Number Of Bilayers Research Articles

Layer-by-Layer Assembly of Nanosized Membrane Fractions for the Assessment of Cytochrome P450 Xenobiotic Metabolism.

Herein, we report the use of sequential layer-by-layer (LbL) assembly to design nanostructured films made of recombinant bacterial membrane fractions (MF), which overexpress cytochrome P450 (CYP) and cytochrome P450 reductase. The ability to incorporate MF in LbL multilayered films is demonstrated by an in situ quartz crystal microbalance with dissipation monitoring using poly-l-lysine or poly-l-ornithine as a polycation. Results show that MF preserve a remarkable CYP1A2 catalytic property in the adsorbed phase. Moreover, atomic force microscopy images reveal that MF mostly adopt a flattened conformation in the adsorbed phase with an extensive tendency to aggregate within the multilayered films, which is more pronounced when increasing the number of bilayers. Interestingly, this behavior seems to enhance the ability of embedded MF to remain active after repeated uses. The proposed strategy constitutes a practical alternative for the immobilization of active CYP enzymes. Besides their fundamental interest, MF-based multilayers are useful nano-objects for the creation of new biomimetic reactors for the assessment of xenobiotic metabolism.

New color from multilayer coating applied machining tools based on tungsten carbide insert

TiCN/TiNbCN multilayer systems were synthetized on silicon substrates by radio frequency (r.f.) magnetron sputtering with alternatively changing the sputtering plasma composition between pure Ti+C and Nb elements under a reactive mixture of Ar/N2. Bilayer numbers were increased from nanometric range (15 nm) to higher micrometric range (1.5 μm). The structural and chemical properties were analyzed by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), cross-sectional transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), and optical properties via color purity. The multilayer period effect on the optical properties such as color purity was studied and the color dependence as function of bilayer number with niobium (Nb) modulation in the TiCN/TiNbCN system determined. The spectra for all layers showed high reflectance at large wavelengths, e.g., 92% for the TiNbCN layer, 89% for the TiCN layer, and about 75% for the TiCN/TiNbCN multilayer deposited with n = 200 and Λ = 15 nm. So the changes in the color purity present novel color applied on machining tools (tungsten carbide insert) in relation to (Nb) fluctuation which can be applied in optical and industrial applications.

Layer by Layer Mesoporous Silica-Hyaluronic Acid-Cyclodextrin Bifunctional "Lamination": Study of the Application of Fluorescent Probe and Host⁻Guest Interactions in the Drug Delivery Field.

The layer-by-layer technique was exploited to adjust the magnitude of the host–guest interactions between adamantane and cyclodextrin. The effect depends on numerous complex and changeable growth profiles of the films and the number of bilayers. These composite films of mesoporous silica nanoparticles and hyaluronic acid–cyclodextrin(HA-CD) were constructed to load the fluorescent dyes and peptides. The release rates of these molecules would decrease with an increase in the number of layers. A laser scanning confocal microscope was utilized to obtain the diffusion coefficient of fluorescein isothiocyanate. Hybrid films could be applied to increase the loading of different kinds of molecules and could also be integrated into the lamination to delay the rate of release.

Optical properties of one dimensional metal-air graded system

Using the scattering matrix formalism, in this work it is presented the numerical study of the optical properties of 1D photonic graded systems, constructed by multiple bi-layers of Drude-type metal and air, where the total amount of material, as well as the length proportion of them in each bi-layer are kept constant. A graded variation of the bi-layers length, following an arithmetic progression defined in terms of a variable δ is considered. It is shown the formation of a transmission band that grows with the number of bi-layers and how the increase of the metallic plasma frequency or the size of the system modifies the transmission spectra, resembling the response of different photonic crystals. For the transverse electric (TE) and magnetic (TM) modes, it is presented the redistribution of the transmission peaks to higher frequencies as a function of the incident angle and δ. For TM mode, it is observed the appearance of maximum transmission peaks below the metallic plasma frequency, in an equal number as the air layers of the system, whose widths decrease with the augment of the incident angle. It is observed the variation of the transmission peaks with the increase of δ, which are shifted to higher frequencies, due to the material distribution which is mainly located on one side of the system. Additionally an analytical approach for graded structures is developed.

Surface modification of anion exchange membrane using layer-by-layer polyelectrolytes deposition facilitating monovalent organic acid transport

Surface modification of commercial anion exchange membrane (AEM) to improve permselectivity for mono carboxylate anions was achieved through layer-by-layer deposition of polyelectrolytes of different polarities (poly (sodium 4-styrene sulfonate), PSS and poly (ethyleneimine), PEI). Improvement in adherence of polyelectrolytes layers was achieved by cross linking with glutaraldehyde, GA. Impact of the number of bi-layers on selective transport was investigated with 2, 5 and 10 bi-layers coatings over commercial AEM. Surface morphology (FESEM), functional groups (FTIR), hydrophilicity/hydrophobicity (contact angle), physico-chemical (ion exchange capacity and water uptake) and electrochemical (permselectivity and membrane resistance) properties were characterized with modified (2, 5 and 10 bi-layers) and unmodified AEMs. Contact angle lowering with increase in number of coated bi-layers confirmed rise in hydrophilicity of the modified AEM surface. 10 bi-layer coated AEM showed 4 times improvement (relative to unmodified AEM) in permselectivity with acetate (AA−) ions during batch electrodialysis (ED) of ternary acid mixture (acetic, malic and citric). Energy consumptions per kg of acetic acid recovery with modified (M10) and unmodified AEMs were 0.66 kW h and 0.56 kW h respectively indicating rise in resistance with coating. Permselectivity values of modified membrane (bi-ionic potential) confirmed the observed trend in ED recovery (acetate, AA− > malate, MA2− > citrate, CA3−).

Reflectance and color purity obtained for novel Ti[sbnd]C[sbnd]N/Ti[sbnd]Nb[sbnd]C[sbnd]N multilayers as function of niobium (Nb) modulation

Carbon-nitride multilayer systems were synthetized on silicon substrates by r.f. magnetron sputtering with alternatively changing the sputtering plasma composition between pure Ti+C and Nb elements under a reactive mixture of Ar/N2. Bilayer numbers were increased from nanometric range (15 nm) to higher micrometric range (1.5 μm). The structural and chemical properties were analyzed by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), cross-sectional transmission electron microscopy (TEM), Electron energy loss spectroscopy (EELS) and optical properties via color purity. The multilayer period effect on the optical properties such as color purity was studied and the color dependence as function of bilayer number with niobium (Nb) modulation in the TiCN/TiNbCN system determined. The spectra for all layers showed high reflectances at large wavelengths, e.g. 92% for the TiNbCN layer, 89% for the TiCN layer and about 75% for the TiCN/TiNbCN multilayer deposited with n = 200, Λ = 15 nm, So the changes in the color purity in relation to (Nb) fluctuation can be applied in optical and industrial applications.

Layer-by-layer assembled graphene oxide/polydiallydimethylammonium chloride composites for hydrogen gas barrier application

Poly(diallyldimethylammoium chloride) (PDDA)/acid or base modified graphene oxide (MGO) composite (PDDA/MGO)-based gas barrier films were prepared by layer-by-layer (LBL) assembly method on polyethylene terephthalate (PET) substrate using a spray coating assisted deposition. The effect of pH on the hydrogen gas permeability (H2GP) values of the different MGO-based films was investigated to determine the optimum pH value of the MGO solution for the preparation of PDDA/MGO-based LBL assembly. Accordingly, the different numbers of bilayers based LBL-assembled films were prepared using alternate deposition of PDDA and MGO solutions and the H2GP values were measured for those assemblies. The films were characterized by XRD, FT-IR, and Raman spectroscopy analyses. The morphology of the LBL-assembled film was observed by cross-sectional field emission scanning electron microscopy which confirms densely packed layered structure. The H2GP of six bilayers PDDA/MGO composite film is 5.7 cc/m2⋅d⋅atm, which is much lower than that of pure PET substrate (170.7 cc/m2⋅d⋅atm), indicating 96.7% decrease in H2GP. This result suggests that the PDDA/MGO composite film could be used as a potential candidate to fabricate hydrogen gas barrier coating material.

The Fabrication of rGO/(PLL/PASP)3 @DOX Nanorods with pH-Switch for Photothermal Therapy and Chemotherapy.

The development of well-controlled drug carriers that are stable and highly effective for the delivery of anticancer agents is challenging. Herein, we report a novel pH-controlled drug delivery system, utilizing reducing graphene oxide (rGO)-polymer self-assembly films as carriers, for the preparation of effective drug nanorods and nanoparticles. In this system, the rGO-polymer carriers were constructed by the alternating assembly of poly-l-lysine (PLL) and polyaspartic acid (PASP) around the rGO sheets. Furthermore, the rGO-polymer cores, which possess a positively charged surface as the desired template, could assemble with negatively charged doxorubicin (DOX) via electrostatic interactions. The DOX embedding efficiency and the morphology of the drug nanocomposites could be controlled by the number of rGO-polymer bilayers and concentration of the rGO-polymer bilayers and the initial DOX concentration. Importantly, the release of DOX could be regulated by controlling the pH and by using a NIR laser. Under acidic conditions, the interactions between the PASP layer and DOX molecules can be broken, resulting in gradual release of the DOX molecules. Upon NIR irradiation, the release of DOX could be further accelerated and a photothermal effect from rGO induced. Cellular uptake and cytotoxicity experiments indicate that the drug nanocomposites possess effective anticancer activity. Thus, in this work, we present a useful strategy for the fabrication of pH-responsive drug nanocomposites for combined photothermal and chemical therapy. The nanocomposite can be used as a potential drug delivery system for practical cancer treatment.

Resistive switching control for conductive Si-nanocrystals embedded in Si/SiO2 multilayers

In this paper, we report on the enhanced control of resistive switching in multilayer Si/SiO2 structures, which permit the formation of Si nanocrystals with a typical size of 5.88 nm and overall good shape homogeneity. The deposition of a different number of Si and SiO2 bilayers (6, 8 and 10) allowed control of SET/RESET voltages in negative bias ranges 4.5–10 V and 6.3–13 V for six- and ten-bilayer devices, respectively. The corresponding resistance ratio between ON/OFF states varied in the ranges 107–105 for the aforementioned number of bilayers. Based on the result of XPS measurements, we suggest that the resistive switching in the studied system occurs due to the formation and annihilation of Si−Si and Si−O bonds, which serve as conductive pathways and isolating material, respectively.

Performance comparison of macromolecular assisted and immobilized low pressure membranes in the removal of toxic metals

The removal of toxic heavy metals (Cd, Pb and Hg) from aqueous solution has been attempted in two different modes by using macromolecular assisted and immobilized multilayered modified polyether sulfone membranes (PES). PES membrane was modified with chitosan (CHI) and poly (styrene sulfonate) (PSS) using layer by layer (LbL) method. Humic acid (HA) and cholesterol (CHO) were used for immobilization. SEM and AFM confirmed that the obtained films were rough and highly porous. FTIR analysis confirmed successful immobilization of macromolecules in poly-ion coated membranes. Ellipsometric studies confirmed that the thickness of system increased with immobilization. Thermogravimetric analysis proved that the membranes were thermally stable upto 550 °C. The macromolecule assisted low pressure filtration was carried out by the addition of HA and CHO to the respective spiked metal ion solutions prior to filtration. More than 98% of the heavy metal ions were retained by macromolecules immobilized membranes. For Cd2+ ions, rejection efficiency of 6 bilayered PES membrane achieved ∼90% with HA and CHO immobilized at a concentration of 20 μmol/L and 400 μmol/L respectively. For Pb2+ ions, rejection efficiency attained ∼90% for HA (2 bilayered system) and for CHO (4 bilayered system) immobilized at 15 μmol/L and 400 μmol/L respectively. The rejection efficiency for Hg2+ ions obtained above 95% for both HA and CHO immobilized membranes at 2 bilayer with concentrations 15 μmol/L and 300 μmol/L respectively. The macromolecule assisted filtration also showed very good removal for all metal ions with efficiency above ∼90%. High macromolecule concentration with high number of bilayers has resulted high flux with negligible effect on the retention of heavy metals. Thus, this membrane system provides a very simple, efficient, easy and convenient approach for the removal of toxic metal ions by employing a combination of poly-ion coated polymer membrane with macromolecules.

AFM study of adhesion and interactions between polyelectrolyte bilayers assembly

In this report we present the influence of the first polyelectrolyte layer and the number of subsequent bilayers on physicochemical interactions and adhesion forces in polyelectrolyte multilayers (PEM) composed of poly(ethyleneimine) (PEI) and poly(styrene sulfonate) (PSS) deposited by layer-by-layer (LbL) technique on gold substrate. Morphology, thickness and adhesive properties of polyelectrolyte multilayers were studied by the means of AFM imaging and force spectroscopy methods, in relation to the number of deposited layers and polyelectrolyte deposition order. Thickness growth was quicker for PEI/PSS comparing to PSS/PEI sequence bilayers. Thickness values varied from 4.9 nm to 25.4 nm. The adhesion measurements demonstrate that interaction forces between the probe and PEM varied from 1 nN to 20 nN and increased with time of probe-sample contact. Attractive interactions were observed for systems capped with either PEI or PSS. For PEI capped films multiple snap-off points were observed suggesting a creation of bridge-like structures between the deposited film and sensing probe. PSS capped films showed no such features. It is proposed that PSS is adsorbed on Au by its hydrophobic carbon chain, while hydrophilic sulfonate groups are oriented towards bulk solution when PEI is adsorbed on Au surface via attractive electrostatic interactions between positively charged nitrogen atoms and a negatively charged gold surface.

A Green Method to Fabricate Polyethyleneimine-Alginate Multilayer Coatings Modified Polyurethane Foam for Cu2+ Adsorption from Aqueous Solution

ABSTRACTIn this study, flexible polyurethane foam (FPUF) was modified with bio-based coatings composed of polyethylenimine (PEI) and alginate (ALG), fabricated by layer-by-layer (LbL) self-assembly. LbL self-assembled coatings modified FPUFs were studied for their potentials for removing Cu2+ ions from aqueous solutions by using batch adsorption technique, as a function of assembled bilayers number, pH value, carrier amount and adsorption time. The maximum adsorption capacity of the modified FPUF was shown to be 54 mg/g for Cu2+. Results suggested that the LbL self-assembly could potentially be a promising cost-effective technique for fabricating advanced adsorbent materials for removing pollutants from wastewater.

Fabrication of Bifunctional TiO2/POM Microspheres Using a Layer-by-Layer Method and Photocatalytic Activity for Methyl Orange Degradation

Bifunctional films of Keggin-type polyoxometalates H3PW12O40 (PW12), H4SiW12O40 (SiW12), H3PMo12O40 (PMo12), and TiO2 were successfully built on Fe3O4@SiO2 microspheres using a layer-by-layer method. The characterization by field emission scan electronic microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX) shows that TiO2 nanoparticles and polyoxometalate (POM) anions are successfully assembled. The photodegradation of methyl orange (MO) was used to test the photocatalytic efficiency of magnetic catalysts under UV irradiation. For MO decomposition, multilayer films that combine PW12 and SiW12 with TiO2 show high efficiency, which can be attributed to the synergistic effect between POMs and TiO2. The degradation of the model contaminant was also systematically checked under different conditions such as bilayer number deposited on magnetic microspheres, catalyst concentration, inorganic oxidants, and salts. The oxidation process of MO follows an apparent first-order reaction. Furthermore, the composite catalysts deposited on Fe3O4@SiO2 magnetic microspheres can be conveniently, quickly, and efficiently separated by an external magnet from a solution.

Poly(allylamine hydrochloride) (PAH) and Bovine Serum Albumin (BSA) Protein Nanostructured as Layer-by-Layer Thin Films.

In this work it was studied the production of nanostructured thin films containing alternating layers of poly(allylamine hydrochloride) (PAH) and bovine serum albumin protein (BSA). It was studied the adsorption processes of these materials onto solid surfaces, which included adsorption kinetics and film growth studies by using UV-Vis spectroscopy. The film morphology, thickness and roughness were studied by using atomic force microscopy (AFM). The AFM results showed that the film presented a globular-like surface morphology and a thickness within the nanoscale, which could be controlled by the number of deposited layers. The roughness and thickness of the film depend on the number of deposited bilayers, where the film roughness increased for films with a number of bilayers up to five, after which the film roughness remained almost constant. This is an indicative that the adsorption and growth processes might occur under two different mechanisms, first under the influence of the substrate (films containing up to five bilayers of PAH/BSA), and second under the influence of the film previously deposited (films containing more than five bilayers of PAH/BSA), respectively.

Insulating chitosan/casein multilayers on corona charged polylactic acid substrates

The influence of the structure and physico-chemical properties of chitosan/casein multilayer films on their potential use for drug delivery systems was investigated. The multilayer films were prepared using layer-by-layer self-assembly, whereby chitosan and casein were deposited onto poly(lactic acid) substrates pretreated with either a positive or a negative corona. The corona discharge system consisted of a corona electrode, a grounded plate and a grid. The deposition was studied by ATR FT-IR, AFM, and surface energy measurements. ATR FT-IR spectra proved the formation of polyelectrolyte chitosan — casein complexes. The increasing content of chitosan and casein with increasing number of bilayers was further confirmed by XPS analysis. The surface topography was examined by AFM and the average roughness was evaluated. A comparative analysis of the experimental results was performed and the most appropriate substrate corona treatment for the irreversible binding of the chitosan/casein polyelectrolytes was determined.

Thermal cyclic response of [8YSZ/Al2O3]n multilayered coatings deposited onto AISI 304 stainless steel

8%Yttria-Stabilized Zirconia (8YSZ) and Alumina (Al2O3) coatings were deposited on silicon (100) and stainless steel AISI 304 substrates as single layers and [8YSZ/Al2O3]n multilayer, via a multi-target r.f. (13.56 MHz) magnetron sputtering system, from 8mol% Y2O3-ZrO2 and aluminum (99.95%) targets under an Ar/O2 atmosphere at 300 °C. The effect of the Al2O3/8YSZ bilayers number (n = 1, 10, 30, 50 and 70) on the thermal cyclic response was studied. For this test, the coatings were heated and cooled in air flux during 12 h by cycles of 10 min at 1000 °C. After this process, the oxide scale at the surface of the coatings was studied by digital image analysis, X-ray diffraction, Scanning Electron Microscopy, and Energy Dispersive X-Ray Spectroscopy. It was found a phase transformation from tetragonal to monoclinic ZrO2, deriving in a volume expansion, which caused the coatings cracks formation. Also, a reduction of superficial degradation from 80.6% (for n = 1 bilayer) to 0.3% (for n = 70 bilayers) was observed. Moreover, it was evidenced that the iron oxides formed at the uncoated substrates, decreased by the increment of bilayers number. The intensity of high-temperature oxidation of [8YSZ/Al2O3]n coatings decreased with increasing the number of bilayers, which shows that O2 ions diffusion, through defects or vacancies in the lattice structure, has been limited.

Development and Characterization of New Pervaporation PVA Membranes for the Dehydration Using Bulk and Surface Modifications.

In the present work, the novel dense and supported membranes based on polyvinyl alcohol (PVA) with improved transport properties were developed by bulk and surface modifications. Bulk modification included the blending of PVA with chitosan (CS) and the creation of a mixed-matrix membrane by introduction of fullerenol. This significantly altered the internal structure of PVA membrane, which led to an increase in permeability with high selectivity to water. Surface modification of the developed modified dense membranes, based on composites PVA-CS and PVA-fullerenol-CS, was performed through (i) making of a supported membrane with a thin selective composite layer and (ii) applying of the layer-by-layer assembly (LbL) method for coating of nano-sized polyelectrolyte (PEL) layers to increase the membrane productivity. The nature of polyelectrolyte type—(poly(allylamine hydrochloride) (PAH), poly(sodium 4-styrenesulfonate) (PSS), poly(acrylic acid) (PAA), CS), and number of PEL bilayers (2–10)—were studied. The structure of the composite membranes was investigated by FTIR, X-ray diffraction, and SEM. Transport properties were studied during the pervaporation separation of 80% isopropanol–20% water mixture. It was shown that supported membrane consisting of hybrid layer of PVA-fullerenol (5%)–chitosan (20%) with five polyelectrolyte bilayers (PSS, CS) deposited on it had the best transport properties.

Fire protection behavior of layer-by-layer assembled starch–clay multilayers on cotton fabric

UV–Vis spectrometry and quartz crystal microbalance were used to measure the growth of these films as a function of the number of bilayers deposited, while scanning electron microscopy and transmission electron microscopy were used to visualize the morphology of the thin film coatings on the cotton fabric. Nanocomposites formed of cationic starch (CS) and clay introduced fire protection properties into the pure cotton fabric by layer-by-layer (LbL) technique. The optical properties and mass of the films were precisely controlled by the number of bilayers. In this case, CS and clay multilayer thin films were used to increase the thermal stability of the fabrics and improve the anti-flammable properties through the formation of a ceramic char layer and thermally stable carbonaceous structure at a high temperature. This study demonstrates the ability of the LbL technique to produce anti-flammable starch–clay nanocomposite thin films. Cone calorimetry showed the lower total heat release and heat release capacity of the LbL-coated fabric. The LbL-coated cotton samples exhibited a reduced afterglow time in vertical flame tests. An increased amount of residue indicates that the LbL technique is a simple method which can be used to produce eco-friendly flame retardant thin film coatings.

Photophysical study of the interaction between ZnO nanoparticles and globular protein bovine serum albumin in solution and in a layer-by-layer self-assembled film

In this study, we investigated the spectroscopic properties of the water-soluble globular protein bovine serum albumin (BSA) while interacting with zinc oxide (ZnO) semiconductor nanoparticles (NPs) in aqueous medium and in a ZnO/BSA layer-by-layer (LbL) self-assembled film fabricated on poly (acrylic acid) (PAA)-coated quartz or a Si substrate via electrostatic interactions. BSA formed a ground state complex due to its interaction with ZnO NPs, which was confirmed by ultraviolet–visible absorption, and steady state and time-resolved fluorescence emission spectroscopic techniques. However, due to its interaction with ZnO, the photophysical properties of BSA depend significantly on the concentration of ZnO NPs in the mixed solution. The quenching of the fluorescence intensity of BSA in the presence of ZnO NPs was due to the interaction between ZnO and BSA, and the formation of their stable ground state complex, as well as energy transfer from the excited BSA to ZnO NPs in the complex nano-bioconjugated species. Multilayer growth of the ZnO/BSA LbL self-assembled film on the quartz substrate was confirmed by monitoring the characteristic absorption band of BSA (280 nm), where the nature of the film growth depends on the number of bilayers deposited on the quartz substrate. BSA formed a well-ordered molecular network-type morphology due to its adsorption onto the surface of the ZnO nanostructure in the backbone of the PAA-coated Si substrate in the LbL film according to atomic force microscopic study. The as-synthesized ZnO NPs were characterized by field emission scanning electron microscopy, X-ray powder diffraction, and dynamic light scattering techniques.

Synergistic Enhancement of Enzyme Performance and Resilience via Orthogonal Peptide–Protein Chemistry Enabled Multilayer Construction

Protein immobilization is critical to utilize their unique functions in diverse applications. Herein, we report that orthogonal peptide-protein chemistry enabled multilayer construction can facilitate the incorporation of various folded structural domains, including calmodulin in different states, affibody, and dihydrofolate reductase (DHFR). An extended conformation is found to be the most advantageous for steady film growth. The resulting protein thin films exhibit sensitive and selective responsive behaviors to biosignals, such as Ca2+, trifluoperazine, and nicotinamide adenine dinucleotide phosphate (NADPH), and fully maintain the catalytic activity of DHFR. The approach is applicable to different substrates such as hydrophobic gold and hydrophilic silica microparticles. The DHFR enzyme can be immobilized onto silica microparticles with tunable amounts. The multilayer setup exhibits a synergistic enhancement of DHFR activity with increasing numbers of bilayers and also makes the embedded DHFR more resilient to lyophilization. Therefore, this is a convenient and versatile method for protein immobilization with potential benefits of synergistic enhancement in enzyme performance and resilience.