Electrochemical and electrogenerated chemiluminescence of clay nanoparticles/Ru(bpy)(3)(2+) multilayer films on ITO electrodes

The electrochemical and electrogenerated chemiluminescence of Ru(bpy)(3)(2+) immobilized in {clay/Ru(bpy)(3)(2+)}(n) multilayer films by layer-by-layer assembly were investigated. The stable multilayer films of clay and Ru(bpy)(3)(2+) were assembled by alternate adsorption of negatively charged clay platelets and positively charged Ru(bpy)(3)(2+) from their aqueous dispersions. UV-vis spectroscopy, quartz crystal microbalance (QCM), cyclic voltammetry, and electrogenerated chemiluminescence (ECL) were used to monitor the immobilization of Ru( bpy)(3)(2+) and the regular growth of the {clay/Ru( bpy)(3)(2+)}(n) multilayer films. The multilayer films modified electrode was used for the ECL detection of tripropylamine ( TPA) and oxalate. The proposed novel immobilized method exhibited good stability, reproducibility and high sensitivity for the determination of TPA and oxalate, which mainly resulted from the contributing of clay nanoparticles with appreciable surface area, special structural features and unusual intercalation properties.

Fabrication and characterization of DNA/QPVP-Os redox-active multilayer film

Calf thymus DNA was immobilized on functionalized glassy carbon, gold and quartz substrates, respectively, by the layer-by-layer (LBL) assembly method with a polycation QPVP-Os, a quaternized poly(4-vinylpyridine) partially complexed with osmium bis(2,2'-bipyridine) as counterions. UV-visible absorption and surface plasmon resonance spectroscopy (SPR) showed that the resulting film was uniform with the average thickness 3.4 nm for one bilayer. Cyclic voltammetry (CV) showed that the total surface coverage of the polycations increases as each QPVP-Os/DNA bilayer added to the electrode surface, but the surface formal potential of Os-centered redox reaction shifts negatively, which is mainly attributed to the intercalation of redox-active complex to DNA chain. The electron transfer kinetics of electroactive QPVP-Os in the multilayer film was investigated by electrochemical impedance experiment for the first time. The permeability of Fe(CN)(6)(3-) in the solution into the multilayer film depends on the number of bilayers in the film. It is worth noting that when the multilayer film is up to 4 bilayers, the CV curves of the multilayer films display the typical characteristic of a microelectrode array.

Effects R3+ on the photoluminescent properties of Ca2R8(SiO4)(6)O-2 : A (R = Y, La, Gd; A= Eu3+, Tb3+) phosphor films prepared by the sol-gel process

Using CaCO3, metal oxides (all dissolved by nitric acid) and tetraethoxysilane Si(OC2H5)(4) (TEOS) as the main starting materials, Ca2R8(SiO4)(6)O-2:A (R = Y, La, Gd; A = EU3+, Tb3+) phosphor films have been dip-coated on quartz glass substrates through the sol-gel process. X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM) and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the 1000 degreesC annealed films are isomorphous and crystallize with the silicate oxyapatite structure. AFM and SEM studies revealed that the phosphor films consisted of homogeneous particles ranging from 30 to 90 nm, with an average thickness of 1.30 mum. The Eu3+ and Tb3+ show similar spectral properties independent of R 3, in the films due to their isomorphous crystal structures. However, both the emission intensity and lifetimes of Eu3+ and Tb3+ in Ca2R8(SiO4)(6)O-2 (R = Y, La, Gd) films decrease in the sequence of R = Gd > R = Y > R = La, which have been explained in accordance with the crystal structures.

Luminescent sol-gel thin films based on europium-substituted heteropolytungstates

Polyester thin films containing europium-substituted heteropolytungstate were obtained on quartz plate by the sol-gel method. The films exhibited the characteristic emission bands of the europium ion. The red to orange intensity ratio (R:O) of Eu3+ in the films increased as compared to the corresponding heteropolytungstate solids. The fluorescence lifetime of europium is shorter in the thin film than in the heteropolytungstate solid. The results indicated that the formation of europium-substituted heteropolytungstate/polyester thin film has great effect on the luminescence of europium- substituted heteropolytungstate.

Preparation and the investigation of its electrochemical and photoluminescent characteristics of organic-inorganic hybrid multilayers containing europium-substituted heteropolytung state

Photoluminescent multilayers were fabricated by layer-by-layer deposition between europium-substituted heteropolytungstate K-13 [Eu(SiW11O39)(2)].28H(2)O (denoted ESW) and a cationic polymer of quaternized poly(4-vinylpyridine) partially complexed with osmium bis(2,2'-bipyridine) (denoted as QPVP-Os) on glassy carbon and quartz substrates. The resulting photoluminescent organic-inorganic hybrid multilayers were characterized by electrochemical impedance spectroscopy, UV-Vis absorption spectrometry, cyclic voltammetry and photoluminescence spectra. Electrochemical impedance spectroscopy, UV-Vis absorption spectrometry and cyclic voltammetry results demonstrated that the multilayers were regular growth each layer adsorption. The photoluminescent properties of the films at room temperature were investigated to show the characteristic Eu3+ emission pattern of D-5(0) --> (7) F-j.

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.

Self-assembling process of alkanethiol monolayers on gold surface via underpotential deposition

It was demonstrated feasible that underpotential deposition(UPD) of copper on a monolayer-modified gold substrate can be used to determine the gold electrode area. The deposition and stripping of a Cu adlayer can take Place reversibly and stably at a bared or a self-assembled monolayer modified gold electrode. The growth kinetics of decanethiol/Au was also investigated via Cu UPD. The difference between the assembling kinetics determined by UPD and that by quartz crystal microbalance measurements reveals the configuration transmutation of the assembled molecules from a disordered arrangement to an ordered arrangement during the self-assembling processes.

Growth of cationic lipid toward bilayer, lipid membrane by solution spreading: scanning probe microscopy study

The growth of cationic lipid dioctadecyldimethylammonium bromide (DODAB) toward bilayer lipid membrane (BLM) by solution spreading on cleaved mica surface was studied by atomic force microscopy (AFM). Bilayer of DODAB was formed by exposing mica to a solution of DODAB in chloroform and subsequently immersing into potassium chloride solution for film developing. AFM studies showed that at the initial stage of the growth, the adsorbed molecules exhibited the small fractal-like aggregates. These aggregates grew up and expanded laterally into larger patches with time and experienced from monolayer to bilayer, finally a close-packed bilayer film (5.4 +/- 0.2 nm) was approached. AFM results of the film growth process indicated a growth mechanism of nucleation, growth and coalescence of dense submonolayer, it revealed the direct information about the film morphology and confirmed that solution spreading was an effective technique to prepare a cationic bilayer in a short time.

Sol-gel fabrication, patterning and photoluminescent properties of LaPO4 : Ce3+, Tb3+ nanocrystalline thin films

Ce3+ and/or Tb3+-doped LaPO4 nanocrystalline thin films and their patterning were fabricated by a sol-gel process combined with soft lithography on silicon and quartz glass substrates. The results of XRD indicated that the films began to crystallize at 700 degreesC. The 1000 degreesC annealed single layer films are transparent by eyes, uniform and crack-free with a thickness of about 200 nm and an average grain size of 100 nm. Patterned thin film with different band widths (5-50 mum) were obtained by micro-molding in capillaries technique. The luminescence and energy transfer properties of Ce3+ and Tb3+ were studied in LaPO4 films.

Synthesis, characterization and fabrication on a glassy carbon electrode of a tetra-iron substituted sandwich-type pentadecatungstodiarsenate heteropolyanion

A novel sandwich-type compound, Na-12[Fe-4(H2O)(2)(As2W15O56)2].41H(2)O, has been synthesized. The compound was well-characterized by means of IR, UV-vis, W-183 NMR and elemental analyses. The compound crystallizes in the triclinic, P (1) over bar symmetry group. The structure of the compound is similar to that of Na-16[M-4(H2O)(2)(As2W15O56)(2)].nH(2)O (M = Cu, Zn, Co, Ni, Mn, Cd), and consists of an oxo-aqua tetranuclear iron core, [(Fe4O14)-O-III(H2O)(2)], sandwiched by two trivacant alpha-Wells-Dawson structural moieties, alpha-[As2W15O56]. Redoxelectrochemistry of the compound has been studied in buffer solutions at pH = 4.7 using polarography and cyclic voltammetry ( CV). The compound exhibited four one-electron couples associated with the Fe(III) center followed by three four-electron redox processes attributed to the tungsten-oxo framework. The compound-containing monolayer and multilayer films have been fabricated on a 4-aminobenzoic acid modified glassy carbon electrode surface by alternating deposition with a quaternized poly(4-vinylpyridine) partially complexed with [Os(bpy)(2)Cl](2+/-). CV, X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy and atomic force microscopy (AFM) have been used to characterize the multilayer films.

Chitosan mediated assembly of gold nanoparticles multilayer

We initiate a systematic exploration of a natural polymer, chitosan, as a structural material for designing functional layers on electrode surfaces in this work. Au colloid films are organized on chitosan layer by adsorption. We have successfully constructed a multilayer An nanoparticle assembly through electrostatic interactions on chitosan functionalized quartz substrates by the alternate treatment of the substrate with solution of citrate-stabilized gold nanoparticles (negatively charged) and chitosan solution (positively charged). The resulting substrates were characterized by UV-Vis spectrometry, atomic force microscopy (AFM), and electrochemical impedance spectroscopy (EIS) measurements. These assemblies of colloid An multilayer are highly stable, and can be kept for a long time in distilled water, only being removed by scratching or extreme electrochemical conditions.

Luminescence properties of rare earth-polyoxometalate thin film deposited by sol-gel process

The rare earth (Eu3+, Dy3+)-polyoxometalate thin films were fabricated on quartz plate by the sol-gel method. The thin films were demonstrated by the luminescence spectra. The thin films exhibit the characteristic emission bands of the rare-earth ions. It is noticed that the yellow to blue intensity ratio (Y:B) of Dy3+ and the red to orange ratio (R:O) of Eu3+ in the films are different from that of the corresponding solids. Furthermore, the thin films present shorter fluorescence lifetime than the pure complexes. The reasons that were responsible for these results were also discussed.

Sol-gel derived silicate oxyapatite phosphor films doped with rare earth ions

Rare-earth (Eu3+, Tb3+)-doped Ca2Y8(SiO4)(6)O-2 luminescent thin films were dip-coated on silicon and quartz glass substrates through a sol-gel route. X-ray diffraction (XRD), scanning electron microscopy (SEM) and luminescence excitation and emission spectra as well as luminescence decays were used to characterize the resultant films. The results of XRD reveal that these films remain amorphous below 700 degreesC, begin to crystallize at 800 degreesC, and crystallize completely around 1000 degreesC with an oxyapatite structure. The grain structure of the film can be seen clearly from SEM micrographs, where particles with various shape and average size of 250 nm can be resolved. The Eu3+ and Tb3+ ions show their characteristic red (D-5(0)-F-7(2)) and green (D-5(4)-F-7(5)) emission in the films with a quenching concentration of 10 and 6 mol% (of Y3+), respectively. The lifetime of Eu-3divided by increases with the heat treatment temperature front 700 to 1100 degreesC.

Study on highly ordered luminescent Langmuir-Blodgett films of heteropolytung state complexes containing lanthanide

Luminescent thin films of heteropolytungstate complexes containing lanthanide (europium or samarium) were successfully fabricated by the Langmuir-Blodgett (LB) technique. The pressure-area isotherm of the monolayer of dimethyldioctadecylammonium. bromide (DODA) is modified rather markedly when the subphase contains the complex of Na9EuW10O36 or Na9SmW10O36. The above results indicate that the monolayer of DODA has a strong interaction with the polyanions of EuW10O369-. (or SmW10O369-). X-ray photoelectron spectra and fluorescent spectra verify that europium and tungsten atoms are 36 36 incorporated into the LB films. Ultraviolet (UV), fluorescent spectra and low-angle X-ray diffraction experiments demonstrate that these LB films have a well-defined lamellar structure. The LB film containing EuW10O369- can give off strong fluorescence 16 on UV irradiation. The characteristic emission behaviors of europium ions in LB films and in the powder of Na9EuW10O369- are discussed. It is found that the intensity ratio of the D-5(0)-F-7(2) transition to the D-5(0)-->F-7(1) transition in LB film is quite different from that in the powder of Na9EuW10O36. The difference of the ratio indicates that the site symmetry of europiurn is distorted in LB film, which is probably due to the strong electrostatic interactions between DODA and polyanions.

Formation of a supported hybrid bilayer membrane on gold: A sterically enhanced hydrophobic effect

Adsorption of a monolayer of didecanoyl-L-alpha-phosphatidylcholine (DDPC) from dispersions of small unilamellar vesicles onto hydrophobic surfaces was investigated by mean of cyclic voltammetry and impedance spectroscopy. The hydrophobic surfaces were self-assembled monolayers of 2-mereapto-3-n-octylthiophene (MOT) on gold. One characteristic of the MOT monolayer is its permeability to organic molecules in aqueous solution, thus providing a more energetically favorable hydrophobic surface for the addition of phospholipid vesicles. The kinetics of the lipid monolayer formation were followed by measuring the time-dependent interfacial capacitance. Unusual values of thickness and capacitance of the MOT/ DDPC bilayers were observed. An interdigitating conformation of the bilayer structure was proposed to interpret the experimental results, The horseradish peroxidase reconstituted into the bilayer demonstrated the expected protein activity, showing practical use in research and in biosensor application.