Counterion exchange at the surface of polyelectrolyte multilayer film for wettability modulation

Counterions present at the surface of polyelectrolyte multilayers (PEMs) were utilized for modulation of surface wettability via ion exchange. The PEM film was dipped in aqueous solutions of different anions, respectively, and the water contact angle of the surface varied from about 10 degrees to 120 degrees, depending on the hydration characteristics of the anion. The ion exchange mechanism was verified by X-ray photoelectron spectroscopy. The process was rapid and reversible. Ionic strength of the polyelectrolyte solution used for preparing the PEMs was found to be crucial to the surface wetting properties and the reversibility and kinetics of the process, and the effects were correlated to the surface density of the excess charge and counterion. This work provides a general, facile and rapid approach of surface property modulation.

Electrodissolution of Inorganic ions/DNA Multilayer Film for Tunable DNA Release

A layer-by-layer film composed of DNA and inorganic zirconium ion (Zr4+) was fabricated on the surface of gold thin film, and an electric field triggered disintegration of the multilayer film was studied by using electrochemical surface plasmon resonance (EC-SPR). EC-SPR results demonstrated that the film was disassembled upon the application of an electric field and the disassembly rate varied with the applied potential, leading to the controlled release of DNA. The electrodissolution could be switched off by removing the electric potential and reactivated by reapplying the potential.

Incorporation of Nanoparticles into Polyelectrolyte Multilayers via Counterion Exchange and in situ Reduction

We report a general method for incorporation of nanoparticles into polyelectrolyte multilayer (PEM) thin films by utilizing the excess charges and associated counterions present in the PEMs. Silver ions were introduced directly into multilayers assembled from poly(diallyldimethylammonium chloride) (PDDA) and poly(styrene sulfonate) (PSS), (PDDA/PSS)(n), by a rapid ion exchange process, which were then converted into silver nanoparticles via in situ reduction to create composite thin films. The size and the content of the nanoparticles in the film call be tuned by adjusting the ionic strength in the polyelectrolyte solutions used for the assembly. Spatial control over the distribution of the nanoparticles in the PEM was achieved via the use of multilayer heterostructure containing PDDA/PSS bilayer blocks assembled at different salt concentrations. Because excess charges and counterions are always present in any PEM, this approach can be applied to fabricate a wide variety of composite thin Films based on electrostatic self-assembly.

Counterions in polyelectrolyte multilayers: A vehicle for introducing functionalities

Counterions present at the surface of polyelectrolyte multilayers were utilized for the introduction of charged species into the multilayer via ion exchange. A typical polyelectrolyte multilayer film with Na+ counterions in the outermost layer was immersed in an AgNO3 aqueous solution and the rapid ion-exchange process was complete within 1 min. The silver ions thus introduced were then reduced in situ and silver nanoparticles were produced at the surface of the multilayer assembly. This example demonstrates that the counterions naturally occurring in every polyelectrolyte multilayer film can be a convenient vehicle for the introduction of various functionalities to the film.

In situ controllable synthesis of polyoxometalate nanoparticles in polyelectrolyte multilayers

Size-controlled Ag3PW12O40 nanoparticles have been synthesized in situ in polyelectrolyte multilayer thin films via layer-by-layer self-assembly.

Construction of hollow DNA/PLL microcapsule as a dual carrier for controlled delivery of DNA and drug

DNA/poly-L-lysine (PLL) capsules were constructed through a layer-by-layer (LbL) self-assembly of DNA and PLL on CaCO3 microparticles, and then used as dual carriers for DNA and drug after dissolution of carbonate cores. The permeability of DNA/PLL microcapsules was investigated with fluorescence probes with different molecular weights by confocal microscopy. The result revealed that the fluorescence probes were able to penetrate the capsule walls even its molecular weight up to 150 kDa. The resultant capsules were used to load drug model molecules-fluorescein isothiocyanate (FITC)-dextran (4 kDa) via spontaneous deposition mechanism.

Hollow DNA/PLL microcapsules with tunable degradation property as efficient dual drug delivery vehicles by alpha-chymotrypsin degradation

Hollow deoxyribonucleic acid (DNA)/poly-L-lysine (PLL) capsules were successfully fabricated through a layer-by-layer (LbL) self-assembly of DNA and PLL on porous CaCO3 microparticles, followed by removal of templates with ethylenediamine tetraacetic acid disodium salt (EDTA). The enzymatic degradation of the capsules in the presence of alpha-chymotrypsin was explored. The higher the enzyme concentration, the higher is the degradation rate of hollow capsules. in addition, glutaric dialdehyde (GA) cross-linking was found to be another way to manipulate degradation rate of hollow capsules.

Layer-by-Layer Buildup of Poly(L-glutamic acid)/Chitosan Film for Biologically Active Coating

A new biocompatible film based on chitosan and poly(L-glutamic acid) (CS/PGA), created by alternate deposition of CS and PGA, was investigated. FT-IR spectroscopy, UV-vis spectroscopy and QCM were used to analyze the build-up process. The growth of CS and PGA deposition are both exponential to the deposition steps at first. After about 9 (CS/PGA) depositions, the exponential to linear transition takes place. QCM measurements combined with UV-vis spectra revealed the increase in the multilayer film growth at different pH (4.4, 5.0 and 5.5). The build-up of the multilayer stops after a few depositions at pH = 6.5. A muscle myoblast cell (C2C12) assay showed that (CS/PGA)(n) multilayer films obviously promote C2C12 attachment and growth.

In-situ fabrication of hybrid polyoxometalate nanoparticles composite films

inorganic-organic hybrid nanoparticles multilayer films were fabricated by extending the method of nucleation and growth of particles in polymer assemblies. The polyelectrolyte matrix was constructed by layer-by-layer self-assembly method. Synthesis of polyoxometalate nanoparticles was achieved by alternately dipping the precursor polyelectrolyte matrix into AgNO3 and H4SiW12O40 aqueous solutions. Repeating the above synthesis process, Ag4SiW12O40 nanoparticles with controllable diameters of 20 to 77 nm were synthesized in the multilayer films in-situ. UV-vis absorption spectra indicate that the nanoparticles grew gradually in the synthesis process. Transmission electron microscopy was used to observe the size and morphology of the nanoparticles.

Polyhedral oligomeric silsesquioxane nanocomposite thin films via layer-by-layer electrostatic self-assembly

Fabrication of ultrathin polymer composite films with low dielectric constants has been demonstrated. Octa( aminophenyl) silsesquioxane (OAPS) was synthesized and assembled with poly( acrylic acid) (PAA) and poly( styrene sulfonate) (PSS) via a layer-by-layer electrostatic self-assembly technique to yield nanoporous ultrathin films. The OAPS was soluble in water at pH 3 or lower, and suitable pH conditions for the OAPS/PAA and OAPS/PSS assemblies were determined. The multilayer formation process was studied by contact angle analysis, X-ray photoelectron spectroscopy, atomic force microscopy, quartz crystal microgravimetry, UV-vis spectroscopy, and ellipsometry. The multilayer growth was found to be steady and uniform, and the analysis of the film surface revealed a rough topography due to OAPS aggregates. The incorporation of porous OAPS molecules into the thin films significantly lowered their dielectric constants. The OAPS/PAA multilayer thin film thus prepared exhibited a dielectric constant of 2.06 compared to 2.58 for pure PAA film. The OAPS/PAA multilayer film was heated to effect cross-linking between the OAPS and the PAA layers, and the transformation was verified by reflection-absorption Fourier transform infrared spectroscopy.

Polyamidoamine dendrimers-assisted electrodeposition of gold-platinum bimetallic nanoflowers

Novel Au-Pt bimetallic flower nanostructures fabricated on a polyamidoamine dendrimers-modified surface by electrodeposition are reported. These polyamidoamine dendrimers were stable, and they assisted the formation of Au-Pt bimetallic nanoflowers during the electrodeposition process. These nanoflowers were characterized by field-emitted scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction, and electrochemical methods. FE-SEM images showed that the bimetallic nanoflower included two parts: the "light" and the "pale" part. The two parts consisted of many small bimetallic nanoparticles, which was attributed to the progressive nucleation process. Moreover, the "light" part contained more bimetallic nanoparticles. The morphologies of bimetallic nanoflowers depended on the electrodeposition time and potential and the layer number of assembled dendrimers. The average size of nanoflowers increased with the increase in electrodeposition time. The layer number of assembled dendrimers obviously affected the size and morphologies of the "pale" parts of deposited nanoflowers.

An effective layer-by-layer adsorption and polymerization method to the fabrication of polyoxometalate-polypyrrole nanoparticle ultrathin films

A layer-by-layer (LbL) adsorption and polymerization method was developed for the controllable preparation of polypyrrole (PPy) nanoparticles within ultrathin films. By repetitive adsorption of pyrrole and subsequent polymerization with 12-molybdophosphoric acid, the polyelectrolyte multilayer films containing PPy nanoparticles were fabricated. UV-visible absorption spectrocopy, Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM) and cyclic voltammograras (CVs) were used to characterize the PPy nanoparticles and their multilayer thin films. UV-visible spectra indicate that the growth of PPy nanoparticles was regular and occurred within the polyelectrolyte films. The size of prepared PPy nanoparticles was found by TEM to increase with the increasing of polymerization cycles. The electrochemistry behavior of the multilayer thin films was studied in detail on ITO. The results suggest that the LbL adsorption and polymerization method developed herein provides an effective way to prepare PPy nanoparticles in the polymer matrix.

A sensitive NADH and glucose biosensor tuned by visible light based on thionine bridged carbon nanotubes and gold nanoparticles multilayer

A NADH and glucose biosensor based on thionine cross-linked multiwalled carbon nanotubes (MWNTs) and Au nanoparticles (Au NPs) multilayer functionalized indium-doped tin oxide (ITO) electrode were presented in this paper. The effect of light irradiation on the enhancement of bioelectrocatalytic processes of the biocatalytic systems by the photovoltaic effect was investigated.

Layer-by-layer assembly of biologically inert inorganic ions/DNA multilayer films for tunable DNA release by chelation

In this work, we illustrate a simple chelation-based strategy to trigger DNA release from DNA-incorporated multilayer films, which were fabricated through the layer-by-layer (LbL) assembly of DNA and inorganic zirconium (IV) ion (Zr4+). After being incubated in several kinds of chelator solutions, the DNA multilayer films disassembled and released the incorporated DNA. This was most probably due to the cleavage of coordination/electrostatic interactions between Zr4+ and phosphate groups of DNA. Surface plasmon resonance (SPR), UV-vis spectrometry and atomic force microscopy (AFM) were used to characterize the assembly and the disassembly of the films.

Fabrication and electrochemical characterization of electrostatic assembly of polyelectrolyte-functionalized ionic liquid and Prussian blue ultrathin films

Polyelectrolyte-functionalized ionic liquid (PFIL) and Prussian blue (PB) nanoparticles were used to fabricate ultrathin films on the ITO substrate through electrostatic layer-by-layer assembly method. Multilayer growth was examined by UV-vis spectroscopy and cyclic voltammetry. The resulting ITO/(PFIL/PB)n electrode showed two couples of well-defined redox peaks and good electrocatalytical activity towards the reduction of hydrogen peroxide.