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PubMed2007

Amperometric glucose biosensor based on multilayer films via layer-by-layer self-assembly of multi-wall carbon nanotubes, gold nanoparticles and glucose oxidase on the Pt electrode.

A novel amperometric glucose biosensor based on the nine layers of multilayer films composed of multi-wall carbon nanotubes (MWCNTs), gold nanoparticles (GNp) and glucose oxidase (GOD) was developed for the specific detection of glucose. MWCNTs were chemically modified with the H(2)SO(4)-HNO(3) pretreatment to introduce carboxyl groups which were used to interact with the amino groups of poly(allylamine) (PAA) and cysteamine via 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide cross-linking reaction, respectively. A cleaned Pt electrode was immersed in PAA, MWCNTs, cysteamine and GNp, respectively, followed by the adsorption of GOD, assembling the one layer of multilayer films on the surface of Pt electrode (GOD/GNp/MWCNTs/Pt electrode). Repeating the above process could assemble different layers of multilayer films on the Pt electrode. PBS washing was applied at the end of each assembly deposition for dissociating the weak adsorption. Film assembling and characterization were studied by transmission electron microscopy and quartz crystal microbalance, and properties of the resulting glucose biosensors were measured by electrochemical measurements. The marked electrocatalytic activity of Pt electrode based on multilayer films toward H(2)O(2) produced during GOD enzymatic reactions with glucose permitted effective low-potential amperometric measurement of glucose. Taking the sensitivity and selectivity into consideration, the applied potential of 0.35 V versus Ag/AgCl was chosen for the oxidation detection of H(2)O(2) in this work. Among the resulting glucose biosensors, the biosensor based on nine layers of multilayer films was best. It showed a wide linear range of 0.1-10mM glucose, with a remarkable sensitivity of 2.527 microA/mM, a detection limit of 6.7 microM estimated at a signal-to-noise ratio of 3 and fast response time (within 7s). Moreover, it exhibited good reproducibility, long-term stability and the negligible interferences of ascorbic acid, uric acid and acetaminophen. The study can provide a feasible approach on developing new kinds of oxidase-based amperometric biosensors, and can be used as an illustration for constructing various hybrid structures.

Biosensing Techniques↗

PubMed2004

The effect of polyelectrolyte chain length on layer-by-layer protein/polyelectrolyte assembly--an experimental study.

The effect of polyelectrolyte chain length on the formation of multilayered assemblies of alternating globular proteins and linear polyanions prepared by the layer-by-layer electrostatic adsorption technique was investigated. The systems studied were albumin/sodium poly(styrenesulfonate), immunoglobulin G/sodium poly(styrenesulfonate), albumin/sodium dextran sulfate, and albumin/heparin. The formation of assemblies was followed using FTIR multiple internal reflection spectroscopy. While the amount of polyelectrolyte adsorbed on the first (primary) protein layer did not depend on its molecular weight, the effect of polyelectrolyte chain length was clearly observed in the following steps of alternating adsorption. Some short-chain polyanion molecules were removed from the surface when a next protein layer was adsorbed from solution. The short polyanion chains were not able to make a sufficient number of ion pairs for stable interaction with additional protein molecules and left the surface as soluble protein/polyanion complexes. The most pronounced effect could be seen with sodium poly(styrenesulfonate) of Mw up to ca. 2 x 10(4), but a detectable effect could be traced even up to Mw ca. 8 x 10(4). Such a pronounced effect, however, was not observed with dextran sulfate. The effect of molecular weight of heparin was clearly observed but all heparins tested, regardless of their molecular weight, effectively assembled with albumin to form multilayer.

Adsorption↗

PubMed2005

Deposition temperature effect on release rate of indomethacin microcrystals from microcapsules of layer-by-layer assembled chitosan and alginate multilayer films.

Indomethacin (IDM) microcrystals sized 5 approximately 10 microm were directly encapsulated with nature polysaccharides chitosan (CHI) and sodium alginate (ALG) through layer-by-layer (LbL) self-assembly. Due to partial dissolution of IDM in the deposition solution, the retention of the IDM microcrystals gradually decreased with increasing deposition times and became 47.7% as 10 layers of polysaccharides formed. The release rate of the IDM from the microcapsules was monitored with UV absorbance. The half release time t(1/2) of IDM in the microcapsule increased with the layer number and the initial burst phenomenon was relieved after encapsulation. It was found that added NaCl did not affect the release rate even up to 0.5 M of its concentration, while increasing the release temperature remarkably speeded up the release process. The prolonged release of the encapsulated IDM was still observed when the aqueous release solution containing 20 vol.% ethanol. It was very significant that increasing deposition temperature from 20 to 60 degrees C reduced the release rate efficiently, owing to the increase in multilayer thickness and formation of a more perfect multilayer film. This finding provides a new and simple method to control the permeability of the LbL assembled multilayer films. Because of the biodegradability of CHI and ALG and various methods to tune the release rate, the LbL self-assembly on drug microcrystals promises high potential for encapsulation used in controlled release.

Alginates↗

PubMed2006

Experimental and finite element modelling studies on single-layer and multi-layer 1-3 piezocomposite transducers.

Finite element modelling (FEM) using ATILA code and experimental studies have been carried out on 1-3 piezocomposite transducers. FEM study was initially carried out on a piezocomposite infinite plate and then extended to transducers of finite size. The infinite-plate model results agree well with that of a simple analytical model and experiments. The acoustic performance of multi-layer finite-size piezocomposite transducers was also studied. Transducer stacks were fabricated with different number of layers. The transducer characteristics such as the electrical impedance, the transmitting voltage response (TVR) and the receiving sensitivity (RS) of the 1-3 piezocomposite transducers were evaluated as functions of frequency, ceramic volume fractions and the number of layers. TVR increases and RS decreases with increase in ceramic volume fractions. The model results are found to agree with the experimental data, especially when the number of layers is less.

Journal Article↗

PubMed1999

Contaminant transfer during the coextrusion of tri-layer polymer films with a recycled layer. Effect of this transfer on the time of protection of the food.

Reusing old polymer packages as new food packages necessitates the coextrusion of tri-layer polymers, the old polymer being located between two virgin polymer layers. As it takes some time for the contaminant initially located in the old polymer, the virgin polymer layer acts upon the food pollution as a functional barrier. With the coextrusion process, the polymer layers are heated up to a high temperature and let cool down in air. During this coextrusion stage, the contaminant diffuses through the package at a fast rate over a short period of time. Then the time of protection of the functional barrier is significantly reduced. The process of the contaminant transfer is especially studied either during the coextrusion stage of the film or in the package-food system at room temperature.

Food Contamination↗

PubMed2002

Chemical microcharacterization of ultrathin iodide conversion layers and adsorbed thiocyanate surface layers on silver halide microcrystals with time-of-flight SIMS.

The technique of imaging time-of-flight secondary ion mass spectrometry (TOF-SIMS) and dual beam depth profiling has been used to study the composition of the surface of tabular silver halide microcrystals. Analysis of individual microcrystals with a size well below 1 microm from a given emulsion is possible. The method is successfully applied for the characterization of silver halide microcrystals with subpercent global iodide concentrations confined in surface layers with a thickness below 5 nm. The developed TOF-SIMS analytical procedure is explicitly demonstrated for the molecular imaging of adsorbed thiocyanate layers (SCN) at crystal surfaces of individual crystals and for the differentiation of iodide conversion layers synthesized with KI and with AgI micrates (nanocrystals with a size between 10 and 50 nm). It can be concluded that TOF-SIMS as a microanalytical, surface-sensitive technique has some unique properties over other analytical techniques for the study of complex structured surface layers of silver halide microcrystals. This offers valuable information to support the synthesis of future photographic emulsions.

Bromides↗

PubMed2002

Study of layer-by-layer self-assembled viscoelastic films on thickness-shear mode resonator surfaces.

We describe quartz crystal electroacoustic admittance studies in thickness shear mode resonators loaded with self-assembled multilayers composed of alternate layers of glucose oxidase (GOx) and poly(allylamine) covalently attached to [Os(bpy)2ClPyCOH]- , (PAH-Os), deposited on a 3-mercaptopropanesulfonic acid (MPS)-modified gold on the quartz crystal. The complex acoustic impedance parameters, R(S) and X(LS) of a lumped-element Butterworth-Van Dyke (BVD) resonator have been determined for organized thin films of different thickness obtained by varying the number of enzyme layers, n, in (PAH-Os)n(GOx)n structures. The ellipsometric film thickness and mass for dry enzyme multilayer films and films in contact with water were evaluated, and the average film density was estimated. By combination of the estimated film thickness and density, the expression for the surface mechanical impedance of the lumped-element modified resonator (Granstaff and Martin model), and the liquid density and viscosity, we simulate the layer-by-layer film growth on the basis of the measured electroacoustic impedance. The complex impedance X(LS) and R(S) increase with film thickness and the enzyme films can be regarded as acoustically thin in the reduced state for films thinner than 600 nm. We have also measured electroacoustic parameters for PAH-Os/GOx self-assembled multilayers under electrochemical perturbation in a buffer electrolytic solution. The electrostatically self-assembled multilayers behaved as lossy viscoelastic films at 10 MHz with G'f and G''f on the order of 10(6) Pa. The films became viscoelastic upon oxidation to Os(III), resulting in an increase of R(S) and X(LS) in the oxidized state with the number of (PAH-Os)(GOx) bilayers due to film swelling and an increase in the shear moduli during oxidation.

Allylamine↗

PubMedDate not supplied

Electrostatic adsorption of heme proteins alternated with polyamidoamine dendrimers for layer-by-layer assembly of electroactive films.

A novel thin film of heme proteins, including hemoglobin (Hb), myoglobin (Mb), and catalase (Cat), was successfully assembled layer by layer with polyamidoamine (PAMAM) dendrimers on different solid surfaces. At pH 7.0, protonated PAMAM possesses positive surface charges, whereas the proteins have net negative surface charges at pH above their isoelectric points. Thus, layer-by-layer {PAMAM/protein}(n)() films were assembled with alternate adsorption of oppositely charged PAMAM and proteins from their aqueous solutions mainly by electrostatic interaction. The assembly process was monitored by quartz crystal microbalance (QCM), UV-vis spectroscopy, and cyclic voltammetry (CV). The growth of the protein multilayer films was regular and linear, whereas the electroactivity of the films was only extended to a few bilayers. CVs of {PAMAM/protein}(n)() films showed a pair of well-defined and nearly reversible peaks characteristic of the protein heme Fe(III)/Fe(II) redox couples. Although {PAMAM/Hb}(n)() and {PAMAM/Mb}(n)() films showed very similar properties, {PAMAM/Cat}(n)() films displayed different and unique characters. The substrates with biological or environmental significance, such as oxygen, hydrogen peroxide, trichloroacetic acid, and nitrite, were catalytically reduced at {PAMAM/protein}(n)() film electrodes, showing the potential applicability of the films as new types of biosensors or bioreactors based on direct electrochemistry of the proteins. Both the electrochemical and electrocatalytic activity of {PAMAM/protein}(n)() films can be tailored precisely by controlling the number of bilayers or the film thickness.

Adsorption↗

PubMed2005

Immobilization of humic acid in nanostructured layer-by-layer films for sensing applications.

Humic acids (HAs), naturally occurring biomacromolecules, were incorporated into nanostructured polymeric films using the layer-by-layer (LbL) technique, in which HA layers were alternated with layers of poly(allylamine hydrochloride) (PAH). Atomic force microscopy (AFM) revealed very smooth films, with mean roughness varying from 0.89 to 1.19 nm for films containing 5 and 15 PAH/HA bilayers, respectively. The films displayed electroactivity, with the presence of only one reduction peak at ca. 0.675 V (vs Ag/AgCl). Such a well-defined electroactivity allowed the films to be used as highly sensitive pesticide sensors, with detection of pentachlorophenol (PCP) in solutions at concentrations as low as 10(-9) mol L(-1).

Biosensing Techniques↗

PubMed2004

Layer-by-layer assembled multilayer films of titanate nanotubes, Ag- or Au-loaded nanotubes, and nanotubes/nanosheets with polycations.

Aqueous suspensions of hydrothermally synthesized titanate nanotubes and poly(diallyldimethylammonium chloride) (PDDA) have been employed to fabricate multilayer films on various substrates in a layer-by-layer fashion. Atomic force microscopy displays the dense coverage of the substrate surface by the nanotubes. UV-vis absorption spectroscopy confirms the consecutive growth of PDDA/nanotube layer pairs. Single crystalline Ag and Au nanoparticles with narrow size distribution spatially correlating with the nanotubes have been obtained by treating the nanotubes with AgNO(3) or HAuCl(4) aqueous solution followed by chemical reduction. The noble metal nanoparticles show a strong surface plasmon absorption band. A multilayer film construction of the noble-metal-loaded nanotubes has also been achieved. This process has been further extended to the heteroassembly of nanotubes/nanosheets in different layer sequences.

Journal Article↗

PubMed2005

Persistence length control of the polyelectrolyte layer-by-layer self-assembly on carbon nanotubes.

We have studied layer-by-layer polyelectrolyte self-assembly on pristine individual single-wall carbon nanotubes as a function of solution ionic strength. We report the existence of an ionic strength threshold for the deposition, below which the majority of nanotubes remain uncoated. Once the ionic strength reaches the threshold value, the majority of the individual nanotubes become coated with polyelectrolytes. Our results indicate that the self-assembly process likely involves wrapping of polymer chains around nanotubes and that the polymer chain's ability to bend in order to accommodate the nanotube curvature is one of the critical parameters controlling layer-by-layer electrostatic self-assembly on these one-dimensional templates.

Electrochemistry↗

PubMed2005

Layer-by-layer assembly of polyoxometalates into microcapsules.

The polyoxometalate (POM) chemistry world has been experiencing an unparalleled development of rapid synthesis of new compounds and slow development of POM-based functional materials and devices. Meanwhile, researchers in the microcapsule world, encouraged by the introduction of the layer-by-layer method, are pursuing good components for constructing functional capsule devices. Here, in view of the versatile properties that POM-based microcapsules may possess, various types of POM-polyelectrolyte composite microcapsules were constructed using the layer-by-layer method. Microscopy reveals that polyoxometalates form nanoparticles on the shell in the presence of cationic polyelectrolytes. These nanoparticles connected with polyelectrolytes constitute the shell and support the microcapsule from collapse after drying, and this is an interesting characteristic different from those of common composite and polyelectrolyte capsules. Fourier transform infrared (FTIR), UV-vis absorption, and X-ray photoelectron spectroscopy (XPS) were used to examine the properties of the POMs in the microcapsules. The obtained microcapsules exhibit higher thermal stability than polyelectrolyte microcapsules. Furthermore, the functions of POMs were maintained when they were assembled into microcapsules. It is proved that microcapsules bearing POMs with redox activity can provide a reduction environment, which can lead to the realization of in situ synthesis of materials, and that microcapsules with photoluminescent POMs as a component can also have a photoluminescent property, providing a way to develop functional capsule devices. This work may provide an opportunity to enrich both the polyoxometalate chemistry and the capsule field.

Journal Article↗

PubMed2006

Fabrication of electroactive layer-by-layer films of myoglobin with gold nanoparticles of different sizes.

Alternate adsorption of oppositely charged myoglobin (Mb) and gold nanoparticles with different sizes were used to assemble {Au/Mb}n layer-by-layer films on solid surfaces by electrostatic interaction between them. The direct electrochemistry of Mb was realized in {Au/Mb}n films at pyrolytic graphite (PG) electrodes, showing a pair of well-defined, nearly reversible cyclic voltammetry (CV) peaks for the Mb heme FeIII/FeII redox couple. Quartz crystal microbalance (QCM), electrochemical impedance spectroscopy (EIS), and CV were used to monitor or confirm the growth of the films. Compared with other Mb layer-by-layer films with nonconductive nanoparticles or polyions, {Au/Mb}n films showed much improved properties, such as smaller electron-transfer resistance (Rct) measured by EIS with Fe(CN)3-/4- redox probe, higher maximum surface concentration of electroactive Mb (Gamma*max), and better electrocatalytic activity toward reduction of O2 and H2O2, mainly because of the good conductivity of Au nanoparticles. Because of the high biocompatibility of Au nanoparticles, adsorbed Mb in the films retained its near native structure and biocatalytic activity. The size effect of Au nanoparticles on the electrochemical and electrocatalytic activity of Mb in {Au/Mb}n films was investigated, demonstrating that the {Au/Mb}n films assembled with smaller-sized Au nanoparticles have smaller Rct, higher Gamma*max, and better biocatalytic reactivity than those with larger size.

Adsorption↗

PubMed2006

Enhanced charge transport and incorporation of redox mediators in layer-by-layer films containing PAMAM-encapsulated gold nanoparticles.

In this work, we exploit the molecular engineering capability of the layer-by-layer (LbL) method to immobilize layers of gold nanoparticles on indium tin oxide (ITO) substrates, which exhibit enhanced charge transfer and may incorporate mediating redox substances. Polyamidoamine (PAMAM generation 4) dendrimers were used as template/stabilizers for Au nanoparticle growth, with PAMAM-Au nanoparticles serving as cationic polyelectrolytes to produce LbL films with poly(vinylsulfonic acid) (PVS). The cyclic voltammetry (CV) of ITO-PVS/PAMAM-Au electrodes in sulfuric acid presented a redox pair attributed to Au surface oxide formation. The maximum kinetics adsorption is first-order, 95% of the current being achieved after only 5 min of adsorption. Electron hopping can be considered as the charge transport mechanism between the PVS/PAMAM-Au layers within the LbL films. This charge transport was faster than that for nonmodified electrodes, shown by employing hexacyanoferrate(III) as the surface reaction marker. Because the enhanced charge transport may be exploited in biosensors requiring redox mediators, we demonstrate the formation of Prussian blue (PB) around the Au nanoparticles as a proof of principle. PAMAM-Au@PB could be easily prepared by electrodeposition, following the ITO-PVS/ PAMAM-Au LbL film preparation procedure. Furthermore, the coverage of Au nanoparticles by PB may be controlled by monitoring the oxidation current.

Journal Article↗

PubMed2004

Driving forces for layer-by-layer self-assembly of films of SiO2 nanoparticles and heme proteins.

Heme protein hemoglobin (Hb) or myoglobin (Mb) and silica nanoparticles in a variety of charge states were assembled layer-by-layer into films on solid surfaces to investigate the driving forces for film assembly. Cyclic voltammetry (CV), quartz crystal microbalance (QCM), X-ray photoelectron spectroscopy (XPS), and UV-vis and reflectance absorption infrared (RAIR) spectroscopy were used to characterize the different [SiO2/protein]n films. Even when the proteins and silica were both negatively charged, stable layer-by-layer [SiO2/protein]n films were successfully fabricated, although amounts of protein were smaller than when nanoparticles and proteins had opposite charges. Results suggest the importance of localized Coulombic attractions between the negative nanoparticle surface and positively charged amino acid residues on the Mb or Hb surfaces in the assembly and for the stability of [SiO2/protein]n films.

Amino Acids↗

PubMed2004

Layer-by-Layer electrostatic self-assembly of polyelectrolyte nanoshells on individual carbon nanotube templates.

Carbon nanotubes have been featured prominently in the nanotechnology research for some time, yet robust strategies for noncovalent chemical modification of the nanotube surface are still missing. Such strategies are essential for the creation of functional device architectures. Here, we present a new general procedure for carbon nanotube modification based on polyelectrolyte layer-by-layer assembly. We have built multilayer structures around individual carbon nanotube bridges by first modifying the nanotube surface with a pyrene derivative followed by layer-by-layer deposition of polyelectrolyte macroions on the nanotube. Transmission electron microscopy and scanning confocal fluorescence microscopy images confirm the formation of nanometer-thick amorphous polymer nanoshells around the nanotubes. These multilayer polyelectrolyte shells on individual carbon nanotubes introduce nearly unlimited opportunities for the incorporation of various functionalities into nanotube devices, which, in turn, opens up the possibility of building more complex multicomponent structures.

Journal Article↗

PubMed2006

The role of Azopolymer/Dendrimer layer-by-layer film architecture in photoinduced birefringence and the formation of surface-relief gratings.

The fabrication of nanostructured layer-by-layer (LbL) films strives for molecular control of the film properties directly connected with modifications in the film architecture. In the present report, the photoinduced birefringence and formation of the surface-relief gratings in LbL films obtained with an azopolymer (PS119) are shown to be strongly affected by the generation of the dendrimer employed in the alternating layers. Stronger adsorption of PS119 occurred when polypropylenimine tetrahexacontaamine dendrimer (DAB) of higher generations is used, due to a larger number of sites available to interact with azochromophores in PS119. In contrast, the photoinduced birefringence for LbL films made with the generation 1 dendrimer (DABG1) was higher, which can be explained by weaker interactions between adjacent layers. Strong interactions in LbL films consisting of PS119 and generation 3 or 5 dendrimers restrict the chromophore mobility, leading to a smaller birefringence. The interpretation is supported by the fact that surface-relief gratings with larger amplitudes were obtained for 35-bilayer films of DABG1/PS119 (31 nm) in comparison with films from DABG5/PS119 (5 nm). These gratings were formed with mass transport arising from a light-driven mechanism, as photoinscription was successful only with p-polarized light and not with s-polarized light.

Journal Article↗

PubMed2006

Layer-by-layer-assembled microfiltration membranes for biomolecule immobilization and enzymatic catalysis.

Multilayer assemblies of polyelectrolytes, for protein immobilization, have been created within the membrane pore domain. This approach was taken for two reasons: (1) the high internal membrane area can potentially increase the amount of immobilized protein, and (2) the use of convective flow allows uniform assembly of layers and eliminates diffusional limitations after immobilization. To build a stable assembly, the first polyelectrolyte layer was covalently attached to the membrane surface and inside the pore walls. Either poly(L-glutamic acid) (PLGA) or poly(L-lysine) (PLL) was used in this step. Subsequent deposition occurs by multiple electrostatic interactions between the adsorbing polyelectrolyte [poly(allylamine) hydrochloride (PAH) or poly(styrenesulfonate) (PSS)] and the oppositely charged layer. Three-layer membranes were created: PLL-PSS-PAH or PLGA-PAH-PSS, for an overall positive or negative charge, respectively. The overall charge on both the protein and membrane plays a substantial role in immobilization. When the protein and the membrane are oppositely charged, the amount immobilized and the stability within the polyelectrolyte assembly are significantly higher than for the case when both have similar charges. After protein incorporation in the multilayer assembly, the active site accessibility was comparable to that obtained in the homogeneous phase. This was tested by affinity interaction (avidin-biotin) and by carrying out two reactions (catalyzed by glucose oxidase and alkaline phosphatase). Besides simplicity and versatility, the ease of enzyme regeneration constitutes an additional benefit of this approach.

Adsorption↗