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PubMed2006

Layer-by-layer deposition of bimetallic nanoshells on functionalized polystyrene beads.

Bimetallic nanoshells on functionalized polystyrene beads have been fabricated through a layer-by-layer deposition technique exploiting electrostatic interaction. The synthesis has been achieved through the immobilization and successive reduction of the corresponding precursor ions. It has been shown that the thickness of the shell can be controlled by a number of cyclic depositions of respective metals onto the surface of the polystyrene beads.

Journal Article↗

PubMed2001

Polarity of layer-by-layer deposited polyelectrolyte films as determined by pyrene fluorescence.

The polarity of polyelectrolyte (PE) multilayer films is investigated with pyrene as a polarity-sensitive probe. Multilayer films of poly(styrene sulfonate) (PSS) and various polycations were prepared by the layer-by-layer self-assembly technique. Pyrene (PY) molecules were inserted into the films by exposing the multilayers to pyrene solutions. By this method a homogeneous distribution of pyrene molecules at low concentration within the film was obtained. The ratio of the fluorescence intensities of the first (I) to the third (III) vibronic band (Py-value) of the pyrene emission spectrum is employed here to determine the polarity of the PE films. PSS and poly(allylamine hydrochloride) (PAH) multilayer films yielded a pyrene value close to the solvent polarity of acetone, while multilayers of PSS and poly(diallyldimethylammonium chloride) (PDADMAC) displayed a value higher than the one corresponding to water. The pyrene values of the polyelectrolyte films were independent from the solvent employed for probe dissolving. Although no direct relationship between solvent polarity and dielectric constant (epsilon) is available, an estimate of the static dielectric constant of the films can be provided by comparing the Py-values of the films with those of various solvents. Changes in the humidity conditions of the film environment in a closed cell did not affect the film polarity. However, a drastic and irreversible reduction of polarity could be induced by actively drying the samples by a nitrogen flow.

Journal Article↗

PubMed2002

A novel layer-by-layer approach to immobilization of polymers and nanoclusters.

This paper reports a simple method for the multilayer immobilization of conjugated polymers, gold nanoparticles on solid supports. Poly(phenyenevinylene) functionalized with aldehyde and aminooxy groups was chemoselectively immobilized onto both glass and gold substrates via layer-by-layer deposition. The physical properties of the thin films were characterized by grazing angle IR, TM-AFM, fluorescence, and UV-visible spectroscopy. This methodology was also successfully applied to prepare polymer/gold nanocluster alternating multilayers. The results show that this methodology provides a general route for preparing robust and functionalizable multilayer films on solid substrates with molecular-level thickness control.

Journal Article↗

PubMed2002

Construction of hydrolytically-degradable thin films via layer-by-layer deposition of degradable polyelectrolytes.

Hydrolytically degradable, multilayered films ranging from 10 to 100 nm have been constructed by the layer-by-layer deposition of degradable polycations and oppositely charged polyanions. Polycations play dual roles in these systems, serving as structural components of the film as well as transient elements designed to trigger release; polyanions serve as structural components and as entities to be released or delivered. The films erode in a controlled manner under physiological conditions and are suitable for the incorporation and subsequent controlled release of functional polyanions such as DNA.

Animals↗

PubMed2003

Layer-by-layer self-assembled chitosan/poly(thiophene-3-acetic acid) and organophosphorus hydrolase multilayers.

The aim of this study is to immobilize an enzyme, namely, organophosphorus hydrolase (OPH), and to detect the presence of paraoxon, which is an organophosphorus compound, using the layer-by-layer (LbL) deposition technique. To lift the OPH from the solid substrate, a pair of polyelectrolytes (positively charged chitosan (CS) and negatively charged poly(thiophene-3-acetic acid) (PTAA)) were combined. These species were made charged by altering the pH of the solutions. LbL involved alternate adsorption of the oppositely charged polyions from dilute aqueous solutions onto a hydrophilic quartz slide. This polyion cushion was held together by the electrostatic attraction between CS and PTAA. The growing process was monitored by fluorescence spectroscopy. OPH was then adsorbed onto the five-bilayer CS/PTAA system. This five-bilayer macromolecular structure compared to the solid substrate rendered stability to the enzyme by giving functional integrity in addition to the ability to react with paraoxon solutions. The ultimate goal is to use such a system to detect the presence of organophosphorus compounds with speed and sensitivity using the absorption and fluorescence detection methodologies.

Acetates↗

PubMed2005

Supramolecular layer-by-layer assembly: alternating adsorptions of guest- and host-functionalized molecules and particles using multivalent supramolecular interactions.

The stepwise construction of a novel kind of self-assembled organic/inorganic multilayers based on multivalent supramolecular interactions between guest-functionalized dendrimers and host-modified gold nanoparticles has been developed, yielding supramolecular layer-by-layer assembly. The deposition process was monitored by surface plasmon resonance spectroscopy. Further characterization of the multilayer films was performed by means of UV/vis absorption spectroscopy, which showed a linear increase in absorption with the number of bilayers. The growth of the gold nanoparticle plasmon absorption band corresponded to approximately a dense monolayer of gold nanoparticles per bilayer. Ellipsometry and atomic force microscopy (AFM) scratching experiments were used to measure the development of the film thickness with the number of bilayers, confirming linear growth and a thickness increase of approximately 2 nm/bilayer.

Journal Article↗

PubMed2006

Chemically selective sensing through layer-by-layer incorporation of biorecognition into thin film substrates for surface-enhanced resonance Raman scattering.

In this work, the fabrication, characterization, and application of avidin/Ag nanoparticle layer-by-layer (LbL) films as chemically selective substrates for surface-enhanced resonance Raman scattering (SERRS) is demonstrated. The biospecific interaction between avidin and the small molecule biotin, one of the strongest known to exist in nature, is exploited to preferentially capture biotinylated species from solution. This highly favored adsorption is shown to yield SERRS concentration enhancements and improved detection sensitivities of ca. 102 for commercially available and in situ prepared biotinylated species over their nontagged counterparts.

Avidin↗

PubMed2005

Electrochemical and electrochromic properties of layer-by-layer films from WO(3) and chitosan.

The design of improved materials for electrochromic applications now involves extensive use of novel composites, thus requiring an investigation of the mechanisms responsible for electrochromism in these structures. Using films of WO(3) and chitosan produced with the layer-by-layer (LBL) technique, we demonstrate that characteristics such as the number of electrochemical active sites (K), the molar absorption coefficient (epsilon), and the electrochromic efficiency (eta) can be obtained using the quadratic logistic equation (QLE). The complexation ability between chitosan and WO(3) allowed the growth of visually uniform multilayers of the composite, with the same amount of material adsorbed in each deposition cycle. By fitting the absorbance changes (DeltaA) resulting from the electronic intervalence transfer from W(V) to W(VI) sites in four-bilayer LBL films of WO(3)/chitosan and WO(3)/chitosan with ethanol in the precursor dispersion, K was estimated to be ca. 5.5 x 10(-8) mol cm(-2) and 3.6 x 10(-8) mol cm(-2), respectively. The molar absorption coefficient and electrochromic efficiency vary with the charge injected because of the saturation of W(V) sites and the dissipation and feedback effects implicit in the QLE associated with ion-network interactions, such as the proton trapping effect. The LBL film of WO(3)/chitosan showed a smaller molar absorption coefficient and electrochromic efficiency than that containing ethanol because of a greater proton trapping effect for the LBL film with no ethanol. This enhanced trapping effect was seen as a decrease in the electronic flux involved in intervalence transfer in electrochemical impedance spectroscopy experiments.

Journal Article↗

PubMed2005

Layer-by-layer electrodeposition of copper in the presence of o-phenanthroline, caused by a new type of hidden NDR oscillation with the effective electrode surface area as the key variable.

Electrochemical deposition of copper (Cu) from aqueous acidic Cu2+ solutions with o-phenanthroline (o-phen) shows both potential and current oscillations, together with a (partially hidden) N-shaped negative differential resistance (N-NDR), indicating that the oscillations are classified into hidden N-NDR (or HN-NDR) oscillations. The color and the surface morphology of Cu deposits oscillate in synchronization with the potential and current oscillations. Microscopic inspection has shown that dense round Cu leaflets, which look gray, grow in the positive side of the potential oscillation or in the high-current state of the current oscillation, whereas thin Cu leaflets, which look black, grow in the opposite-side stages of the potential and current oscillations, thus finally resulting in a layered Cu deposit with the layer thickness of about 5 microm. The appearance of the NDR is explained to be due to adsorption of the reduced form of a [Cu(II)(o-phen)2]2+ complex, which suppresses the Cu electrodeposition. The increase in the effective electrode surface area by growth of thin Cu leaflets, on the other hand, causes a current increase that can hide the NDR. This NDR-hiding mechanism is of a new type and the present oscillation is regarded as a new-type of HN-NDR oscillator.

Copper↗

PubMed2006

Nanopatterning and nanocharge writing in layer-by-layer quinquethiophene/phthalocyanine ultrathin films.

Nanometer-scale patterning and charging in layer-by-layer (LbL) ultrathin films of quinquethiophene (5TN)/phthalocyanine (CuPS) provides a novel write-read device using a standard current-sensing atomic force microscopy (CS-AFM). The AFM height images showed dented or raised morphological features that could be selectively manipulated by changing the direction of the bias voltages. The conductivity was repeatedly changed between a conductive and insulating state, originating from an electrochemical charging-discharging effect. This was attributed to electrochemical ion transport and the residual mobile ions present in LbL films. Finally, the nanocharge pattern was written by CS-AFM and read out in a conductivity map image.

Journal Article↗

PubMed2006

Interaction between myoglobin and hyaluronic acid in their layer-by-layer assembly: quartz crystal microbalance and cyclic voltammetry studies.

Myoglobin (Mb), with different net surface charges at different pH in buffers and negatively charged hyaluronic acid (HA) at pH 5.0 in solutions were alternately adsorbed onto various solid surfaces and successfully assembled into {Mb/HA}(n) layer-by-layer films. The Mb in {Mb/HA}(n) films showed a quasi-reversible cyclic voltammetry (CV) response for its heme Fe(III)/Fe(II) redox couple. Quartz crystal microbalance (QCM) and CV were used to confirm the film growth and characterize the films. The interaction between Mb and HA and the influencing factors for Mb adsorption on HA surface, such as pH, Mb concentration, and ionic strength, were investigated in detail. The assembly driving force for {Mb/HA}(n) films, especially for the films assembled with like-charged Mb and HA, was found to be of electrostatic origin, while the secondary interaction such as hydrophobic interaction also plays an important role in some circumstances. Although the growth of {Mb(pH 7.0)/HA}(n) and {Mb(pH 9.0)/HA}(n) films was linear with the adsorption step, the exponential growth of {Mb(pH 5.0)/HA}(n) films was observed, especially when the films became thick. This exponential increase of mass and thickness with deposition step for {Mb(pH 5.0)/HA}(n) films was most probably attributed to the diffusion mechanism in which some HA molecules could diffuse in to and out of the whole films during the film assembly. Atomic force microscopy (AFM) results supported this speculation. UV-vis and IR spectroscopies of {Mb/HA}(n) films, combined with the comparative CV experiments of {Mb/HA}(n) and {catalase/HA}(n) films, suggest that Mb in the {Mb/HA}(n) multilayer films retains its near-native structure.

Adsorption↗

PubMed2006

Loading behavior of {chitosan/hyaluronic acid}n layer-by-layer assembly films toward myoglobin: an electrochemical study.

When {CS/HA}n layer-by-layer films assembled by oppositely charged chitosan (CS) and hyaluronic acid (HA) were immersed in myoglobin (Mb) solution at pH 5.0, Mb was gradually loaded into the {CS/HA}n films, designated as {CS/HA}n-Mb. The cyclic voltammetric (CV) peak pair of Mb FeIII/FeII redox couple for {CS/HA}n-Mb films on pyrolytic graphite (PG) electrodes was used to investigate the loading behavior of {CS/HA}n films toward Mb. The various influencing factors, such as the number of bilayers (n), the pH of Mb loading solution, and the ionic strength of solution, were investigated by different electrochemical methods and other techniques. The results showed that the main driving force for the bulk loading of Mb was most probably the electrostatic interaction between oppositely charged Mb in solution and HA in the films, while other interactions such as hydrogen bonding and hydrophobic interaction may also play an important role. Other polyelectrolyte multilayer (PEM) films with different components were compared with {CS/HA}n films in permeability and Mb loading, and electroactive probes with different size and surface charge were compared in their incorporation into PEM films. The results suggest that due to the unique structure of CS and HA, {CS/HA}n films with relatively low charge density are packed more loosely and more easily swelled by water, and have better permeability, which may lead to the higher loading amount and shorter loading time for Mb. The protein-loaded PEM films provide a new route to immobilize redox proteins on electrodes and realize the direct electrochemistry of the proteins.

Adsorption↗

PubMed2006

Electro-nanopatterning of surface relief gratings on azobenzene layer-by-layer ultrathin films by current-sensing atomic force microscopy.

The electro-nanopatterning and mechanism of pattern formation in azobenzene-containing layer-by-layer (LbL) ultrathin films is described using surface probe microscopy techniques. First, arrays of nanodots were patterned on these films to investigate applied time at constant voltage bias dependence in electro-nanopatterning. The anisotropic mass transport and polar alignment of the azobenzene-containing films were observed after applying the electric field and heating the sample locally with the cantilever tip. On the basis of this novel phenomenon, small-sized surface relief gratings (SRG)s and their alignment were fabricated and observed by current-sensing atomic force microscopy. The rate of mass transport for the polymer is mainly controlled by the applied time at constant voltage bias between the cantilever and the electrode/substrate.

Letter↗

PubMed2004

Facile tailoring of film morphology and release properties using layer-by-layer assembly of thermoresponsive materials.

Layer-by-layer self-assembly was used to prepare thermoresponsive thin films of poly(N-isopropylacrylamide) (PNIPAAm) and poly(acrylic acid) (PAA) based on hydrogen bonding. The temperature of PNIPAAm adsorption was shown to significantly affect both the mass proportion of PNIPAAm in the film and the film surface morphology. When the adsorption was conducted at temperatures close to the lower critical solubility temperature of PNIPAAm, the amount of PNIPAAm in the film increased significantly (from 51 to 59%), and the total film mass increased by 30-40%. The films prepared at 30 degrees C also exhibited a lower surface roughness (1-2 nm) compared with 5-8 nm when prepared at 10 or 21 degrees C. The resulting multilayer films ([PAA/PNIPAAm]10) were capable of being reversibly loaded and unloaded with dye (Rhodamine B) by exposure to solutions at elevated temperatures. The rate of loading and release was shown to depend on both the solution temperature and film preparation temperature, leading to tunable loading/release properties.

Acrylic Resins↗

PubMed2005

Combining layer-by-layer assembly with electrodeposition of silver aggregates for fabricating superhydrophobic surfaces.

Taking advantage of the stability and penetrability of layer-by-layer (LbL) films, we develop a novel method to fabricate a branchlike structure of Ag aggregates on the matrix of a LbL polyelectrolyte multilayer by an electrodeposition technique. The morphology of Ag aggregates can be adjusted by electrodeposition time and potential. Moreover, after further chemisorption of a self-assembled monolayer of n-dodecanethiol, the as-prepared surface becomes superhydrophobic with a contact angle as high as 154 degrees and a tilt angle lower than 3 degrees.

Journal Article↗

PubMed2005

Sustained release control via photo-cross-linking of polyelectrolyte layer-by-layer hollow capsules.

We describe the formation and permeability of polyelectrolyte multilayer hollow-shell capsules by photo-cross-linking and controlled-release (fluorescence) studies. The hollow shells were prepared by alternate layer-by-layer (LbL) adsorption of photo-cross-linkable benzophenone modified poly(allylamine hydrochloride) and poly(sodium 4-styrenesulfonate) on polystyrene particles, followed by removing the core with tetrahydrofuran. Zeta potential measurements, fourier transform infrared spectroscopy, and transmission electron microscopy were used to verify the LbL process integrity. A model drug, rhodamine B (RB), was successfully loaded into the polyelectrolyte hollow capsules. The release kinetics of RB was investigated using fluorescence spectroscopy. The permeability of RB through the hollow shells was effectively controlled based on UV irradiation time. It was shown that the release of RB molecules can be controlled by the degree of cross-linking induced in the multilayer.

Journal Article↗

PubMed2005

Tunable drug release from hydrolytically degradable layer-by-layer thin films.

The development of new thin film fabrication techniques that allow for precise control of degradation and drug release properties could represent an important advance in the fields of drug delivery and biomedicine. Polyelectrolyte layer-by-layer (LBL) thin films can be assembled with nanometer scale control over spatial architecture and morphology, yet very little work has focused on the deconstruction of these ordered thin films for controlled release applications. In this study, hydrolytically degradable LBL thin films are constructed by alternately depositing a degradable poly(beta-amino ester) (polymer 1) and a series of model therapeutic polysaccharides (heparin, low molecular weight heparin, and chondroitin sulfate). These films exhibit pH-dependent, pseudo-first-order degradation and release behavior. The highly versatile and tunable properties of these materials make them exciting candidates for the controlled release of a wide spectrum of therapeutics.

Journal Article↗

PubMed2005

Layer-by-layer assembly of human serum albumin and phospholipid nanotubes based on a template.

The preparation of nanotubes from human serum albumin (HSA) and mixtures of L-alpha-dimyristoylphosphatidic acid (DMPA)/HSA is described. The nanotubes were prepared via alternate adsorption of HSA of different/opposite charges (by variation of the pH) or by sequential adsorption of DMPA and HSA, respectively, onto the inner surfaces of porous anodic alumina templates. This simple layer-by-layer assembly results in a monodisperse size distribution and a uniform orientation. The nanotubes allow the specific incorporation of lipophilic components such as channels or receptors and may thus serve as probes or sensors for biological systems.

Circular Dichroism↗