Self-assembled Multilayers Research Articles

Fiber optic SPR sensor for human Immunoglobulin G measurement based on the MMF-NCF-MMF structure

Abstract A sensitive, simple fiber optic surface plasmon resonance (SPR) sensor based on the MMF-NCF-MMF structure is proposed in this work. The structure of the sensing part is constructed by a section of noncore fiber (NCF) sandwiched between two multimode fibers (MMF). Gold film with a thickness of 50 nm was uniformly sputtered on the outside surface of the NCF. SPR phenomenon was stimulated and experimentally verified when light propagates at the interface between the dielectric and the gold layers. The length of the NCF section was optimized by experiments and determined to be 12 mm. The refractive index (RI) sensitivity of the SPR sensor is 3475.1 nm/RIU in the RI range of 1.343–1.373. For the realization of human Immunoglobulin G detection, the surface of this SPR sensor needs to be biomodified. A simple process of polyelectrolyte self-assembled multilayers (PSAMs) deposition cycled four times utilizing diallyldimethyl ammonium chloride (PDDA) and styrenesulfonate sodium salt (PSS). And we choose goat anti-human immunoglobulin G-human immunoglobulin G as a bioconjugated pair to examine the bio-sensing effectiveness of this SPR sensor, the maximum sensitivity of Immunoglobulin G (IgG) detection and the limit of detection (LOD) is calculated to be 57.06 nm/(mg/ml) and 1.75 μg/ml, respectively. The proposed sensor is simple, easy to fabricate, low loss, cost-effective and can be used in numerous chemical and biological analyses.

Identification of Histophilus somni by a nanomaterial optical fiber biosensor assay.

Histophilus somni is an opportunistic pathogen responsible for respiratory and systemic diseases of cattle and sheep. Rapid and accurate detection of H. somni is essential to distinguish H. somni from other potential pathogens for proper control and treatment of infections. Nanomaterial optical fiber biosensors (NOFS) recognize analyte interactions, such as DNA hybridization, with high specificity and sensitivity, and were applied to detect H. somni DNA in culture and clinical samples. An ionic self-assembled multilayer (ISAM) film was fabricated on a long-period grating optical fiber, and a biotinylated, nucleotide probe complementary to the H. somni 16S rDNA gene was coupled to the ISAM film. Exposure of the ISAM::probe to ⩾100 killed cells of H. somni strain 2336 without DNA amplification resulted in attenuation of light transmission of ⩾9.4%. Exposure of the complexed fiber to Escherichia coli or non- H. somni species of Pasteurellaceae reduced light transmission by ⩽3.4%. Exposure of the ISAM::probe to blood, bronchoalveolar fluid, or spleen from mice or calves infected with H. somni resulted in ⩾24.3% transmission attenuation. The assay correctly detected all 6 strains of H. somni tested from culture, or tissues from 3 separate mice and calves tested in duplicate. Six heterologous strains (representing 6 genera) reacted at below the cutoff value of 4.87% attenuation of light transmission. NOFS detected at least 100 H. somni cells without DNA amplification within 45 min with high specificity. Although different fibers could vary in signal sensitivity, this did not affect the sensitivity or specificity of the assay.

Poly-l-lysine/poly-l-glutamic acid-based layer-by-layer self-assembled multilayer film for nitric oxide gas delivery

Nitric oxide (NO) gas is an endogenously produced radical gas involved in numerous physiological and pathological processes in the human body and shows potential for biomedical applications. Numerous studies have attempted to develop an NO-releasing platform in the past few decades. To take advantage of exogenous NO gas delivery, controlling the total concentration and release profile are the most important factors. To develop a controlled NO-releasing system, we used the poly-l-lysine (PLL) and poly-l-glutamic acid (PGA) because of their high biocompatibility in biomedical applications. We constructed (PLL/PGA)n multilayer thin films using the layer-by-layer self-assembly technique. We then synthesized the N-diazeniumdiolate, a proton-responsive NO donor, into the polypeptide multilayer film in a high-pressure reaction under NO gas. We investigated the film growth profile by quartz crystal microbalance and thickness measurements and determined the film surface morphology by scanning electron microscopy and atomic force microscopy. By comparing films with different thicknesses, we confirmed NO donor formation by UV–vis and Fourier-transform infrared spectroscopy. We also determined the release profiles of each film using a real-time NO analysis machine (NOA280i).

Molecular Photon Upconversion Solar Cells Using Multilayer Assemblies: Progress and Prospects.

Molecular photon upconversion via triplet-triplet annihilation (TTA-UC) is an intriguing strategy to increase solar cell efficiencies and surpass the Shockley-Quiesser (SQ) limit. In this Perspective, we recount our group's efforts to harness TTA-UC by directly incorporating metal ion linked multilayers of acceptor and sensitizer molecules into an organic-inorganic hybrid solar cell architecture. These self-assembled multilayers facilitate both upconverted emission and photocurrent generation from the upconverted state with a record contribution of 0.158 mA cm-2 under 1 sun solar flux. We recount the progression toward this record and the mechanistic insights learned along the way, summarize the rate- and efficiency-limiting events, and outline improvements that must be made to produce a viable TTA-UC solar cell that can surpass the SQ limit. We also discuss the potential impact that efficient TTA-UC and photocurrent generation could have on existing record solar cells.

Formation and Ripening of Self-Assembled Multilayers from the Vapor-Phase Deposition of Dodecanethiol on Copper Oxide

The vapor-phase reaction of dodecanethiol (DDT) with copper oxide surfaces and the molecular level composition and structure of the resulting films were examined. Atomic force microscopy, cross-sec...

CHARACTERIZATION OF OCTADECYLTRICHLOROSILANE SELF-ASSEMBLED MULTILAYERS ON PYREX GLASS

In this paper, octadecyltrichlorosilane (OTS) self-assembled multilayer (SAM) films are fabricated on Pyrex glass by dipping method. The hydrophobicity, constituent and surface morphology of OTS SAM at various dipping times in solutions of 1, 2 and 5[Formula: see text]mM concentrations are investigated. Characteristic absorption peaks around 2850 and 2920[Formula: see text]cm[Formula: see text] are observed by FTIR and island-like structures on samples are detected by AFM. After 15[Formula: see text]min dipping time for solution of 5[Formula: see text]mM, water contact angle of the sample reaches the maximum value of 116.4[Formula: see text] with relatively low surface root mean square (Rms) roughness of 0.152[Formula: see text]nm. The critical surface tension ([Formula: see text] of the analyzed sample is 18.2[Formula: see text]dyne/cm. The optimum dipping time in the solution of 5[Formula: see text]mM for a complete SAM film is about 30[Formula: see text]min. The study of the optimal conditions for the formation of integrated OTS SAM has significant scientific and practical values in modification of solid surfaces.

Use of Modified Colloids and Membranes to Remove Metal Ions from Contaminated Solutions

An efficient process was developed allowing the removal of metal ions from polycontaminated aqueous solutions by combining modified colloids and membranes. Firstly, filtration experiments were performed using polyethersulfone membranes modified by a self-assembled multilayer film of polyelectrolytes. These polymer-modified membranes allowed the uptake of more than 90% of the metal ions initially present in the contaminated solutions (for solutions concentrated at 50 mg L−1). Secondly, adsorption experiments were carried out with colloidal silica encapsulated with carboxymethyl chitosan (SiO2-CMCS) or with mesoporous silica functionalized by grafting of 1,4,8,11-tetraazacyclotetradecane, i.e., cyclam (SiO2-cyclam). The adsorption capacity of these compounds was shown to be higher than numerous other literature-known adsorbents, reaching 68 and 61 mg g−1 towards Cu(II) for SiO2-CMCS and SiO2-cyclam, respectively. Finally, by coupling adsorption with ultrafiltration in the tangential mode, the removal of Cu(II), Ni(II) and Zn(II) ions was found to be improved, allowing to reach a removal efficiency of 99% towards Cu(II), Ni(II) and Zn(II) ions at a metal concentration of 50 mg L−1, and a promising removal efficiency around 70% at a very high metal concentration of 1200 mg L−1. The mechanisms involved in the capture of the metal ions by modified membranes and colloids are also discussed.

Elucidating the Role of the Metal Linking Ion on the Excited State Dynamics of Self-Assembled Bilayers

Metal ion-linked, self-assembled multilayers on nanocrystalline metal oxide surfaces have recently emerged as an effective strategy for manipulating energy and electron transfer dynamics at organic–inorganic interfaces. The choice of metal ion can have a large impact on the stability, loading concentration, and other properties of the films. Here we report our investigation into the role of the linking ion on the subnanosecond excited state dynamics in the bilayer films (TiO2–B–M–RuP). While metal linkers like CdII, LaIII, SnIV, ZnII, and ZrIV are photochemically inert, paramagnetic linking ions such as CuII, FeII, and MnII quench the excited state of the dye with a rate constant on the order of 108 s–1. The absence of new spectral features in the transient absorption spectrum suggests that energy transfer, and not electron transfer, is responsible for the excited state quenching. On TiO2, the electron injection rate for TiO2–B–M–RuP is an order of magnitude slower (∼1 × 109 s–1) than for the dye directly...

Selective Gas Permeation in Graphene Oxide-Polymer Self-Assembled Multilayers.

The performance of polymer-based membranes for gas separation is currently limited by the Robeson limit, stating that it is impossible to have high gas permeability and high gas selectivity at the same time. We describe the production of membranes based on the ability of graphene oxide (GO) and poly(ethyleneimine) (PEI) multilayersto overcome such a limit. The PEI chains act as molecular spacers in between the GO sheets, yielding a highly reproducible, periodic multilayered structure with a constant spacing of 3.7 nm, giving a record combination of gas permeability and selectivity. The membranes feature a remarkable gas selectivity (up to 500 for He/CO2), allowing to overcome the Robeson limit. The permeability of these membranes to different gases depends exponentially on the diameter of the gas molecule, with a sieving mechanism never obtained in pure GO membranes, in which a size cutoff and a complex dependence on the chemical nature of the permeant is typically observed. The tunable permeability, the high selectivity, and the possibility to produce coatings on a wide range of polymers represent a new approach to produce gas separation membranes for large-scale applications.

Optical and Morphology Changes upon Self-Assembly of Tetrasulphonated Copper Phthalocyanine and Polyaniline Particles on Zinc Oxide Nanorods

Zinc oxide (ZnO) nanorods were grown on the pre-seeded substrate using a facile, solution route technique. The multilayer self-assembly of polyaniline (PAni) and tetrasulphonated phthalocyanine (TSCuPc) on ZnO nanorods was monitored by FTIR, UV-Vis SEM and XRD. Infrared spectrum of the assembled layer showed peaks centered at 1589cm-1and 1504 cm-1, confirmed the presence of quinoid and benzenoid structures of PAni, while peaks centered at ~1165cm-1and ~775cm-1 provided evidence for the presence of TSCuPc species. Absorption spectra of the assembled layer show broadened peaks at ~600nm and ~700nm affirmed the presence of PAni and TSCuPc molecules. A linear increase in the absorbance level at these wavelengths was also observed upon increasing the number of bilayers. The surface modification of the ZnO nanorods after self-assembly was confirmed through SEM. The edges of the ZnO nanorods was observed to change from sharp to dull upon employing layer by layer deposition of PAni and TSCuPc. XRD pattern of the assembled layer showed broadened peaks at low 2Θvalues associated to the amorphous nature of the emeraldine base of PAni. Even so, the diffraction peaks in XRD patterns of ZnO nanorods and ZnO/(TSCuPc-PAni) multilayer have been indexed as hexagonally wurtzite structure. The multilayer deposition of PAni and TSCuPc on the surface of ZnO as monitored by UV-Vis spectroscopy and confirmed by FTIR, XRD, and SEM provides a new way of anchoring dye molecules without carboxylic moieties on the surface of metal oxides

Reversible and Fast Responsive Optical Fiber Relative Humidity Sensor Based on Polyelectrolyte Self-Assembly Multilayer Film

A high-performance fiber-optic relative humidity (RH) sensor was prepared by layer-by-layer self-assembly of polycation, poly (4-vinylpyridinium chloride), and polyanion, sodium alginate, on the surface of a thin-core fiber modal interferometer. The process of layer-by-layer self-assembly was monitored by UV-vis spectroscopy and surface profilometer. The morphology of the fabricated multilayer film was characterized by atomic force microscopy and field emission scanning electron microscopy. A fast, reversible, and linear response to RH with a high resolution of 0.1 nm/1% RH has been experimentally demonstrated by the proposed fiber-optic sensor.

Fluorescence enhancement of carbon dots by graphene for highly sensitive detection of tetracycline hydrochloride.

In this study, fluorescence of self-assembled multilayers (SAMs) of carbon dots (CDs) was found to be enhanced by graphene. The number of polyelectrolyte layers can be tuned to control the distance between CDs and graphene in SAMs. The enhanced fluorescence efficiency was found to be dependent on graphene concentration, degree of graphene reduction, and the distance between CDs and graphene surface. When graphene concentration and polyelectrolyte bilayer number were set to 0.005 mg mL−1 and 3 layers, respectively, fluorescence intensity of CDs could be increased up to 3.2 times. Tetracycline hydrochloride (Tc) could be detected by the established SAMs in the presence of graphene as the sensitivity was 2 orders higher than that of SAMs in the absence of graphene. Limit of detection of this sensing system was 0.9284 nM, which is 1–3 orders of magnitude lower than those of most of reported fluorescence sensors. This method could be successfully applied to detect trace Tc in milk samples.

Enhanced fluorescence based on graphene self-assembled films and highly sensitive sensing for VB12

In this work, graphene self-assembled multilayers (SAMs) could be successfully employed to construct a surface-enhanced fluorescence (SEF) system.

G-quadruplex formation enhancing energy transfer in self-assembled multilayers and fluorescence recognize for Pb2+ ions

Here we demonstrate a novel strategy for the detection of Pb2+ ions and DNA based on the fluorescence resonance energy transfer in the self-assembled multilayers (SAMs). Quartz/GO/PDDA/G5/PDDA/GQDs@GSH SAMs were built by employing graphene oxide (GO) as the energy acceptor, glutathione-functionalized graphene quantum dots (GQDs@GSH) as the energy donor as well as poly(diallydimethylammonium) chloride (PDDA) and G5 (G-rich DNA) strand as the linker. In the presence of a certain amount of Pb2+ ions, G5 DNA could be folded into G-quadruplex, which was confirmed by Quartz Crystal Microbalance (QCM) experiments. The formation of G-quadruplex could lead to a change in the chain length and the shortening of the distance between GO and GQDs@GSH, thereby, the efficiency of energy transfer between GQDs@GSH and GO was enhanced with the quenching of fluorescence of GQDs@GSH. Meanwhile, Pb2+ ions could be recognized successfully.

Fabrication of surface-modified poly(3-aminobenzoic acid)/multiwalled carbon nanotubes composite thin films for hydrogen peroxide sensing

ABSTRACTThis work reports the fabrication of poly(3-aminobenzoic acid), (PABA)/multiwalled carbon nanotubes (MWNTs) composite thin film modified with layer-by-layer (LbL) self-assembled multilayers of cytochrome C (Cyt C) and poly(diallyldimethylammonium chloride) (PDADMAC) for hydrogen peroxide (H2O2) sensing on indium tin oxide-coated glass substrate. An electropolymerized PABA/MWNTs composite thin film was employed for the covalent attachment of Cyt C. The subsequent multilayers of PDADMAC and Cyt C were then fabricated using LbL deposition technique. The fabricated film was characterized by UV-vis spectroscopy, Raman spectroscopy, SEM and AFM. The modified thin film was finally used for successive detection of H2O2 at constant applied potential through an electrochemical method.

Development of a bioelectrode fabricated with a multilayer thin film of poly(diallyldimethylammonium)/gold-nanoparticle/lactate oxidase for analysis of l-lactate in food samples

Multilayer films made of poly(diallyldimethylammonium) (PDDA), gold nanoparticles (AuNP) of 10nm diameter and lactate oxidase (LOx), were built for the first time, by layer-by-layer (LBL) assembly technique onto both quartz and gold substrates. The surface plasmon resonance (SPR) band of AuNP was used for monitoring the film growth and adsorption kinetics on PDDA monolayer supported onto quartz substrate. In the case of polycrystalline gold surfaces, electrochemical characterization was performed by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The latter system was used as bioelectrode for l-lactate quantification, showing a short time response (<10s) with high sensitivity of 63±3μAmM−1cm−2, detection limit of 0.47μM and linear range between 0.001mM and 0.25mM. This bioelectrode was also tested for l-lactate analysis in yogurt and fermented milk, and it was checked that typical interfering as glucose and citric, acetic and ascorbic acids do not play a role. Present results indicate that self-assembled multilayers made of PDDA/AuNP/LOx are suitable thin films for electroanalytical determination of l-lactate in real samples.

Micro-Patterned Polystyrene Sheets as Templates for Interlinked 3D Polyelectrolyte Multilayer Microstructures

Polystyrene (PS) is currently mainly used as a sacrificial template during pattern release upon microcontact printing or for self-assembled flat free-standing films. We hereby present a method for creating 3D microstructured free-standing self-assembled polyelectrolyte multilayer (PEM) thin films. The approach presented utilizes a sacrificial microstructured PS template which can be coated with PEM thin films, whereby dissolution of the PS facilitates a free-standing 3D microstructured PEM film. The PS templating approach allows for omitting hot embossing on silicon masters, since PS templates can be prepared by drop casting on silicon masters. The prepared PEM film offers, if gold nanoparticles are incorporated, stimuli-responsive properties like light-induced chamber opening.

Layer-by-layer self-assembled multilayers on PEEK implants improve osseointegration in an osteoporosis rabbit model

This study aims to fabricate and deposit nanoscale multilayers on polyetheretherketone (PEEK) to improve cell adhesion and osseointegration. Bio-activated PEEK constructs were designed with prepared surface of different layers of polystyrene sulfonate (PSS) and polyallylamine hydrochloride (PAH) multilayers. Irregular morphology was found on the 5 and 10-layer PEEK surfaces, while “island-like” clusters were observed for 20-layer (20 L) multilayers. Besides, the 20 L PEEK showed more hydrophilic feature than native PEEK, and the surface contact angle reduced from 39.7° to 21.7° as layers increased from 5 to 20. In vitro, modified PEEK allowed excellent adhesion and proliferation of bone marrow stromal cells, and induced higher cell growth rate and alkaline phosphatase level. In vivo, this bio-active PEEK exhibited significantly enhanced integration with bone tissue in an osteoporosis rabbit model. This work highlights layer-by-layer self-assembly as a practical method to construct bio-active PEEK implants for enhanced osseointegration.

A sensitive immunosensor for microcystin-(leucine–arginine) based on fluorescent self-assembled multilayers

In this paper, a novel fluorescent immunosensor based on self-assembled multilayers was constructed to detect microcystin-(leucine–arginine).

Electrophoretic Deposition of Ni(OH)2 Nanoplatelets Modified by Polyelectrolyte Multilayers: Study of the Coatings Formation in a Laminar Flow Cell

The electrophoretic deposition (EPD) of semiconductor ceramic nanoplatelets functionalized by self-assembled polyelectrolyte multilayers has been investigated. The influence of particle surface modification in the packing of the nanostructured film on a nickel cathode has been determined for different electrical conditions. A polymer multilayer shell has been fashioned onto β-Ni(OH)2 nanoplatelets surfaces by alternating the adsorption of Polyethylenimine (PEI) and Polyacrylic Acid (PAA). Two different core-shell systems with 1, 3 and 5 layers were considered using either linear or branched PEI as polycation to alternate with the anionic polyelectrolyte (PAA). The Layer by Layer, (LbL) build-up of polyanions and polycations was characterized both in terms of particle zeta potential measurements and in situ measurements of polyelectrolyte adsorption onto a flat substrate by optical fixed-angle reflectometry. The amount of polyelectrolyte required to build up each layer was determined from zeta potential measurements. Both data allowed the design of the in situ formation of the core-shell nanostructures as well as the shaping of the particulated coatings following the one-pot procedure, avoiding intermediate steps of drying or washing. The movement of the core-shell particles, their aggregation state and the coating growth during electrophoretic deposition were studied in situ using a laminar flow cell coupled to an optical microscope. The particle flux was calculated from the surface coverage of the cathode and compared to the values estimated by the EPD electrokinetic model, demonstrating the strong impact of the steric interactions between the core-shell particles in both the deposition rate of nanoplatelets and the coating morphology.