Dear Colleagues

182(1-3) (2001), 239-245
A novel strategy to prepare colloidal Au multilayers using 3- (mercaptopropyl)-trimethoxysilane (MPTMS) as a linker molecule was demonstrated. The nanostructure consists of alternate layers of ultrathin thiol-functionalized silica films and Au colloids. In which, a surface sol-gel process was used to prepare the thiol-functionalized silica films. During the self- assembly of Au colloids, a reiterative immersion-rinse approach was used to ensure maximum coverage of isolated Au colloids. The surface coverage of the first colloidal Au monolayer is ca. 45% of a dose-packed monolayer. The method yields uniform layer- by-layer growth colloidal Au multilayers through self-assembly at the Au(lll) planes, as judged by the ultraviolet-visible (UV- vis) spectroscopic data and the X-ray diffraction (XRD) patterns. (C) 2001 Elsevier Science B.V. All rights reserved.

[189] Layered Nanoarchitectures Between Cationic and Anionic Materials - Composite Assemblies of Polyions, Lipid Bilayers, and Proteins

K. Ariga, Y. Sasaki, H. Horiguchi, N. Horiuchi and J. Kikuchi

DEFECT DIFFUS FORUM 191 (2001), 35-59

Many functional molecules such as polyions, proteins, colloidal particles, dyes, and lipid membranes, can be assembled as thin films through layer-by-layer alternate adsorption. This technique is useful for preparing nano-sized enzyme reactors where the enzymes are sandwiched between molecular films of polyions or lipids. In order to systematically compare the enzymatic activity and the related properties between the polyion-protein assemblies and lipid-protein assemblies, in this study, we prepared both kinds of assemblies and examined their enzymatic activity. Two kinds of enzymes, lactate dehydrogenase (LDH) and alcohol dehydrogenase (ADH), were assembled with the polycation, poly(diallyldimethylammonium chloride) (PDDA), and an artificial cationic lipid. The assembling behavior was analyzed by a quartz crystal microbalance (QCM) with nanogram precision which revealed that the polyion, the lipid membrane, and the enzyme layers can be repeatedly and reproducibly assembled. The catalytic activity of the obtained films was spectrophotometrically examined. The activity of the LDH on a lipid-surface film was apparently greater than that of the LDH on a polyion-surface film. This difference might originate from the difference in the surface nature of the films. The Michaelis-Menten analysis suggested that the concentration increase in an anionic substrate in the vicinity of the cationic lipid surface led to the enhanced enzymatic activity. The surface morphology of the film was investigated using atomic force microscopy(AFM). The lipid- surface film apparently has a rough surface, while a relatively smooth surface morphology was observed for the polyion-surface film. This difference in the surface morphology might affect the activity of the immobilized enzymes.

[190] Preparation of Multilayered Nanocomposites of Polyoxometalates and Poly(Amidoamine) Dendrimers

L. Cheng and J. A. Cox

ELECTROCHEM COMMUN 3(6) (2001), 285-289

A layer-by-layer (LBL) deposition technique based on electrostatic attraction of oppositely charged species was used to fabricate multilayer films consisting of polyoxometalates (POMs) (Keggin-structure PMo12O403- or Dawson-structure P2W18O626-) and a generation-4 poly(amidoamine) dendrimer (G4- PAMAM) on quartz treated with poly(diallyldimethylammonium chloride) and gold treated with (aminothiophenol (4-ATP). Both of the UV-visible spectrophotometry and cyclic voltammetry proved a successful formation of uniform and well-defined self- assemblies with multilayered supramolecular structure. With PM0(12)O(40)(3-) each layer contained 4.6 x 10(-11) mol cm(-2). Direct attachment of PMo12O403- yielded a surface excess of 3.6 x 10(-11) mol cm(-1) in that monolayer. The comparison suggested an expansion of the effective surface area by the multicharged macromolecule, G4-PAMAM. The multilayer films mediated the reduction of iodate and of nitrite. (C) 2001 Elsevier Science B.V. All rights reserved.

[191] Shrinking of Ultrathin Polyelectrolyte Multilayer Capsules upon Annealing - A Confocal Laser-Scanning Microscopy and Scanning Force Microscopy Study

S. Leporatti, C. Gao, A. Voigt, E. Donath and H. Möhwald

Eur. Phys. J. E 5(1) (2001), 13-20

Heating-induced morphological changes of micrometer size capsules prepared by step-wise deposition of oppositely charged polyelectrolytes onto melamine formaldehyde (MF) latex particles and biological cells with subsequent dissolution of the core have been investigation by confocal laser scanning microscopy (CLSM) and scanning force microscopy (SFM). For poly(styrenesulfonate-Na salt)/poly(allylamine hydrochloride) polyelectrolyte capsules a remarkable heating-induced shrinking is observed. An increase of the wall thickness corresponding to the capsule diameter decrease is found. The morphology of these microcapsules after temperature treatment is characterized. The thickening of the polyelectrolyte multilayer is interpreted in terms of a configurational entropy increase via polyanion- polycation bond rearrangement.

[192] Elasticity of Hollow Polyelectrolyte Capsules Prepared by the Layer-by-Layer Technique

C. Gao, E. Donath, S. Moya, V. Dudnik and H. Möhwald

Eur. Phys. J. E 5(1) (2001), 21-27

Osmotically induced deformations (invaginations) of polyelectrolyte capsules were observed in poly(styrene sulfonate, sodium salt) (PSS) solution since PSS of Mw 70 000 is excluded from the capsule interior. It was found that there is a critical osmotic pressure difference at which the initial spherical capsule shape becomes unstable and invaginations are formed. This critical osmotic pressure was obtained as a function of the wall thickness and the capsule size. A theoretical model is provided which describes the relationship between the critical osmotic pressure, the elasticity modulus, the capsule wall thickness, and the capsule radius. The model was verified by measuring the invagination onset as a function of particle radius and wall thickness. The elasticity modulus of the PSS/PAH (polyallylamine hydrochloride) polyelectrolyte multilayer was measured as a function of wall thickness and capsule diameter. The modulus ranges between 500 and 750 MPa, which indicates a relatively strongly interconnected polyelectrolyte multilayer structure. With higher molecular weight PAH the elasticity modulus of the PSS/PAH multilayer was slightly enhanced.

[193] Ultrathin Self-Assembled Polyelectrolyte Multilayer Membranes

B. Tieke, F. Vanackern, L. Krasemann and A. Toutianoush

Eur. Phys. J. E 5(1) (2001), 29-39

The paper is concerned with ultrathin membranes prepared upon alternating layer-by-layer adsorption of cationic and anionic polyelectrolytes on a porous substructure. The formation of the polyelectrolyte multilayer membranes is characterised and the transport of gases, liquid mixtures and ions across the membranes is studied. In particular, the use of the membranes of alcohol/water separation under pervaporation conditions, and for the separation of mono- and divalent ions is described. It is demonstrated that upon a suitable choice of polyelectrolytes and substructures, and a careful optimisation of preparation and operation conditions, membranes can be tailored exhibiting an excellent separation capability.

[194] Complexation and Distribution of Counterions in a Grafted Polyelectrolyte Layer

Y. Tran and P. Auroy

Eur. Phys. J. E 5(1) (2001), 65-79

The complexation and the distribution of various cations, bound to a poly(styrene sulfonate) brush, have been investigated using infra-red spectroscopy and neutron reflectivity. Small counterions (like tetremethylammonium) are distributed throughout the brush in such a way that a local electroneutrality is ensured. They also exchange readily with other bulk small cations. On the other hand, model polycations are irreversibly trapped to the brush despite a relative small number of ionic bonds involved in the complexation. These complexed polycations are localized at the outer border of the brush, forming a macromolecular barrier. However, this spatial segregation does not allow the buildup of polyelectrolyte multilayers. Cationic surfactants are associated stoichiometrically with the brush sulfonates but unlike small counterions, this complexation is ''irreversible'' and induces a restructuring of the polymer interface.

[195] Xenotransplantation of Parathyroids in Rats Using Barium- Alginate and Polyacrylic-Acid Multilayer Microcapsules

A. Gaumann, M. Laudes, B. Jacob, R. Pommersheim, C. Laue, W. Vogt and J. Schrezenmeir

EXP TOXICOL PATHOL 53(1) (2001), 35-43

The integrity and function of encapsulated parathyroid tissue following xenotransplantation is limited by oxygen and nutrition supply and capsule fibrosis. Since some of these factors depend on stability and biocompatibility of the coating material, multilayer microcapsules have been developed. Parathyroid tissue pieces and digested single cells from pigs were encapsulated in barium-alginate and in polyacrylic acid (PAA) multilayer capsules. After 7 days of culture the function of the encapsulated cells were assessed. Subsequently, in a part of the cultured microcapsules the viability was directly assessed whereas the other part was transplanted in dark animal [DA] rats for 30 days. After explantation viability and fibrotic reaction were examined. Single cells showed a significant increase in parathyroid hormone [PTH] secretion when exposed to medium low in calcium, whereas minced tissue pieces revealed necrosis without stimulatory responsiveness. Morphometry showed significantly better viability of single cells compared with minced tissue in vitro and in vivo. The fibrotic reaction against capsules with minced tissue was more pronounced than for capsules containing single cells. There was no difference between barium alginate and PAA capsules when containing minced tissue. In single cells, however, the fibrous tissue reaction differed significantly between barium alginate and PAA capsules. Encapsulated single cells of parathyroid tissue maintain detectable function and viability. In contrast minced tissue underwent necrosis and induced significantly more connective tissue reaction than single cells indicating an interrelationship between necrosis and fibrosis.

[196] Polarity of Layer-by-Layer Deposited Polyelectrolyte Films as Determined by Pyrene Fluorescence

C. Tedeschi, H. Möhwald and S. Kirstein

J. Am. Chem. Soc. 123(5) (2001), 954-960

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.

[197] 2 Modes of Linear Layer-by-Layer Growth of Nanoparticle- Polylectrolyte Multilayers and Different Interactions in the Layer-by-Layer Deposition

J. W. Ostrander, A. A. Mamedov and N. A. Kotov

J. Am. Chem. Soc. 123(6) (2001), 1101-1110

The structure of the multilayer assemblies of yttrium iron garnet nanoparticles (YIG) with polyelectrolytes was investigated with the emphasis on the control of the particle density in the adsorption layers. It was found that the growth of YIG films prepared by the layer-by-layer assembly can occur via two deposition modes: (1) sequential adsorption of densely packed adsorption layers (normal growth mode) and (2) in-plane growth of isolated particle domains (lateral expansion mode). Importantly, the dependence of the optical density on the number of deposition cycles remains linear in both cases. Microscopy results indicate that the origin of the lateral growth is in the interplay of particle/particle and particle/ polyelectrolyte interactions rather than in a substrate effect. The lateral expansion mode is a general attribute of the layer- by-layer deposition and can be observed for various aqueous colloids. Fur the preparation of sophisticated multifunctional assemblies on nanoparticles, the film growth via domain expansion should be avoided, and therefore, one must be able to control the growth pattern. The switch from lateral to normal growth mode can be effected by grafting charged organic groups to YIG nanoparticles. Hydrophobic interactions between the hydrocarbon groups of the modified YIG and polyelectrolyte significantly increase the attractive component of the particle/ polyelectrolyte and particle/particle interactions. The films from modified YIG display densely packed nanoparticle layers with a greatly reduced number of defects.

[198] Weak Versus Strong - A Weak Polyacid Embedded Within a Multilayer of Strong Polyelectrolytes

A. F. Xie and S. Granick

J. Am. Chem. Soc. 123(13) (2001), 3175-3176

[199] Efficient Photocurrent Generation in Novel Self-Assembled Multilayers Comprised of (60)Fullerene-Cationic Homooxacalix(X)Arene Inclusion Complex and Anionic Porphyrin Polymer

A. Ikeda, T. Hatano, S. Shinkai, T. Akiyama and S. Yamada

J. Am. Chem. Soc. 123(20) (2001), 4855-4856

[200] Multiple Membranes from True Polyelectrolyte Multilayers

S. T. Dubas, T. R. Farhat and J. B. Schlenoff

J. Am. Chem. Soc. 123(22) (2001), 5368-5369

[201] Fabrication of Micro Reaction Cages with Tailored Properties

L. Dähne, S. Leporatti, E. Donath and H. Möhwald

J. Am. Chem. Soc. 123(23) (2001), 5431-5436
Hollow polyelectrolyte capsules in micro- and submicrometer size were prepared. Their interior was functionalized by a ''ship in bottle'' synthesis of copolymers. While the monomers permeated the capsule wall easily, the formed polymers remained in the capsule cage. The physicochemical properties of the capsule interior such as ion strength, pH, light absorption, and fluorescence could be controlled independently from the surrounding solvent by means of the chemical nature of the captured polymer. In case of polyelectrolytes the osmotic pressure of the counterions led to a swelling of the capsules which can be important for micromechanics. The functionalization with light-sensitive materials allowed selective photoreactions inside the capsules. Synthesis of polyelectrolytes at high concentration resulted in an intertwining of the capsule wall with the polymer. The modified walls behaved like ion exchange membranes and showed selectivity toward adsorption and permeation of organic ions. The modified capsules offer many possibilities for novel applications as containers for controlled precipitation, as nanoreactors for catalyzed reactions, or as sensors.

[202] Photoimaging Technique on Printing Al Plate via Self-Assembly Multilayer Films Based on Diazoresin

J. Y. Chen, H. Luo, B. X. Yang and W. X. Cao

J. Appl. Polym. Sci. 80(11) (2001), 1983-1987

A photoimaging technique on a printing aluminum plate (anodized oxidation Al plate) via self-assembly multilayer thin film from nitro-containing diazoresin (NDR) as cationic polyelectrolyte and various anionic polyelectrolytes has been developed. It was confirmed that, under UV-irradiation, the linkage nature of the films changes from ionic to covalent and the solubility of the films converts dramatically, that is, the exposed area of the film becomes insoluble in H2O-DMF-LiCl (2 :4: 1 wt %) ternary solvent, but mainly the unexposed area will be dissolved. After developing in ternary solvent, an image that accepts ink easily appears on the printing Al plate. To resolve the ink-stain problem, originating from a trace remainder of the NDR on the unexposed area of the Al plate, a surface modification technique by polyphosphoric acid, which reacts with NDR to form a hydrophilic surface, was developed. The thickness, homogeneity, and surface morphology of the multilayer film ton mica) determined by atomic force microscopy and UV-vis spectra were also reported. (C) 2001 John Wiley & Sons, Inc.

[203] The Study of Layer-by-Layer Ultrathin Films by the Dynamic Contact-Angle Method

J. Y. Chen, G. B. Luo and W. X. Cao

J. Colloid Interface Sci. 238(1) (2001), 62-69

The self-assembly film fabricated via the layer-by-layer technique was studied by the dynamic contact angle (DCA) method (wilhelmy plate method). The used polyelectrolytes are poly(diallyl-dimethylammonium chloride) (PDDA), poly(etheleneimine) (PEI), diphenylamine-4-diazonium- formaldehyde resin (DR), 2-nitro-N-methyl-4-diazonium- formaldehyde resin (NDR), and poly(sodium-p-styrenesulfonate) (PSS). For the self-assembly systems of PDDA/ PSS, PEI/PSS, DR/ PSS, and NDR/PSS, their individual contact angle fluctuates regularly with the fabrication of each layer, while the magnitude of different systems' contact angle depends on the participant polycation. The re-organization of components and the adjacent layer interpenetration are presented here to explain this phenomena. We also found that DR or NDR can adsorb itself via the layer-by-layer method to form multilayer him, and the hydrophobic interaction is put forward to effect this process. Moreover, the procedure of washing and drying after adsorption was studied and considered as a prerequisite for the successful fabrication, especially of the same charge carried components. (C) 2001 Academic Press.

[204] Preparation of Luminescent Polyelectrolyte/Cu-Doped ZnSe Nanoparticle Multilayer Composite Films

E. C. Hao, H. Zhang, B. Yang, H. Ren and J. C. Shen

J. Colloid Interface Sci. 238(2) (2001), 285-290

ZnSe and Cu-doped ZnSe nanoparticle aqueous suspensions were prepared in the presence of mercaptopropionic acid (MPA). Cu- doped ZnSe nanoparticles exhibited a strong blue emission that was strongly dependent upon the Cu dopant level and the chemical surface passivation produced by zinc-mercaptopropionic acid complexes. These Cu-doped ZnSe nanoparticles were further assembled into ultrathin polymer-supported films using electrostatic interactions and the layer-by-layer assembly method. UV-visible spectroscopy and X-ray photoelectron spectroscopy (XPS) provided evidence for the presence and optical activity of Cu-doped ZnSe nanoparticles within the polymer ultrathin films. Moreover, XPS data supported the presence of zinc mercaptopropionic acid complexes on nanoparticle surfaces and the presence of Cu+ ions with high luminescent activity in the doped nanoparticles. (C) 2001 Academic Press.

[205] Layer-by-Layer Construction of Novel Biofunctional Fluorescent Microparticles for Immunoassay Applications

W. J. Yang, D. Trau, R. Renneberg, N. T. Yu and F. Caruso

J. Colloid Interface Sci. 234(2) (2001), 356-362

A novel class of biofunctional fluorescent microparticles for application in immunoassays was constructed by using the layer- by-layer self-assembly method to deposit multiple layers of fluorescently labeled polyelectrolytes onto colloidal particles, followed by deposition of a protein (immunoglobulin G, IgG) layer. Microelectrophoresis experiments revealed alternating negative and positive zeta -potentials with deposition of each successive polyelectrolyte layer, indicating that the alternate electrostatic adsorption of polyelectrolytes of opposite charge was successfully achieved. Transmission electron microscopy images showed a change of the particle surface texture after polyelectrolyte multilayer deposition. Fluorescence microscopy image (FMI) analysis provided direct measurement of the fluorescence intensity of single microparticles. The observed systematic increase of the fluorescence intensity of individual microparticles with increasing polyelectrolyte layer number from FMI analysis further demonstrated the controlled regular adsorption of polyelectrolyte layers onto the polystyrene (PS) particles. Protein immobilization onto the polyelectrolyte multilayer- coated particles was verified by the different surface properties of the microparticles with respect to surface charge under pH conditions above and below the isoelectric point of the proteins. The assembly of IgG and fluorescein isothiocyanate-labeled IgG onto polyelectrolyte multilayer- coated PS microparticles and their potential use was ultimately confirmed by a solid phase immunotest. (C) 2001 Academic Press.

[206] Formation and Characterization of Heteropolyacid/Polycation Multilayer Films on Gold Electrode

Z. L. Cheng, L. Cheng, S. J. Dong and X. R. Yang

J. Electrochem. Soc. 148(5) (2001), E227-E232

Ultrathin multilayer films of a polybasic lanthanide heteropoly tungstate-molybdate complex and a cationic polymer of quaternized poly(4-vinylpyridine) partially complexed with osmium bis(2,2'-bipyridine) have been fabricated on a gold electrode precoated with a cysteamine self-assembled monolayer. The multilayer films have been characterized by optical spectroscopy, small-angle X-ray diffraction, and electrochemical methods (cyclic voltammetry and electrochemical impedance). Especially, the electrochemical impedance spectroscopy is developed to monitor the layer deposition processes. It provides important information such as double- layer capacitance and charge-transfer resistance. All obtained results reveal regular film growth with each layer adsorption. (C) 2001 The Electrochemical Society.

[207] Novel Polyelectrolyte Multilayer Microcapsule and Nanocapsule as Magnetic Carriers

A. Voigt, N. Buske, G. B. Sukhorukov, A. A. Antipov, S. Leporatti, H. Lichtenfeld, H. Baumler, E. Donath and H. Möhwald

J MAGN MAGN MATER