Bending of layer-by-layer films driven by an external magnetic field.

We report on optimized architectures containing layer-by-layer (LbL) films of natural rubber latex (NRL), carboxymethyl-chitosan (CMC) and magnetite (Fe3O4) nanoparticles (MNPs) deposited on flexible substrates, which could be easily bent by an external magnetic field. The mechanical response depended on the number of deposited layers and was explained semi-quantitatively with a fully atomistic model, where the LbL film was represented as superposing layers of hexagonal graphene-like atomic arrangements deposited on a stiffer substrate. The bending with no direct current or voltage being applied to a supramolecular structure containing biocompatible and antimicrobial materials represents a proof-of-principle experiment that is promising for tissue engineering applications in biomedicine.

Combinatorial polyelectrolyte multilayer film fabrication.

A combinatorial strategy for the fabrication of a library of polyelectrolyte multilayer films is presented in this paper. This innovative approach involves the parallel formation of polyelectrolyte multilayer films in the individual wells of polystyrene microtitre plates under various deposition conditions. The progress of film formation was monitored via the intensity of the UV-vis absorbance of one of the depositing polyelectrolytes using a conventional microplate reader.

Evaluation of chitosan gel as antibiotic and photosensitizer delivery.

This work suggests the use of chitosan gel imbued with the photosensitizer Photogem and with the antibiotic Tetraclin as a possible drug delivery system. The results reveal a decrease in the photosensitizer level of toxicity. Besides, the interaction between Photogem and chitosan gel causes a red shift in the photosensitizer spectrum, increasing its absorption in the therapeutic window (600-700 nm).

SERS detection of environmental pollutants in humic acid-gold nanoparticle composite materials.

Humic acid (HA) solutions provide an unexpected medium for direct fabrication of gold nanoparticles (HA-AuNP) and a clear window for surface-enhanced Raman scattering (SERS) with many potential applications in the ultrasensitive chemical analysis of environmental pollutants. It is demonstrated that the HA-AuNP fabrication can be easily achieved in a wide range of pH (2 to 12). The background SERS spectra of HA is relatively weak in absolute intensity, allowing the detection of the enhanced Raman signal from trace amount of contaminants.

Probing chitosan and phospholipid interactions using Langmuir and Langmuir-Blodgett films as cell membrane models.

The interaction between chitosan and Langmuir and Langmuir-Blodgett (LB) films of dimyristoyl phosphatidic acid (DMPA) is investigated, with the films serving as simplified cell membrane models. At the air-water interface, chitosan modulates the structural properties of DMPA monolayers, causing expansion and decreasing the monolayer elasticity. As the surface pressure increased, some chitosan molecules remained at the interface, but others were expelled.

Selective surface-enhanced fluorescence and dye aggregation with layer-by-layer film substrates.

One of the avenues for the development of the analytical applications of surface enhanced spectroscopy is the engineering of enhancing substrates that would be selective and target specific. In the present report, the proof of this concept is demonstrated using the layer-by-layer (LbL) technique to fabricate portable selective substrates containing metal nanoparticles which can provide surface enhanced fluorescence (SEF) or surface enhanced Raman scattering (SERS). The selectivity to ionic species is attained by adding metal-free top layers of polymer electrolytes to an LbL SERS enhancing substrate.

Interaction of chitosan with cell membrane models at the air-water interface.

In this paper we employed phospholipid Langmuir monolayers as membrane models to probe interactions with chitosan. Using a combination of surface pressure--area and surface potential--area isotherms and rheological measurements with the pendent drop technique, we observed that chitosan interacts with phospholipid molecules at the air-water interface. We propose a model in which chitosan interacts with the phospholipids mainly through electrostatic interactions, but also including H-bonding and hydrophobic forces, depending on the phospholipid packing density.

The effect of the layer structure on the activity of immobilized enzymes in ultrathin films.

The molecular engineering capability of the layer-by-layer (LbL) method for fabricating thin films has been exploited in order to immobilize glucose oxidase (GOD) in films with alternating layers of chitosan. Chitosan was proven a good scaffolding material, as GOD molecules preserved their catalytic activity towards glucose oxidation. Using electrochemical measurements, we showed that chitosan/GOD LbL films can be used to detect glucose with a limit of detection of 0.

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.

Optical storage and surface-relief gratings in azobenzene-containing nanostructured films.

This paper brings an overview of photoisomerization-derived properties in azobenzene-containing nanostructured films produced with the Langmuir-Blodgett (LB) and layer-by-layer (LbL) methods. Emphasis was placed on the optical storage and formation of surface-relief gratings (SRGs), where the distinctive properties of the nanostructured films were highlighted. For optical storage, in particular, a discussion was made of the higher birefringence induced in LB films from azopolymers due to their organized nature, and of the strong effects from ionic interactions on the photoisomerization of azochromophores in LbL films.

Surface-enhanced raman scattering on dendrimer/metallic nanoparticle layer-by-layer film substrates.

In this paper, the fabrication, characterization, and application of unique layer-by-layer (LBL) films of dendrimers and metallic nanoparticles is reported. Silver nanoparticles (d = approximately 20 nm) are produced in solution by sodium citrate reduction and incorporated into thin films with generation 1 and 5 DAB-Am dendrimers (polypropylenimine dendrimers with amino surface groups) by the LBL technique. The resulting nanocomposite films are characterized by UV-visible surface plasmon absorption and atomic force microscopy (AFM) measurements, and employed as substrates for surface-enhanced Raman scattering (SERS) of 2-naphthalenethiol.

Morphology characterization of layer-by-layer films from PAH/MA-co-DR13: the role of film thickness.

We report on the use of dynamic scale theory and fractal analyses in the study of distinct growth stages of layer-by-layer (LBL) films of poly(allylamine hydrochloride) (PAH) and a side-chain-substituted azobenzene copolymer (Ma-co-DR13). The LBL films were adsorbed on glass substrates and characterized with atomic force microscopy with the Ma-co-DR13 at the top layer. The granular morphology exhibited by the films allowed the observation of the growth process inside and outside the grains.

Particle and surface characterization of a natural illite and study of its copper retention.

Illite clays are known to have a strong affinity for metallic pollutants in the environment and can be applied as low-cost adsorbents for industrial waste treatment. A crucial factor in the development of such applications, however, is the understanding of the chemical, mineralogical, and colloidal properties of these clays. It is also important to understand the mechanisms involved in the surface adsorption of metals by these adsorbants.

Silver nanowire layer-by-layer films as substrates for surface-enhanced Raman scattering.

In this paper, the fabrication of highly stable, surface-enhanced Raman scattering (SERS) active dendrimer/silver nanowire layer-by-layer (LBL) films is reported. Ag nanowires, approximately 100 nm in diameter, were produced in solution and transferred, using the LBL technique, onto a single fifth-generation DAB-Am dendrimer layer on a glass substrate. The Ag nanowires, and the resulting LBL films were characterized using UV-visible surface plasmon absorbance, while the LBL films were further characterized by atomic force microscopy measurements and surface-enhanced Raman and resonance Raman scattering of several analytes.

Gold nanoparticle embedded, self-sustained chitosan films as substrates for surface-enhanced Raman scattering.

In this work, self-sustained, biocompatible, biodegradable films containing gold nanostructures have been fabricated for potential application in nanobioscience and ultrasensitive chemical and biochemical analysis. We report a novel synthesis of gold nanoparticles mediated by the biopolymer chitosan. Self-supporting thin films are formed from the resultant gold-chitosan nanocomposite solutions and characterized by UV-visible surface plasmon absorption, transmission electron microscopy, atomic force microscopy, infrared absorption, and Raman scattering measurements.