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PubMed2001

Fabrication of layer-by-layer deposited multilayer films containing DNA and its interaction with methyl green.

Multilayer films were fabricated by layer-by-layer electrostatic deposition techniques between poly(diallyldimethylammonium chloride) (PDDA) and calf thymus DNA (CT DNA) on glassy carbon and quartz substrates. Electrochemical impedance spectroscopy (EIS), Fourier transform infrared (FTIR) spectroscopy and UV-vis spectroscopy demonstrated the uniform assembly of PDDA/DNA multilayer films, and X-ray photoelectron spectroscopy confirmed the elemental composition of the films. Moreover, the interaction of DNA in PDDA/DNA films with methyl green was investigated by UV-vis spectroscopy and circular dichroism (CD).

Animals↗

PubMed1997

NADPH-diaphorase reactivity is reduced in the molecular layer but increased in the granular layer of primate cerebellum after prolonged anaesthesia.

To test if nitric oxide (NO) is involved in modulation of neuronal activity after global changes of brain function, nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) reactivity in the cerebellar cortex was compared in monkeys maintained under anaesthesia for 24-48 h with others only anaesthetised for perfusion. After prolonged anaesthesia, NADPH-d activity was reduced in the molecular layer, but increased in the granular layer, with the maintenance of a parasagittal patchy organisation of the highly reactive granule cells. Selective labelling of NADPH-d in the infraganglionic plexuses deep to a subset of Purkinje cell somata was lost in the anaesthetised animals. This differential alteration of NADPH-d reactivity suggests that NO may play a role in regulation of neuronal and synaptic activity during anaesthesia.

Anesthesia↗

PubMed2000

Convergence property of topographic mapping formation from cell layer to cell layer through correlation learning rule.

To elucidate the mechanism of topographic organization, we propose a simple topographic mapping formation model from one-dimensional cell layer to one-dimensional cell layer. In our model, each cell takes a binary state value and we consider several learning principles which are extensions of Hebb's rule. We pay special attention to a correlation learning rule where a synaptic weight value is increased if pre- and post-synaptic cells' state values are the same. First, we show that under a certain network size condition, a mapping is stable with respect to the correlation learning if and only if it is topographic. Second, we introduce a special class of weight matrices called band type and show that the set of band type weight matrices is strongly closed and such a weight matrix cannot yield a topographic mapping. Third, we show that any mapping, if it is defined by a non band type weight matrix, converges to a topographic mapping. The proof method is intrinsically of combinatorial nature in a framework of Markov process.

Algorithms↗

PubMed2003

Encapsulation of glucose oxidase microparticles within a nanoscale layer-by-layer film: immobilization and biosensor applications.

We report on an immobilization strategy utilizing layer-by-layer encapsulated microparticles of enzymes within a nanoscale polyelectrolyte film. Encapsulation of glucose oxidase (GOD) microparticles was achieved by the sequential adsorption of oppositely charged polyelectrolytes onto the GOD biocrystal surface. The polyelectrolyte system polyallylamine/polystyrene sulfonate was used under high salt conditions to preserve the solid state of the highly water soluble GOD biocrystals during the encapsulation process. The resulting polymer multilayer capsule of about 15 nm wall thickness is permeable for small molecules (glucose), but non-permeable for macromolecules thus preventing the enzyme from leakage and at the same time shielding it from the outer environment e.g., from protease or microbial activity. Decrease of the buffer salt concentration leads to the dissolution of the enzyme under formation of mu-bioreactors. The spherical mu-bioreactors are bearing an extremely high loading of biocompound per volume. Encapsulated GOD was subsequently used to construct a biosensor by nanoengineered immobilisation of mu-bioreactor capsules onto an electrode surface. The presented approach demonstrates a general method to encapsulate highly soluble solid biomaterials and an immobilization strategy with the potential to create highly active thin and stable films of biomaterial.

Biosensing Techniques↗

PubMed2001

Amplification of amperometric biosensor responses by electrochemical substrate recycling. 3. Theoretical and experimental study of the phenol-polyphenol oxidase system immobilized in Laponite hydrogels and layer-by-layer self-assembled structures.

The amperometric response toward phenol of PPO-based rotating disk bioelectrodes is analyzed on the basis of a kinetic model taking into account internal and external mass transport effects and a CEC' electroenzymatic mechanism. Monophenolase activity of PPO catalyses the oxidation of phenol to o-quinone (step C). o-Quinone can then enter an amplification recycling process involving electrochemical reduction (step E) and enzymatic reoxidation (step C': catecholase activity). The rate-limiting steps such as monophenolase activity, catecholase recycling, permeability of the membrane, and activity and accessibility of the catalytic enzyme sites are theoretically considered and experimentally demonstrated for different electrode configurations including PPO immobilized in Laponite hydrogels and layer-by-layer self-assembled multilayers of PPO and poly(diallyldimethylammonium).

Biosensing Techniques↗

PubMed2004

Layer-by-layer self-assembly of multilayer zirconia nanoparticles on silica spheres for HPLC packings.

A novel zirconia-based HPLC packing material, ZrO2/SiO2, which consists of micrometer-sized silica spheres as core and nanometer-sized zirconia particles as surface coating, was prepared by a layer-by-layer self-assembly technique. The material exhibits favorable characteristics for HPLC applications, including high surface area and pore volume, good pore structure, narrow particle size, and pore size distribution. Not only the support ZrO2/SiO2 but also the stationary-phase C18 bonded ZrO2/SiO2 exhibits excellent chemical stability. In addition, good permeability was observed for both of them. High specific area surface and good permeability of ZrO2/SiO2 permit a high loading amount of chiral polymer on it and greatly improved the enantioselectivity and resolution for some chiral separations.

Journal Article↗

PubMed2004

Controlled layer-by-layer formation of ultrathin TiO2 on silver island films via a surface sol-gel method for surface-enhanced Raman scattering measurement.

A surface sol-gel process has been demonstrated to be an effective method for the surface modification of silver island films as unique SERS substrates for monitoring molecular adsorption on a dielectric titania surface. This layer-by-layer approach allows control of the thickness of the dielectric surface with a monolayer precision on silver surfaces. The enhancement of Raman scattering from adsorbed Rhodamine 6G molecules is inversely proportional to the thickness of the titania film, which is consistent with the decay of electromagnetic enhancement. Despite a reduction in the sensitivity of the film, a substantial improvement in the film was achieved as a result of the enhanced stability of this substrate compared to the silver island film without a TiO(2) coating.

Fluorescent Dyes↗

PubMedDate not supplied

Bioactive thin film of acidic fibroblast growth factor fabricated by layer-by-layer assembly.

A new class of bioactive thin films using growth factors as building blocks has been fabricated via layer-by-layer assembly (LBL) technique. Acid fibroblast growth factor (aFGF) in the presence of heparin was used as negatively charged polyelectrolytes, while poly(ethyleneimine) (PEI) was chosen as a positively charged counterpart. The self-deposition process and surface morphology of the resultant multilayers were monitored and detected by UV-vis absorbance spectra, advanced contact angle measurements, and scanning force microscopy (SFM) observations. Cell culture was performed to assess the efficiency of the growth factors. The fibroblasts proliferated faster on the surface assembled with five bilayers of (aFGF/heparin)/PEI with apparent higher cytoviability than on those surfaces modified by one bilayer of (aFGF/heparin)/PEI, five bilayers of aFGF/PEI, or five bilayers of heparin/PEI, and tissue culture polystyrene. Enhanced secretion of collagen type I and interleukin 6 (IL-6) by the fibroblasts seeded on the five bilayers of (aFGF/heparin)/PEI was also verified by immunohistochemical examination. The bioactivity of the (aFGF/heparin)/PEI multilayers could be largely preserved when stored at -20 degrees C.

Cell Proliferation↗

PubMed2001

Assembly of alternating polycation and DNA multilayer films by electrostatic layer-by-layer adsorption.

The assembly of alternating DNA and positively charged poly(dimethyldiallylammonium chloride) (PDDA) multilayer films by electrostatic layer-by-layer adsorption has been studied. The real-time surface plasmon resonance (BIAcore) technique was used to characterize and monitor the formation of multilayer films in solution in real time continuously. Electrochemical impedance spectroscopy (EIS) and UV-vis absorbance measurements were also used to study the film assembly, and linear film growth was observed. All the results indicate that the uniform multilayer can be obtained on the poly(ethylenimine)- (PEI-) coated substrate surface. The kinetics of the adsorption of DNA on PDDA surface was also studied by the real-time BIAcore technique; the observed rate constant was calculated using a Langmuir model (k(obs) = (1.28 +/- 0.08) x 10(-2) s(-1).

Adsorption↗

PubMedDate not supplied

Assembly of electroactive layer-by-layer films of hemoglobin and polycationic poly(diallyldimethylammonium).

Layer-by-layer (PDDA/Hb)(n) films were assembled by alternate adsorption of positively charged poly(diallyldimethylammonium) (PDDA) and negatively charged hemoglobin (Hb) at pH 9.2 from their aqueous solutions on pyrolytic graphite electrodes and other substrates. The assembly process was monitored and confirmed by quartz crystal microbalance (QCM), UV-vis spectroscopy, and cyclic voltammetry (CV). CVs of (PDDA/Hb)(n) films showed a pair of well-defined, nearly reversible peaks at about -0.34 V vs SCE at pH 7.0, characteristic of Hb heme Fe(III)/Fe(II) redox couple. Positions of Soret absorption band and infrared amide II band of Hb in (PDDA/Hb)(8) films suggest that Hb in the films keeps its secondary structure similar to its native state. The electrochemical parameters of (PDDA/Hb)(8) films were estimated by square wave voltammetry, and the thickness of the PDDA/Hb bilayer was estimated by QCM and scanning electron microscopy. Trichloroacetic acid and nitrite (NO(2)(-)) were catalytically reduced at (PDDA/Hb)(8) film electrodes. The electrochemical catalytic reactions of O(2) and H(2)O(2) on (PDDA/Hb)(8) films were also studied.

Catalysis↗

PubMedDate not supplied

Electrostatic layer-by-layer nanoassembly on biological microtemplates: platelets.

Platelets were coated with 78-nm silica nanoparticles, 45-nm fluorescent nanospheres, or bovine immunoglobulin G (IgG) through layer-by-layer assembly by alternate adsorption with oppositely charged linear polyions. Sequential deposition on platelet surfaces of cationic poly(dimethyldiallylammonium chloride) and anionic poly(styrene sulfonate) was followed by adsorption of nanoparticles or immunoglobulins. Nano-organized shells of platelets were demonstrated by transmission electron microscopy and fluorescence microscope images. Bovine IgG was assembled on platelets, as verified with anti-bovine IgG-FITC labeling. Localized targeting of anti-IgG shelled platelets was also demonstrated. An ability to coat blood cells with nano-organized shells can have applications in cardiovascular research and targeted drug delivery.

Adsorption↗

PubMedDate not supplied

Layer-by-layer engineering of biocompatible, decomposable core-shell structures.

The objective of the present investigation was to fabricate composite colloidal particles consisting of a sacrificial, decomposable template of biodegradable nature covered with biocompatible polyelectrolyte multilayers using the layer-by-layer sequential adsorption technique. Poly-dl-lactic acid and poly(dl-lactic-co-glycolic acid) were chosen to design the microparticulate template, and a preliminary feasibility study was carried out with poly(styrene sulfonate sodium)-poly(allylamine hydrochloride) as shell components. The properties of both core-shell and hollow structures obtained by core dissolution were characterized by confocal laser scanning microscopy, microelectrophoresis, scanning force microscopy, and scanning electron microscopy. The concept was then extended to biocompatible polyelectrolytes as shell wall building blocks to deduce stable hollow capsules with tailored properties. Uniform, complete coating with oppositely charged polyelectrolyte pairs was achieved for all the combinations investigated. The results demonstrate that polyester microparticles could serve as viable alternative components to conventionally employed templates to derive hollow capsules with defined size, shape, and shell thickness. With all the components used for fabrication being biocompatible, these polyelectrolyte capsules may find interesting applications in the fields of biology, biochemistry, biotechnology, and drug delivery.

Biocompatible Materials↗

PubMedDate not supplied

Site-selective lateral multilayer assembly of bienzyme with polyelectrolyte on ITO electrode based on electric field-induced directly layer-by-layer deposition.

We describe here a new approach to construct a multilayer enzyme/polyelectrolyte film on a structured transparent indium-tin oxide (ITO) covered glass electrode surface as micropattern, on which two different types of enzyme distributed laterally on one common substrate without interference. The multilayer film was prepared by alternate electric field directed layer-by-layer assembly deposition and alternate deposition of different redox enzymes and polyelectrolyte poly(diallyldimethylammonium chloride) (PDDA) onto the site-selective ITO glass electrode surface. The cyclic voltammogram, obtained from the ITO glass electrode modified with the glucose oxidase (GO(X))/PDDA and catalase (CA(T))/PDDA multilayers, revealed that the bioelectrocatalytic response is directly correlated to the number of deposition bilayers. From the analysis of cyclic voltammetric characterization, the coverage of catalytically active enzymes per enzyme/PDDA bilayer during the multilayer formation was homogeneous, which demonstrates that the multilayer is constructed in a spatially ordered manner. Also, from the atomic force microscopy and Brewster angle microscopy measurements, more information of the multilayer constructed by different methods on the modified electrode surface is obtained and compared. This fabrication technique is simple and would be applicable to the construction of a thickness- and area-controlled biopattern composed of multi-enzymes as well as multiple biomaterials.

Biosensing Techniques↗

PubMedDate not supplied

Disintegration of layer-by-layer assemblies composed of 2-iminobiotin-labeled poly(ethyleneimine) and avidin.

A layer-by-layer thin film composed of avidin and 2-iminobiotin-labeled poly(ethyleneimine) (ib-PEI) was prepared and their sensitivity to the environmental pH and biotin was studied. The avidin/ib-PEI multilayer assemblies were stable at pH 8-12, whereas the assemblies were decomposed at pH 5-6 due to the low affinity of the protonated iminobiotin residue to avidin. The avidin/ib-PEI assemblies can be disintegrated upon addition of biotin and analogues in the solution as a result of the preferential binding of biotin or analogues to the binding site of avidin. The decomposition rate was arbitrarily controlled by changing the type of stimulant (biotin or analogues) and its concentration. The avidin/ib-PEI assemblies were disintegrated rapidly by the addition of biotin or desthiobiotin, whereas the rate of decomposition was rather slow upon addition of lipoic acid or 2-(4'-hydroxyphenylazo)benzoic acid. The present system may be useful for constructing the stimuli-sensitive devices that can release drug or other functional molecules.

Avidin↗

PubMedDate not supplied

Molecularly engineered nanocomposites: layer-by-layer assembly of cellulose nanocrystals.

Cellulose nanocrystals are promising as a new class of reinforcing material for the preparation of nanostructured composites. We report here the preparation of cellulose nanocrystal multilayer composites with poly(diallyldimethylammonium chloride) using layer-by-layer assembly (LBL) technique. The LBL assembly was characterized with UV-Vis spectroscopy and ellipsometry. The average thickness of a single bilayer was found to be 11 nm. AFM and SEM characterization revealed uniform coverage and densely packed cellulose crystal surface.

Biocompatible Materials↗

PubMed2006

A blank slate? Layer-by-layer deposition of hyaluronic acid and chitosan onto various surfaces.

Although poly(alpha-hydroxy esters), especially the PLGA family of lactic acid/glycolic acid copolymers, have many properties which make them promising materials for tissue engineering, the inherent chemistry of surfaces made from these particular polymers is problematic. In vivo, they promote a strong foreign-body response as a result of nonspecific adsorption and denaturation of serum proteins, which generally results in the formation of a nonfunctional fibrous capsule. Surface modification post-production of the scaffolds is an often-utilized approach to solving this problem, conceptually allowing the formation of a scaffold with mechanical properties defined by the bulk material and molecular-level interactions defined by the modified surface properties. A promising concept is the so-called "blank slate": essentially a surface that is rendered resistant to nonspecific protein adsorption but can be readily activated to covalently bind bio-functional molecules such as extracellular matrix proteins, growth factors or polysaccharides. This study focuses on the use of the quartz crystal microbalance (QCM) to follow the layer-by-layer (LbL) electrostatic deposition of high molecular weight hyaluronic acid and chitosan onto PLGA surfaces rendered positively charged by aminolysis, to form a robust, protein-resistant coating. We further show that this surface may be further functionalized via the covalent attachment of collagen IV, which may then be used as a template for the self-assembly of basement membrane components from dilute Matrigel. The response of NIH-3T3 fibroblasts to these surfaces was also followed and shown to closely parallel the results observed in the QCM.

3T3 Cells↗

PubMed2006

Fabrication of protein nanotubes based on layer-by-layer assembly.

Nanotubes of cytochrome C (cyto-c) with glutaraldehyde (GA) or PSS based on the layer-by-layer (LbL) assembly through covalent binding and electrostatic adsorption have been fabricated. The combination of the template method and the LbL method for fabrication of nanotubes exhibits low cost, simplicity, and versatility. The tubular morphology of the assembled glutaraldehyde and cytochrome C film was demonstrated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements. The components of the tubes were determined by energy-dispersive X- ray spectra (EDAX). It is found that the assembled tubes keep the proteins' biochemical activity and electronic activity by cyclic voltammograms. The measurements of ultraviolet spectra and circular dichroism (CD) on the assembled nanotubes confirmed the cyto-c existence in the tubes.

Absorption↗

PubMed2000

Organic-inorganic perovskites containing trivalent metal halide layers: the templating influence of the organic cation layer.

Thin sheetlike crystals of the metal-deficient perovskites (H2AEQT)M2/3I4 [M = Bi or Sb; AEQT = 5,5"'-bis-(aminoethyl)-2,2':5',2'':5'',2'''-quaterthiophene] were formed from slowly cooled ethylene glycol/2-butanol solutions containing the bismuth(III) or antimony(III) iodide and AEQT.2HI salts. Each structure was refined in a monoclinic (C2/m) subcell, with the lattice parameters a = 39.712(13) A, b = 5.976(2) A, c = 6.043(2) A, beta = 92.238(5) degrees, and Z = 2 for M = Bi and a = 39.439(7) A, b = 5.952(1) A, c = 6.031(1) A, beta = 92.245(3) degrees, and Z = 2 for M = Sb. The trivalent metal cations locally adopt a distorted octahedral coordination, with M-I bond lengths ranging from 3.046(1) to 3.218(3) A (3.114 A average) for M = Bi and 3.012(1) to 3.153(2) A (3.073 A average) for M = Sb. The new organic-inorganic hybrids are the first members of a metal-deficient perovskite family consisting of (Mn+)2/nV(n-2)/nX4(2-) sheets, where V represents a vacancy (generally left out of the formula) and the metal cation valence, n, is greater than 2. The organic layers in the AEQT-based organic-inorganic hybrids feature edge-to-face aromatic interactions among the rigid, rodlike quaterthiophene moieties, which may help to stabilize the unusual metal-deficient layered structures.

Journal Article↗