blodgett technique, in which a layer of nanoparticles is spread at the water/air interface and further transferred onto a solid support, is a versatile approach for the preparation of SERS substrates with a controllable arrangement of hotspots. In a previous work, we demonstrated that fine-tuning the lateral packing and subsequent seed growth of 10 nm gold nanoparticles led to a quasi-resonant enhanced in the SERS signal of a test analyte. Here, we explore further enhancements by modifying the size and shape of the spread gold nanoparticles in order to take advantage of the inherent interparticle repulsion mechanisms present at the interface. We show that the size of the used nanoparticles is also a determinant factor, which cannot be compensated by the subsequent electroless growth. We also show that, although the seeded growth leads to rough hotspots, the sensitivity can be optimized by self-assembling urchin-shaped nanoparticles, with a roughness that is fine-tuned a priori. Our results suggest an intriguing correlation between surface homogeneity and SERS signal enhancement, indicating that regular substrates will have the optimal performance.

Langmuir Films of Perfluorinated Fatty Alcohols: Evidence of Spontaneous Formation of Solid Aggregates at Zero Surface Pressure and Very Low Surface Density.

In this work, Langmuir films of two highly fluorinated fatty alcohols, CF3(CF2)12CH2OH (F14OH) and CF3(CF2)16CH2OH (F18OH), were studied. Atomic Force Microscopy (AFM) images of the films transferred at zero surface pressure and low surface density onto the surface of silicon wafers by the Langmuir-Blodgett technique revealed, for the first time, the existence of solid-like domains with well-defined mostly hexagonal (starry) shapes in the case of F18OH, and with an entangled structure of threads in the case of F14OH. A (20:80) molar mixture of the two alcohols displayed a surprising combination of the two patterns: hexagonal domains surrounded by zigzagging threads, clearly demonstrating that the two alcohols segregate during the 2D crystallization process. Grazing Incidence X-ray Diffraction (GIXD) measurements confirmed that the molecules of both alcohols organize in 2D hexagonal lattices. Atomistic Molecular Dynamics (MD) simulations provide a visualization of the structure of the domains and allow a molecular-level interpretation of the experimental observations. The simulation results clearly showed that perfluorinated alcohols have an intrinsic tendency to aggregate, even at very low surface density. The formed domains are highly organized compared to those of hydrogenated alcohols with similar chain length. Very probably, this tendency is a consequence of the characteristic stiffness of the perfluorinated chains. The diffraction spectrum calculated from the simulation trajectories compares favorably with the experimental spectra, fully validating the simulations and the proposed interpretation. The present results highlight for the first time an inherent tendency of perfluorinated chains to aggregate, even at very low surface density, forming highly organized 2D structures. We believe these findings are important to fully understand related phenomena, such as the formation of hemi-micelles of semifluorinated alkanes at the surface of water and the 2D segregation in mixed Langmuir films of hydrogenated and fluorinated fatty acids.

Clustering Artificial Atoms Induced by High-Frequency Electromagnetic Radiation in Graphene Monolayers of Multiwalled Carbon Nanotubes

A graphene-charge carrier confinement induced by high-frequency photons and a subsequent clustering of artificial atoms in graphene plane have been studied using electrophysical and Raman-spectroscopy methods. To fabricate the graphene n-p-n junctions, commensurable superlattice structures consisting of multi-walled carbon nanotubes (MWCNTs) have been formed utilizing a Langmuir-Blodgett technique. It has been shown that the p-n graphene junctions are sensitive to graphene lattice-deformation defects only. The levels of graphene defect do not host impurity electrons. One offers a mechanism of graphene monolayer self-repairing after a radiation damage. This mechanism is based on an existence of topologically protected Compton scatterers in graphene plane.

Development of a Schottky barrier diode using molecular network of 1-alkyl-2-(arylazo) imidazole prepared by Langmuir–Blodgett technique

In this paper we report the photophysical and electrical characteristics of our synthesized imidazole derivative namely l-alkyl-2-(arylazo) imidazole (AAI) organized in Langmuir-Blodgett (LB) films towards the development of organic Schottky barrier diode (SBD). Presence of long alkyl chain in the molecule make it suitable for LB technology and may favour aggregations of the molecules in LB films under barrier compression. The interfacial properties of the formation of Langmuir monolayer of AAI at air-water interface have been studied by surface pressure versus area per molecule (π-A) isotherm and compressibility modulus. Hysteresis study of the isotherm confirmed the formation of stable monolayer of AAI molecular assemblies at air-water interface. The aggregation of AAI molecules in LB films is confirmed by Ultraviolet–visible (UV–vis) absorption, fluorescence emission spectroscopy and Atomic force microscopic (AFM) methods. AAI molecules also formed network type morphology in LB films due to their closure association and aggregations or cluster of molecules which were evidenced by AFM technique. The compression induced aggregations of AAI is reflected as broadened nature of monomeric absorption band along with the emergence of a new absorption band at longer wavelength side for LB film deposited at surface pressure of 25 mN/m. The optical absorption bands of AAI and the corresponding transitions between different electronic states have been simulated by density functional theoretical (DFT) analysis and is compared with the experimental results. Nonlinear behaviour of the current-voltage characteristics and various relevant electrical parameters of the LB film device at the interface of metal electrode (gold) satisfy the necessary conditions showing the properties of a Schottky barrier diode.

Properties of DNA-CTMA monolayers obtained by Langmuir-Blodgett technique

The complex consisting of DNA and cetyltrimethylammonium chloride (DNA-CTMA) is extensively exploited in organic electronics in form of thin films with submicron or nanometer thickness. In this work, using the Langmuir-Blodgett technique, the surface films were prepared from complexes based on different types of chromosomal and plasmid DNA. The research focused on changes in their continuity after they were transferred onto a solid substrate. It was found that only the monolayer of plasmid DNA-CTMA complex remained continuous after being transferred. The other complexes underwent a spontaneous self-assembling and created elongated linear patterns. AFM images of these patterns were analysed quantitatively with Fast Fourier Transform. It was confirmed that self-assembling occurred along one privileged direction.

Thickness dependence of nanocrystalline tin oxide thin films in capacitive biosensor characterization

Nanocrystalline SnO2 thin films of varying thicknesses (250–50 nm) have been prepared on p-type Si by Langmuir Blodgett technique. Nanocrystalline SnO2/polyaniline (Si/SnO2/PANI) thin film heterostructure has been studied for label free, real time electrochemical detection for model immunoglobulin interactions. Sensor responses were studied using impedance methods, wherein transient capacitance gave fast response for antigen-antibody interaction in picomolar concentration range. From the study of sensor structures with varying film thicknesses, it was observed that SnO2 film with less than 200 nm thickness were effected with insulating (dielectric) properties whereas for thickness higher than 200 nm, it was n-type semiconducting characteristics. This is due to effects of charge on the surface adsorbed species as revealed by capacitance voltage characteristics, suggesting these characteristics as indicators of ionic transport effects in nanostructured metal oxide films in electrochemical cell configuration. The current study clearly states the possibility of fabricating cost effective and stable capacitive sensors with SnO2 films with thickness less than 100 nm. The study helps in optimizing the sensing method for capacitive/conductive biosensors based on nanostructured semiconductor thin films.

Helicity Manipulation of a Double-Paddled Binaphthyl in a Two-Dimensional Matrix Field at the Air-Water Interface.

Molecular behavior and functionality are affected by their prevailing immediate environment. Molecular machines function according to conformational variations and have been studied largely in solution states. In order to access more highly complex functional molecular machines, it is necessary to analyze and control them in various environments. We have designed and synthesized a bisbinaphthyldurene (BBD) molecule that has two binaphthyl groups connected through a central durene moiety, allowing for the formation of several conformers. In density functional theory (DFT) calculations, BBD has five major conformers, denoted anti-1/anti-2/syn-1/syn-2/flat. It has been demonstrated that BBD exhibits different conformations in solution (anti-1 and syn-1) than on a gold surface (syn dimer and flat). In this work, the ratio of BBD conformations has been controlled in mixed monolayers with several different lipids at an air-water interface in order to compare conformational activity under different conditions. The conformations of BBD in transferred films obtained by using Langmuir-Blodgett techniques were estimated from circular dichroism spectra and DFT calculations. It has been found that the conformation of BBD in the mixed monolayer depends on its aggregated state, which has been controlled here by the mechanical properties and miscibility. In mixed monolayers with "hard" lipids having less miscibility with BBD as well as in cast film, BBD is self-aggregated and mostly forms stable anti-1 and syn-1 conformations, while unstable anti-2 and syn-2 conformers dominated in the more dispersed states involving "soft" lipids, which show good miscibility with BBD. Conformational changes in BBD are due to the formation of different aggregated states in each mixed monolayer according to the miscibility. Overall, BBD molecular conformations (and the resulting spectra) could be tuned by controlling the environment whether in solution, on a solid substrate, or in an admixture with lipids at the air-water interface.

Graphenic substrates as modifiers of the emission and vibrational responses of interacting molecules: The case of BODIPY dyes.

Graphenic substrates (GS), such as reduced graphene oxide (rGO) and graphene oxide (GO), are 2D materials known for their unique physicochemical properties such as their ability to enhance vibrational spectroscopic signals and quench the fluorescence of adsorbed molecules. These properties provide an opportunity to develop nanostructured GS-based systems for detecting and identifying different analytes with high sensitivity and reliability through molecular spectroscopic techniques. This work evaluated the capacities of different GS to interact with a highly fluorescent compound, thereby changing its optical emission response (fluorescence quenching) and amplifying its vibrational signal, which is the base of graphene-enhanced Raman scattering (GERS). To test these properties, we used a derivative of highly fluorescent BODIPY (BP) compounds, which cover a wide range of applications from solar energy conversion to photodynamic cancer therapy. GS prepared by using the Langmuir-Blodgett (LB) technique allowed us to quench the fluorescence emission of BP and improve its Raman spectroscopy detection limit due to the GERS effect. These results were interpreted in light of the π-π interactions taking place between the Csp2 domains of GS and the aromatic core of the BP fluorophore.

Electrowetting on Langmuir-Blodgett films from epicuticular wax

Langmuir and Langmuir-Blodgett (LB) films were fabricated from epicuticular wax, that had been extracted from Vitis vinifera. For Langmuir films, the influence of subphase temperature on their structure was examined, whereas for LB films, the surface morphology at various temperatures and the effect of the layer number on electrowetting were investigated. Isotherms of surface pressure revealed no well-defined phase transition or collapse on Langmuir films at 22 °C, whereas Brewster angle microscopy showed that even before starting the compression procedure, there are platelets of epicuticular wax floating on the subphase. Those platelets give rise to the Langmuir films of epicuticular wax during compression. In contrast, for higher temperatures (40 °C and 50 °C), a well-defined phase transition was found – without epicuticular wax platelets, with a behavior close to those found in typical fatty acids. For LB films, atomic force microscopy images indicated a decreasing of roughness as a function of the subphase temperature as a result of greater organization of the epicuticular wax film. A significant modulation of about 20 ° (under applied voltage range of 0 to 100 V) was demonstrated of the electrowetting on LB films, which did not depend on the LB layer number. Our results suggest that epicuticular wax LB films have the potential for being applied in electrowetting-based devices. Furthermore, the Langmuir-Blodgett technique is feasible to fabricate films with various compositions focusing on the electrowetting.