Blodgett Technique Research Articles

Nanoparticle‐Imprinted Polymers: Shell‐Selective Recognition of Au Nanoparticles by Imprinting Using the Langmuir–Blodgett Method

AbstractSpeciation of nanoparticles, that is, their differentiation based on size, shape and stabilizing shell is becoming important since their properties depend on these parameters. Nanoparticle‐imprinted polymers (NIPs) are a new approach that aims to selectively recognize nanoparticles based on their structural properties. In this study, monolayers of cellulose acetate (CA) accommodating gold nanoparticles stabilized with dodecanethiol (AuNPs/C12) are transferred onto indium tin oxide (ITO) by the Langmuir–Blodgett technique. One to five monolayers are assembled. Electrochemical oxidation dissolves the AuNPs/C12 to form cavities in the films, which fit the size and shape of the AuNPs/C12. Reuptake of the nanoparticles from a solution is successful using the imprinted films, whereas the control films containing only CA layers do not reuptake the AuNPs/C12. The NIPs are highly selective and other gold nanoparticles stabilized by other thiols are not recognized by the imprinted matrix.

Light-responsive plasmonic arrays consisting of silver nanocubes and a photoisomerizable matrix.

We report on the synthesis of novel branched organic-inorganic azo-polyhedral oligomeric silsesquioxane (POSS) conjugates (Azo-POSS) and their use as a stable active medium to induce reversible plasmonic modulations of embedded metal nanostructures. A dense monolayer of silver nanocubes was deposited on a quartz substrate using the Langmuir-Blodgett technique and subsequently coated with an ultrathin Azo-POSS layer. The reversible light-induced photoisomerization between the trans and cis states of the azobenzene-terminated branched POSS material results in significant changes in the refractive index (up to 0.17) at a wavelength of 380 nm. We observed that the pronounced and reversible change in the surrounding refractive index results in a corresponding hypsochromic plasmonic shift of 6 nm in the plasmonic band of the embedded silver nanocubes. The reversible tuning of the plasmonic modes of noble-metal nanostructures using a variable-refractive-index medium opens up the possibility of fabricating photoactive, hybrid, ultrathin coatings with robust, real-time, photoinitiated responses for prospective applications in photoactive materials that can be reversibly tuned by light illumination.

Langmuir–Blodgett thin film for chloroform detection

Calix[4]resorcinarene (C11TEA) molecules could be deposited as an LB film by the Langmuir–Blodgett (LB) technique onto suitable substrates. Surface plasmon resonance (SPR) and UV–vis spectroscopy were employed for the characterization of these LB films. A high quality and uniform Langmuir monolayer from the water surface can be transferred onto a glass or gold coated substrates with a transfer ratio of over 95%. Thickness and refractive index values of the resultant LB films were measured using surface plasmon resonance with a value of 1.04nm per layer and 1.4 respectively. For the sensing application towards chloroform, this LB film yields a fast and almost fully reversible response to chloroform in few seconds.

Electrochemistry of LB films of mixed MGDG:UQ on ITO

The electrochemical behaviour of biomimetic monolayers of monogalactosyldiacylglycerol (MGDG) incorporating ubiquinone-10 (UQ) has been investigated. MGDG is the principal component in the thylakoid membrane and UQ seems a good substitute for plastoquinone-9, involved in photosynthesis chain. The monolayers have been performed using the Langmuir and Langmuir–Blodgett (LB) techniques and the redox behaviour of the LB films, transferred at several surface pressures on a glass covered with indium–tin oxide (ITO), has been characterized by cyclic voltammetry. The cyclic voltammograms show that UQ molecules present two redox processes (I and II) at high UQ content and high surface pressures, and only one redox process (I) at low UQ content and low surface pressures. The apparent rate constants calculated for processes I and II indicate a different kinetic control for the reduction and the oxidation of UQ/UQH2 redox couple, being kRapp(I)=2.2·10−5s−1, kRapp(II)=5.1·10−14 kOapp(I)=3.3·10−3s−1 and kOapp(II)=6.1·10−6s−1, respectively. The correlation of the redox response with the physical states of the LB films allows determining the positions of the UQ molecules in the biomimetic monolayer, which change with the surface pressure and the UQ content. These positions are known as diving and swimming.

Biomimetic collagen I and IV double layer Langmuir–Schaefer films as microenvironment for human pluripotent stem cell derived retinal pigment epithelial cells

The environmental cues received by the cells from synthetic substrates in vitro are very different from those they receive in vivo. In this study, we applied the Langmuir–Schaefer (LS) deposition, a variant of Langmuir–Blodgett technique, to fabricate a biomimetic microenvironment mimicking the structure and organization of native Bruch's membrane for the production of the functional human embryonic stem cell derived retinal pigment epithelial (hESC-RPE) cells. Surface pressure-area isotherms were measured simultaneously with Brewster angle microscopy to investigate the self-assembly of human collagens type I and IV on air-subphase interface. Furthermore, the structure of the prepared collagen LS films was characterized with scanning electron microscopy, atomic force microscopy, surface plasmon resonance measurements and immunofluorescent staining. The integrity of hESC-RPE on double layer LS films was investigated by measuring transepithelial resistance and permeability of small molecular weight substance. Maturation and functionality of hESC-RPE cells on double layer collagen LS films was further assessed by RPE-specific gene and protein expression, growth factor secretion, and phagocytic activity. Here, we demonstrated that the prepared collagen LS films have layered structure with oriented fibers corresponding to architecture of the uppermost layers of Bruch's membrane and result in increased barrier properties and functionality of hESC-RPE cells as compared to the commonly used dip-coated controls.

Fabrication of ultrathin films containing the metal organic framework Fe-MIL-88B-NH 2 by the Langmuir–Blodgett technique

Abstract In this work, the fabrication of ultrathin films containing the metal organic framework (MOF) Fe-MIL-88B-NH 2 by the Langmuir–Blodgett (LB) technique has been explored. MOF crystals of two different sizes (1.5 ± 0.3 and 0.07 ± 0.01 μm) have been synthesized and assembled at the air–liquid interface by the LB method. The effect of the subphase pH and particle size on the film formation process has been studied. Moreover, for the first time, mixed MOF + polymer (the commercial soluble polyimide Matrimid ® ) LB films containing different MOF loadings have been fabricated. These experiments show that it is possible to obtain ultrathin MOF + polymer films with a controlled MOF density. Furthermore, MOF particles are homogeneously distributed in the polymer matrix, even with very large amounts of MOF (up to 95 wt%). LB films have been incorporated into materials of different nature, including glass and mica substrates and also polymeric membranes based on polysulfone Udel ® and PIM-1 (polymer of intrinsic microporosity), and the modification of water contact angle after LB film deposition has been analyzed.

Ultra-high ordered, centimeter scale preparation of microsphere Langmuir films

Controlling the preparation of nano/microsphere monolayers on large areas remains a difficult task but is crucial for several fabrication methods of highly-ordered periodic nanostructures. We demonstrate the preparation of ordered monolayers of few square centimeters with an extremely high coverage ratio (>98%) by implementing a modified protocol (MP) Langmuir Blodgett (LB) technique. We use octadecyl type hydrocarbon (C18) functionalized spherical particles (polystyrene and silica) with diameters in the range 1–5μm, and a selected mixture of solvents for accurate control of the surface tension and particles’ mobility at the water surface. This leads to a delicate growth of crystal-like monolayers which are subsequently transferred to glass or silicon substrates. While operating the Langmuir–Blodgett trough, a key enabling the quality enhancement resides not only on surface tension measurements but also on simple visual inspections of the water surface supporting the monolayer. The protocol yields a strong reduction of sensitivity to thermodynamical and mechanical disturbances leading to a robust method that could be automated by adding a feedback on the operated system based real-time image processing. A simple analytical approach is used to explain why this MP-LB technique is more appropriate in growing micrometric-sized objects in comparison to standard protocols optimized for the preparation of molecular films.

Effect of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and phospholipase A2 (PLA2) on surface properties of silica materials

Abstract The effect of phospholipid DPPC monolayer on surface properties of powdered quartz (SiO 2 /DPPC ML ) and silicon wafer (Si/DPPC ML ) before and after phospholipase A 2 (PLA 2 ) action was determined. DPPC on quartz particles was deposited from chloroform solution and the monolayer on silicon surface by using the Langmuir–Blodgett technique. The surface free energy and its components of powdered quartz before and after contact with PLA 2 in NaCl solution were determined by imbibition–drainage method (I–DM), which is based on the capillary rise method. The probe liquids (water, formamide and diiodomethane) wick the powder bed. The DPPC monolayer supported on silicon after the contact with NaCl or Tris solution (without and with enzyme PLA 2 ) was monitored by contact angle measurements of the probe liquids. In order to visualize the changes in the DPPC monolayer structure, its topography images were obtained from AFM. The obtained results show that most evident changes in wettability, i.e. the apparent surface free energy of DPPC monolayer supported on silicon (Si/DPPC ML ) and treated with PLA 2 occur within the first 15 min after initiation of the hydrolysis. The analysis of the topography images of the phospholipid monolayer clearly reveals that degradation of monolayer occurs. The modification of quartz powder with DPPC resulted in decreased apparent surface free energy, which however increased after the PLA 2 action, up to the value obtained for bare quartz surface. This again revealed the hydrolysis reaction. The influence of PLA 2 on the surface free energy changes of DPPC monolayer deposited on silicon correlated with those observed for quartz powder. These results pointed out a complete hydrolysis of DPPC by PLA 2 enzyme. The AFM images shed more light on the relation between DPPC monolayer topography and the apparent surface free energy changes taking place during the hydrolysis catalyzed by PLA 2 .

Dendrimers complexed with HIV-1 peptides interact with liposomes and lipid monolayers

AimsWe have investigated the effect of surface charge of model lipid membranes on their interactions with dendriplexes formed by HIV-derived peptides and 2 types of positively charged carbosilane dendrimers (CBD). MethodsInteraction of dendriplexes with lipid membranes was measured by fluorescence anisotropy, dynamic light scattering and Langmuir–Blodgett techniques. The morphology of the complexes was examined by transmission electron microscopy. ResultsAll dendriplexes independent of the type of peptide interacted with model lipid membranes. Negatively charged vesicles composed of a mixture of DMPC/DPPG interacted more strongly, and it was accompanied by an increase in anisotropy of the fluorescent probe localized in polar domain of lipid bilayers. There was also an increase in surface pressure of the lipid monolayers. Mixing negatively charged liposomes with dendriplexes increased liposome size and made their surface charges more positive. ConclusionsHIV-peptide/dendrimer complexes interact with model lipid membranes depending on their surface charge. Carbosilane dendrimers can be useful as non-viral carriers for delivering HIV-peptides into cells.

Partially induced transition from horizontal to vertical orientation of helical peptides at the air–water interface and the structure of their monolayers transferred on the solid substrates

To apply the Langmuir–Blodgett (LB) technique as a platform for investigating the fundamental properties of amphiphilic peptides (APs), we have investigated the structure of LB films using the APs. To vertically orient the helical APs like transmembrane proteins in the membrane, the primary structure of the APs was designed to have two domains: a hydrophilic domain (three amino acids) and a hydrophobic domain (ca. 20 amino acids). However, we are still far from having full control of their orientation. This study reports the contribution of the subphase temperature to the change in the orientation of helical APs. When the surface pressure–area isotherm of AP was observed at the subphase temperature at 41.5°C, the isotherm exhibited a plateau, implying that a phase transition of the monolayer at the air–water interface occurred. Circular dichroism (CD) spectra of the monolayers transferred on the solid substrates revealed that the orientation of the helices changed at the pressure, where the plateau of the isotherm was observed. This change was not observed at 21.5°C, i.e., the horizontal alignment of helixes was maintained. Atomic force microscopy (AFM) was used to systematically investigate the surface structure of the monolayers transferred at different surface pressures. A structural model of the monolayer that did not contradict with the results obtained by the three different techniques (the isotherm, CD spectroscopy, and AFM) was derived, and it was concluded that the horizontally oriented helices partially changed their orientation to vertical upon compression in the plateau region of the isotherm.

On the antibacterial mechanism of graphene oxide (GO) Langmuir-Blodgett films.

The Langmuir-Blodgett (LB) technique was used to immobilize flat graphene oxide (GO) sheets on a PET substrate to ascertain as to whether the edges of GO play an integral part in its antimicrobial mechanism. The observed antibacterial activity suggests that contact with the edges is not a fundamental part of the mechanism.

Photomagnetic molecular and extended network Langmuir–Blodgett films based on cyanide bridged molybdenum–copper complexes

The present manuscript describes two types of cyanide bridged molybdenum–copper photomagnetic films obtained by the Langmuir–Blodgett technique.

Highly flexible transparent conductive graphene/single-walled carbon nanotube nanocomposite films produced by Langmuir–Blodgett assembly

Transparent conductive films composed of ultra-large graphene oxide and functionalized single-walled carbon nanotubes are assembled on a flexible poly(ethylene terephthalate) (PET) substrate using the Langmuir–Blodgett technique.

INFRARED PHOTOLUMINESCENCE SPECTRA OF PBS NANOPARTICLES PREPARED BY LANGMUIR–BLODGETT AND LASER ABLATION METHODS

We optimized the optical setup originally designed for the photoluminescence measurements in the spectral range 400‒1100 nm. New design extends the spectral range into the near infrared region 900‒1700 nm and allows the colloidal solutions measurements in cuvettes as well as the measurements of nanoparticles deposited in the form of thin films on glass substrates. The infrared photoluminescence spectra of the PbS nanoparticles prepared by the Langmuir–Blodgett technique show the higher photoluminescence intensity and the shift to the shorter wavelengths compared to the infrared photoluminescence spectra of the PbS nanoparticles prepared by the laser ablation from PbS target. We aslo proved the high stability of PbS nanoparticles prepared in the form of thin layers.

Molecularly imprinted hydrogels from colloidal crystals for the detection of progesterone

The synthesis of new nanoporous materials based on molecularly imprinted polymers (MIPs) is investigated. The novel procedure combines the non-covalent imprinting method with the colloidal crystal template technique to produce membranes with pre-specified morphology capable of selectively recognizing progesterone. The colloidal crystals made of silica particles were obtained by Langmuir − Blodgett and self-assembly techniques, and exhibited a considerable control of the film thickness. Hydrogel films were prepared by copolymerization of acrylic acid and ethylene glycol dimethacrylate in the presence of 2,2′-azobisisobutyronitrile as initiator. The polymerization took place in the interspaces of the colloidal crystal and after the reaction was finished the silica particles were etched with hydrofluoric acid to produce a 3D ordered structure. The nanocavities derived from progesterone were distributed within the walls of the internal structure of the films. The equilibrium swelling properties of the MIPs were studied as a function of crosslinking degree and pH. The pore morphology of the film was analyzed by SEM. The MIP characterizations were accomplished by several techniques, e.g. Fourier transform infrared spectroscopy, DSC and evaluation of their sensing and selective properties. © 2014 Society of Chemical Industry

Dynamic Template for Assembling Nanoparticles into Highly Ordered Two-Dimensional Arrays of Different Structures

The proper assembly of nanoparticles can enhance their properties and improve their applicability. Likewise, imprudent assembly can damage the unique properties of the nanomaterials. Accordingly, finding robust techniques for making ordered assemblies of nanoparticles is a hot topic in materials science research. In this work, the Langmuir–Blodgett (LB) technique was used to assemble polyethylene glycol (PEG)-functionalized gold nanocubes (AuNCs) into highly packed two-dimensional (2D) arrays with different structures. This technique is based on creating polymeric micelles within the AuNC monolayer, which drives the nanocubes to assemble into a highly packed structure even at low LB surface pressures. Interestingly, the micelles could be made more diffuse by changing the LB trough surface pressure, which allowed for tuning the width and the structure of the AuNC 2D arrays. The areas occupied by the micelles appeared as voids that separated the AuNC arrays and prevented the formation of a uniform monolayer of AuNCs. The polymer micelles were therefore able to act as dynamic soft templates, and the separation distances between individual nanocubes as well as the 2D array structure were controlled by changing the chain length of the PEG functionalization on the surface of the nanocubes. Theoretical calculations of the attractive and repulsive forces and the balance between them presented a good prediction for the optimum separation distance between the AuNCs inside the 2D arrays.

Temperature and concentration dependence of J-aggregate of a cyanine dye in a Laponite film fabricated by Langmuir–Blodgett technique

In this communication, we report the temperature and concentration dependence of J-aggregate of a cyanine dye N,N′-dioctadecylthiacyanine perchlorate (NK) in the Laponite film fabricated by Langmuir–Blodgett technique. Surface pressure area per molecule isotherm revealed the formation of stable Langmuir monolayer at the air–water interface. Spectroscopic characterization confirmed the formation of J-aggregates in the NK LB film without Laponite. In the hybrid film, J-aggregate forms at lower Laponite concentration (1ppm), higher deposited surface pressure and at lower subphase temperature. Both the J-aggregated films were found to be optical second harmonic generation (SHG) active and mechanically very stable, although intrinsically NK is SHG inactive.

Assembly of polystyrene-coated gold nanoparticles at the air–water interface

Gold nanoparticles (NPs) coated with thiol-terminated polystyrene chains of varying molar mass were added to polystyrene-b-polymethylmethacrylate (PS-b-PMMA) block copolymer monolayers at the air–water interface. Composite films were transferred to solid substrates by the Langmuir–Blodgett technique. For most of the investigated systems, TEM micrographs and AFM images reveal the formation of 2D island-like aggregates of particles organized on a close-packed hexagonal lattice. This characteristic aggregate formation is lost when PS ligands are within the same length regime as the PS block from the copolymer. The results are compared with those obtained for analogous systems containing no copolymer where NPs are deposited on either a bare water surface or bare glass. Interparticle distance between NPs is found to depend on the surface on which they are deposited, the presence or not of the copolymer monolayer, and ligand length.

Controlling the Catalytic Efficiency on the Surface of Hollow Gold Nanoparticles by Introducing an Inner Thin Layer of Platinum or Palladium

The efficiency of heterogeneous catalysis of electron-transfer reactions on the surface of gold nanoshells was changed by adding an inner platinum or palladium nanoshell in the double-shell nanocatalysts. The reduction of 4-nitrothiophenol (4NTP) by borohydride was studied as a model reaction. To confirm the heterogeneous catalytic mechanism, the nanocatalysts were assembled into a monolayer on the surface of a quartz substrate using the Langmuir-Blodgett technique, and the 4NTP was allowed to bind to the surface of gold through a strong thiol bond. The stages of the reduction reaction of 4NTP on the surface of gold were successfully followed by time-resolved surface-enhanced Raman spectroscopy. Palladium was found to increase the catalytic efficiency of the gold surface due to the presence of a new Fermi level of the palladium-gold alloy, while platinum decreased its catalytic efficiency due to the electron-withdrawing effect of platinum atoms, which resulted from the difference in their electrochemical reduction potentials.

White light-emitting electrochemical cells based on the Langmuir-Blodgett technique.

Light-emitting electrochemical cells (LECs) showing a white emission have been prepared with Langmuir-Blodgett (LB) films of the metallosurfactant bis[2-(2,4-difluorophenyl)pyridine][2-(1-hexadecyl-1H-1,2,3-triazol-4-yl)pyridine]iridium(III) chloride (1), which work with an air-stable Al electrode. They were prepared by depositing a LB film of 1 on top of a layer of poly(N,N'-diphenyl-N,N'-bis(4-hexylphenyl)-[1,1'-biphenyl]-4,4'-diamine (pTPD) spin-coated on indium tin oxide (ITO). The white color of the electroluminescence of the device contrasts with the blue color of the photoluminescence of 1 in solution and within the LB films. Furthermore, the crystal structure of 1 is reported together with the preparation and characterization of the Langmuir monolayers (π-A compression isotherms and Brewster angle microscopy (BAM)) and LB films of 1 (IR, UV-vis and emission spectroscopy, X-ray photoelectron spectroscopy (XPS), specular X-ray reflectivity (SXR), and atomic force microscopy (AFM)).