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At least 163 records · Page 9Linked to original sources

PubMed2005

Comparative bioelectrochemical study of core-shell nanocluster films with ordinary layer-by-layer films containing heme proteins and CaCO3 nanoparticles.

Negatively charged heme protein hemoglobin (Hb) or myoglobin (Mb) at pH 9.0 and positively charged poly(diallyldimethylammonium) (PDDA) were alternately adsorbed on the surface of CaCO(3) nanoparticles, forming core-shell CaCO(3)-[PDDA/(protein/PDDA)(m)] ([protein-m]) nanoclusters. Oppositely charged [protein-m] and poly(styrenesulfonate) (PSS) were then assembled layer by layer on various solid substrates, forming {[protein-m]/PSS}(n) films. In the meantime, ordinary layer-by-layer films of heme proteins with CaCO(3) nanoparticles ({protein/CaCO(3)}(n)) were also grown on solid surfaces. Transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) spectroscopy, quartz crystal microbalance (QCM), and cyclic voltammetry (CV) were used to characterize the nanoclusters and monitor the growth of the two types of films. Both kinds of protein films assembled on pyrolytic graphite (PG) electrodes exhibited well-defined, nearly reversible CV reduction-oxidation peaks, characteristic of heme Fe(III)/Fe(II) redox couples, and were used to catalyze the electrochemical reduction of hydrogen peroxide. The {[protein-m]/PSS}(n) films demonstrate distinct advantages over the {protein/CaCO(3)}(n) films due to their larger fraction of electroactive proteins, higher catalytic efficiency, and better thermostability. The penetration experiments of the electroactive probe into these films indicate that the {[protein-m]/PSS}(n) nanocluster films possess more pores or channels than the simple {protein/CaCO(3)}(n) films, which may be beneficial to counterion transport in the charge-hopping mechanism and helpful for the diffusion of catalysis substrates into the films. In addition, the electrochemical and biocatalytic activity of protein nanocluster films can be tailored by controlling the number of bilayers assembled on the nanoparticle cores (m) as well as the film thickness or the number of nanocluster layers on the electrodes (n).

Biochemistry↗

PubMed2004

Layer-by-layer self-assembly of multilayer films containing DNA and Eu3+: their characteristics and interactions with small molecules.

Thin films of alternating DNA and rare earth ion Eu3+ layers from dilute aqueous solutions were fabricated onto quartz substrates and silicon wafers through the layer-by-layer (LbL) self-assembly technique. UV-visible spectroscopy shows that a uniform layer of DNA can be fully adsorbed onto each alternate Eu3+ layer. Microscopic FTIR spectra show Eu3+ interacts with both the phosphate groups and nitrogenous bases of DNA, and the formation of [DNA/Eu]n films induces a change of the conformation of the DNA secondary structure to a certain extent. Various parameters affecting the DNA or Eu3+ loading into the composite film were investigated with emphasis on the effect of the pH and ionic strength of the DNA solution used for the film preparation. Atomic force microscopy was utilized to observe the morphologies of the DNA in the films obtained at two different pH values. Small molecules, such as alpha-tenoyltrifluoroacetone (TTA), Hoechst 33258 (Hoe), and ethidium bromide (EB), are all observed to interact with Eu3+ or DNA in the [DNA/Eu]n films. The [DNA/Eu]n films incorporated with these molecules show different fluorescent characteristics, and the fluorescence intensity of the films versus the bilayer number has a good linear relationship, confirming the potential for creating a different luminescence ability of the multilayer by controlling the number of DNA/Eu bilayers.

Adsorption↗

PubMed2005

In situ layer-by-layer film formation kinetics under an applied voltage measured by optical waveguide lightmode spectroscopy.

Layer-by-layer (LbL) thin film assembly occurs via the alternate adsorption of positively and negatively charged macromolecular species. We investigate here the control of LbL film growth through the electric potential of the underlying substrate. We employ optical waveguide lightmode spectroscopy (OWLS) to obtain in situ kinetic measurements of poly(allylamine hydrochloride)/poly(sodium 4-styrenesulfonate) (PAH/PSS) and poly(L-lysine)/dextran sulfate (PLL/DXS) multilayer film formation in the presence of an applied voltage difference (deltaV) between the adsorbing substrate, an indium tin oxide- (ITO-) coated waveguiding sensor chip, and a parallel platinum counterelectrode. We find initial layer adsorption to be significantly enhanced by an applied potential for both polyelectrolyte systems: the mass and thickness of (positively charged) PAH and PLL layers on ITO are about 60% and 500% larger, respectively, at deltaV = 2 V than at open circuit potential (OCP), in apparent violation of electrostatics. A kinetic analysis reveals the initial attachment rate constant to decrease with voltage, in agreement with electrostatics. To reconcile these results, we propose a more coiled and loosely bound adsorbed polymer conformation at higher applied potential. Following 10 adsorption steps, the mass and thickness of a PAH/PSS film grown under deltaV = 2 V are about 15% less than those of a comparable film grown under OCP, reflecting a lower degree of complexation between adsorbing polyanions and more highly coiled adsorbed polycations. Following 14 adsorption steps, the mass and thickness of a PLL/DXS film grown under deltaV = 2 V are about 70% greater than those of a comparable film grown under OCP, reflecting the increased charge overcompensation in the initial layer. We find the scaling of film mass () with the number of adsorption steps (n) to be linear in the PAH/PSS system and exponential (i.e., approximately eyn) in the PLL/DXS system, irrespective of applied voltage. We observe to decrease with applied voltage and to exhibit a crossover to a smaller value around n = 5. Extrapolation reveals PLL/DXS multilayer films to be suppressed by increased voltage in the limit of large n: the mass of films grown at OCP and deltaV = 1 V would surpass that of a film grown under deltaV = 2 V at about the 23rd and 18th adsorption steps, respectively. The formation kinetics of PLL/DXS, but not PAH/PSS, change qualitatively under voltage: PLL adsorption is slow to reach a plateau, possibly due to the formation of secondary structure, and a decrease in film mass occurs toward the end of each DXS adsorption step, suggesting spontaneous removal of some PLL/DXS complexes from the film.

Journal Article↗

PubMed2005

Stimuli-sensitive thin films prepared by a layer-by-layer deposition of 2-iminobiotin-labeled poly(ethyleneimine) and avidin.

Layered thin films composed of avidin and 2-iminobiotin-labeled poly(ethyleneimine) (ib-PEI) were prepared by a layer-by-layer deposition of avidin and ib-PEI on a solid surface, and the disintegration induced by changing environmental pH and adding biotin in the solution was studied. The avidin/ib-PEI layered film could be deposited only from the solutions of pH 10-12. The film did not form in pH 9 or more acidic media because of a low affinity of protonated 2-iminobiotin residues in ib-PEI to avidin. The avidin/ib-PEI layered films were stable in pH 8-12 solutions, while in pH 5-7 media the film decomposed spontaneously as a result of the protonation to 2-iminobiotin residues in ib-PEI. The avidin/ib-PEI films were disintegrated also upon addition of biotin and analogues in the solution owing to 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 films were disintegrated rapidly by addition of 10(-)(5) M of biotin or desthiobiotin, while the rate was slower upon adding the same concentration of lipoic acid or 2-(4'-hydroxyphenylazo)benzoic acid. On the other hand, the film was fully decomposed within 1 min in the 10(-)(3) M lipoic acid or 2-(4'-hydroxyphenylazo)benzoic acid solution. Thus, the decomposition rate is highly dependent on the concentration of the stimulants. It was observed that the stimuli-induced decomposition of the films is slow at pH 12, in contrast to a rapid decomposition in pH 8 medium due to a low affinity of the protonated 2-iminobiotin to avidin. The present system may be useful for constructing stimuli-sensitive devices that can release drug or other functional molecules.

Avidin↗

PubMed2005

van der Waals layer-by-layer construction of a carbon nanotube 2D network.

The acid-treated single-walled carbon nanotubes (SWCNTs) dispersed in water are only kinetically stable with electrostatic double layer repulsions just balancing against van der Waals (VDW) attractions. Introducing any external factor to disturb this balance causes immediate coagulation of SWCNTs. Here, an amine-covered flat substrate was immersed in the dispersion to initiate adsorption of SWCNTs onto the substrate surface. By repeating an adsorption-rinse-dry cycle, it was possible to deposit SWCNT bundles in a layer-by-layer fashion and to develop a 2D network consisting only of SWCNTs that are held by VDW interaction. We show that (1) adsorbed solution-grown aggregates are not relevant for the network connectivity, (2) 2D percolation takes place at very low surface coverage, (3) the electrical resistivity follows a power law against the layering cycles, (4) not only the adsorbed amount but also the added amount per layering cycle increases linearly with the SWCNT concentration, and (5) after the adsorption is initiated by amines, VDW attraction takes over for subsequent adsorption, with the consequence that the newly adsorbed SWCNTs are used to thicken each arm of the network rather than to cover more free surfaces.

Journal Article↗

PubMed2006

Layer-by-layer electrostatic self-assembly of single-wall carbon nanotube polyelectrolytes.

We have used anionic and cationic single-wall carbon nanotube polyelectrolytes (SWNT-PEs), prepared by the noncovalent adsorption of ionic naphthalene or pyrene derivatives on nanotube sidewalls, for the layer-by-layer self-assembly to prepare multilayers from carbon nanotubes with polycations, such as poly(diallyldimethylammonium) or poly(allylamine hydrochloride) (PDADMA or PAH, respectively), and polyanions (poly(styrenesulfonate), PSS). This is a general and powerful technique for the fabrication of thin carbon nanotube films of arbitrary composition and architecture and allows also an easy preparation of all-SWNT (SWNT/SWNT) multilayers. The multilayers were characterized with vis-near-IR spectroscopy, X-ray photoelectron spectroscopy (XPS), surface plasmon resonance (SPR) measurements, atomic force microscopy (AFM), and imaging ellipsometry. The charge compensation in multilayers is mainly intrinsic, which shows the electrostatic nature of the self-assembly process. The multilayer growth is linear after the initial layers, and in SWNT/polyelectrolyte films it can be greatly accelerated by increasing the ionic strength in the SWNT solution. However, SWNT/SWNT multilayers are much more inert to the effect of added electrolyte. In SWNT/SWNT multilayers, the adsorption results in the deposition of 1-3 theoretical nanotube monolayers per adsorbed layer, whereas the nominal SWNT layer thickness is 2-3 times higher in SWNT/polyelectrolyte films prepared with added electrolyte. AFM images show that the multilayers contain a random network of nanotube bundles lying on the surface. Flexible polyelectrolytes (e.g., PDADMA, PSS) probably surround the nanotubes and bind them together. On macroscopic scale, the surface roughness of the multilayers depends on the components and increases with the film thickness.

Journal Article↗

PubMed2006

Molecular layer-by-layer self-assembly of water-soluble perylene diimides through pi-pi and electrostatic interactions.

A layer-by-layer deposition process has been carried out for two oppositely charged water-soluble perylene diimide dyes without the use of intervening polyelectrolyte layers. The strong pi-pi interactions between the perylene moieties help stabilize the layers and simultaneously diminish the fluorescence quantum yield of the array without strongly affecting the absorption or fluorescence spectra. There is an alternation of fluorescence intensity according to which perylene species is on the outer layer, which is interpreted as the effect of facile energy transfer between the perylenes.

Journal Article↗

PubMed2001

Two relatively distinct patterns of ameloblastoma: an anti-apoptotic proliferating site in the outer layer (periphery) and a pro-apoptotic differentiating site in the inner layer (centre).

AIMS: This study was performed to determine the apoptotic behaviour of ameloblastomas by analysing the role of bcl-2 family proteins in ameloblastomas and the location of terminally apoptotic cells in the ameloblastoma epithelial tissues. METHODS AND RESULTS: For immunohistochemistry, tissue sections of 32 patients were treated with an antigen-retrieval METHOD: Primary antibodies against the apoptosis-related proteins, bcl-2, bcl-X, bax, and bak were applied. Besides immunohistochemistry, Western blotting and TUNEL were also performed. Most of the outer layer cells were predominantly stained by the bcl-2 antibody, while most of the inner layer cells were stained by antibodies against the apoptosis-modulating proteins, bax and bak. Among the bcl-2 family, bcl-2 was the most ubiquitously expressed protein in ameloblastomas, while bcl-X was expressed in the greatest concentrations. The major bcl-X protein was bcl-XL. Some of the inner layer cells entered the terminal apoptotic stage, which were revealed by TUNEL. The acanthomatous areas over-expressed the apoptosis-modulating proteins, especially bak. CONCLUSIONS: Ameloblastoma has much more apoptosis-inhibiting protein than the apoptosis-modulating protein. Ameloblastoma has two relatively distinct patterns, an anti-apoptotic proliferating site in the outer layer (periphery) and a pro-apoptotic differentiating site in the inner layer (centre). The acanthomatous area, which was stained strongly by bak antibody and contained numerous terminally apoptotic cells, was considered as the differentiated area.

Adolescent↗

PubMed2002

The impact of a single-layer or double-layer closure on uterine rupture.

OBJECTIVE: Our purpose was to measure the impact of a single-layer or double-layer closure on uterine rupture at subsequent delivery. STUDY DESIGN: This is an observational cohort study of all women undergoing a trial of labor from 1988 to 2000 in a tertiary care center, after a single low transverse cesarean delivery. Factors most highly associated with uterine rupture were identified by using univariate regression analysis. Multivariate logistic regression analysis was used to adjust for selected confounding variables. RESULTS: Of the 2142 women who met the study criteria, 1980 (92.4%) had maternal records and original operative reports reviewed. After adjustments were made for confounding variables, the odds ratio for uterine rupture in women with a single-layer closure was 3.95 (95% CI, 1.35-11.49). CONCLUSION: A single-layer closure of the previous lower segment incision was the most influential factor and was associated with a 4-fold increase in the risk of uterine rupture compared with a double-layer closure.

Cohort Studies↗

PubMed2003

Morphometric analysis of the columnar innervation domain of neurons connecting layer 4 and layer 2/3 of juvenile rat barrel cortex.

We have investigated the dendritic and axonal morphology of connected pairs of L4 spiny neurons and L2/3 pyramidal cells in rat barrel cortex. The 'projection' field of the axons of L4 spiny neurons in layers 2/3, 4 and 5 has a width of 400-500 microm thereby defining an anatomical barrel-column. In layer 2/3, the averaged axonal 'projection' field of L4 spiny neurons together with the dendritic 'receptive' field of the connected L2/3 pyramidal cells form a mostly column-restricted anatomical L4-to-L2/3 'innervation domain' that extends 300-400 microm and includes mostly basal dendrites. In the L4-to-L2/3 innervation domain a single L4 spiny neuron contacts approximately 300-400 pyramidal cells while in the L4-to-L4 innervation domain it contacts approximately 200 other L4 spiny neurons. Similarly approximately 300-400 L4 spiny neurons converge onto a single pyramidal cell and approximately 200 L4 spiny neurons innervate another L4 spiny neuron. The L2/3 pyramidal cell axon has a vertical projection field spanning all cortical layers, and a long-range horizontal field in layers 2/3 (width 1,100-1,200 microm) and 5 (700-800 microm) projecting across column borders. The results suggest that the flow of excitation within a barrel-column is determined by the largely columnar confinement of the L4-to-L4 and L4-to-L2/3 innervation domains. A whisker deflection activates approximately 140 L4 spiny neurons that will generate EPSPs in most barrel-related L2/3 pyramidal cells of a principal whisker column. The translaminar synaptic transmission to layer 2/3 and the axonal projection fields of L2/3 pyramidal cells are the major determinants of the dynamic, multi-columnar map in which a single whisker deflection is represented in the cortex.

Age Factors↗

PubMed1999

Layer-by-layer crystallization and the role of fluctuations in free standing smectic films.

Specular x-ray reflectivity has been used to study the changes in the thermal fluctuation behavior of eight layer freely suspended N-(4-n-butoxybenzilidene)-4-n-octylaniline (4O.8) films during the process of successive layer-by-layer crystallizations. Each of these steps is preceded by the formation of an intermediate layer structure with in-plane hexatic ordering. We find an unusually large reduction of the fluctuations after the emergence of only the first hexatic toplayer. The fluctuation profiles over the film are in all cases quenched at the surfaces though less so after each crystallization step. This behavior supports theoretical arguments that hexatic order is reduced by out-of-plane smectic layer fluctuations.

Journal Article↗

PubMed1991

Skeletal muscle powered ventricle: comparison of double-layered small ventricle and single-layered large ventricle.

Canine left latissimus dorsi (LD) muscles were used to construct two kinds of skeletal muscle powered ventricles (SMPV): a double layered small size (10-17 mL) SMPV (A), and a single-layered large size (40-70 mL) SMPV (B). The same muscle was used sequentially for the construction of both SMPV. A mock circulation system was used for testing. This allowed for change of the preload (10-60 mmHg) and afterload (40-160 mmHg) independently. The peak developed pressure (PDP) and stroke volume (SV) were measured, and the stroke work (SW) was analyzed on line by a computer. The isovolumic PDP was 93.3 +/- 11.8 mmHg at 10 mmHg preload, and 157.7 +/- 20.2 mmHg at 60 mmHg for A, and 37.8 +/- 5.5 mHg and 107.8 +/- 8.5 mmHg for B. The SV and SW at 50 mmHg preload and 80 mmHg afterload were 18.30 +/- 1.25 mL and 1.06 +/- 0.10 x 10(6) erg for A, and 34.18 +/- 2.36 mL and 2.51 +/- 0.28 x 10(6) erg for B. The SV and SW at 20 mmHg preload and 160 mmHg afterload were 2.65 +/- 0.31 mL and 0.27 +/- 0.05 x 10(6) erg for A, and 1.03 +/- 0.23 mL and 0.04 +/- 0.01 x 10(6) erg for (B). The SW generated by the large single-layered SMPV is similar to that reported for the canine left ventricle but requires a high preload. The large single-layered SMPV showed a higher dependence on pre- and afterload changes than the double layered small SMPV, which generates a higher pressure even at low preloads.

Animals↗

PubMed2003

The selection of layer thicknesses to control acoustic radiation force profiles in layered resonators.

Ultrasonic standing waves can be used to generate radiation forces on particles within a fluid. A number of authors have derived detailed representations of these forces but these are most commonly applied using an approximation to the energy distribution based upon an idealized standing wave within a mode based upon rigid boundaries. An electro-acoustic model of the acoustic energy distribution within a standing wave with arbitrary thickness boundaries has been expanded to model the radiation force on an example particle within the acoustic field. This is used to examine the force profile on a particle at resonances other than those predicted with rigid boundaries, and with pressure nodes at different positions. A simple analytical method for predicting modal conditions for combinations of frequencies and layer thickness characteristics is presented, which predicts that resonances can exist that will produce a pressure node at arbitrary positions in the fluid layer of such a system. This can be used to design resonators that will drive particles to positions other than the center of the fluid layer, including the fluid/solid boundary of the layer, with significant potential applications in sensing systems. Further, the model also predicts conditions for multiple subwavelength resonances within the fluid layer of a single resonator, each resonance having different nodal planes for particle concentration.

Journal Article↗

PubMed1996

slpM, a gene coding for an "S-layer-like array" overexpressed in S-layer mutants of Thermus thermophilus HB8.

S-layer deletion mutants of Thermus thermophilus HB8 overproduce a regular array which surrounds groups of several cells. Averages of two-dimensional projections revealed a detailed architecture similar in general morphology and unit cell dimensions to that of the S-layer but having a different mass distribution. The structural components of these "S-layer-like arrays" are a group of three proteins of 52 (P52), 50 (P50), and 36 (P36) kDa, which are overexpressed in S-layer mutants. These three proteins specifically bind antibodies against P52, suggesting that the smaller proteins correspond to fragments derived from P52. This hypothesis was demonstrated by the identity of the trypsin digestion products of P52 and P50. The gene slpM, responsible for the synthesis of P52, was cloned by using synthetic oligonucleotides designed from partial amino acid sequences of P52 and P50. When slpM was expressed in Escherichia coli, proteins specifically recognized by anti-P52 antiserum whose electrophoretic mobilities were similar to those of P52 and P36 were detected. The sequence of slpM revealed the existence of an open reading frame in which the amino termini of P52, P50, and P36 were identified. The unprocessed product of slpM is a 469-amino-acid-long polypeptide whose theoretical M(r) (52,131) was in good agreement with the electrophoretic mobility of P52. The properties deduced for the product of slpM are very different from those of any S-layer protein so far sequenced. The possible roles of SlpM in wild-type cells are discussed.

Amino Acid Sequence↗

PubMed2001

Electric field directed layer-by-layer assembly of highly fluorescent CdTe nanoparticles.

An electric field directed layer-by-layer assembly technique has been developed by combining electrophoretic deposition and the layer-by-layer self-assembly method. This technique is employed to realize spatially selective deposition of CdTe nanoparticles on electrodes of indium-tin oxide (ITO). The fluorescence measurements prove that the selectivity of the film deposition increases against applied voltage and reaches 99% when the voltage is 1.4 V. Upon further increase of the voltage, the selectivity slightly decreases. This decrease occurs because high voltage leads to a degradation of CdTe particles and thus reduces fluorescence intensity of the resultant CdTe film. However, fluorescence investigation indicates that a spacer layer of polyelectrolyte complex between the ITO electrode and the CdTe film is useful to protect the CdTe from being destroyed under high voltages.

Ammonium Chloride↗

PubMed2005

Layer-by-Layer assembly of TiO2 nanoparticles for stable hydrophilic biocompatible coatings.

Stable, super-hydrophilic (water contact angle approximately equal to 0 degrees) titanium dioxide nanoparticle thin films have been obtained on substrates with different initial wettability such as glass, poly(methyl methacrylate) and poly(dimethyl siloxane) using layer-by-layer nano-assembly method. Titanium dioxide nanoparticles were alternated with poly(styrene sulfonate) to form films of thickness ranging from 11 nm to 220 nm. The hydrophilicity of these thin films increases with increasing number of deposited PSS/TiO2 bilayers. It was found that 2, 5 and 20 layers were needed to form super-hydrophilic TiO2 coating on glass, PMMA and PDMS respectively. Oxygen plasma treatment of substrate surfaces enhanced the formation of homogeneous TiO2 films and accelerated the formation of hydrophilic layers. Super-hydrophilicity has been shown to be unique to PSS/TiO2 films as compared with other polyelectrolyte/nanoparticle layers, and UV irradiation may restore hydrophilicity even after months of storing of the samples. Biocompatibility of TiO2 nanoparticle films has been demonstrated by the successful cell culture of human dermal fibroblast.

Biocompatible Materials↗

PubMed2000

Analytical modelling of the elastomeric layer in soft layer hip replacements.

A mechanical analysis is carried out for a flat deformable layer, firmly anchored to a rigid substrate, and frictionlessly compressed by a rigid spherical indenter, with reference to the design of hip replacements whose cup is covered by an elastomeric layer. An available perturbation solution of differential character, developed for a layer subject to plane strain conditions, indented by a cylinder approximated as parabolic in shape and valid for high contact widths, is here extended to the axisymmetric problem of a layer compressed by a paraboloidal indenter. In addition to the paraboloidal idealization, an accurate mathematical description of the indenter spherical profile is incorporated into the modelling of this contact problem. Perturbed solutions up to the second order are developed for both compressible and incompressible layers. Selected numerical examples addressing actual joint geometries are included to assess the validity of the proposed analytical modelling, to explore the accuracy in describing the spherical profile and to compare the contact pressure profiles activated by paraboloidal and spherical indenters.

Biocompatible Materials↗

PubMedDate not supplied

Salmonella enterica serotype enteritidis in table egg layer house environments and in mice in U.S. layer houses and associated risk factors.

Prevalence was estimated for Salmonella enterica serotype eneritidis (SE) in layer house environments (n = 200 layer houses) and house mice (n = 129 layer houses) in 15 states throughout the United States. Environmental swabs were collected from manure, egg belts, elevators, and walkways. Live-catch rodent traps were placed for 4-7 days. Swabs and house mice were submitted to the laboratory for bacterial culture. Overall, 7.1% of layer houses and 3.7% of mice were culture positive for SE. The highest prevalence was in the Great Lakes region of the United States, and no SE was recovered from houses or mice in the southeast region. Presence of SE in layer houses was associated with age/molting, floor reared pullets, and number of rodents trapped. Cleaning and disinfecting houses between flocks was associated with a reduced risk. The prevalence of SE in mice from environmentally positive houses was nearly four times that of mice from environmentally negative houses.

Animal Husbandry↗