Influence of the polyelectrolyte molecular weight on exponentially growing multilayer films in the linear regime

Alternated deposition of polyanions and polycations on a charged solid substrate leads to the buildup of polyelectrolyte multilayer (PEM) films. Two types of PEM films were reported in the literature: films whose thickness increases linearly and films whose thickness increases exponentially with the number of deposition steps. However, it was recently found that, for exponentially growing films, the exponential increase of the film thickness takes place only during the initially deposited pairs of layers and is then followed by a linear increase. In this study, we investigate the growth process of hyaluronic acid/poly(L-lysine) (HA/PLL) and poly(L-glutamic acid)/poly(allylamine) (PGA/PAH) films, two films whose growth is initially exponential, when the growth process enters the linear regime. We focus, in particular, on the influence of the molecular weight (Mw) of the polyelectrolytes. For both systems, we find that the film thickness increment per polyanion/polycation deposition step in the linear growth regime is fairly independent of the molecular weights of the polyelectrolytes. We also find that when the (HA/PLL)n films are constructed with low molecular weight PLL, these chains can diffuse into the entire film during each buildup cycle, even for very thick films, whereas the PLL diffusion of high molecular weight chains is restricted to the upper part of the film. Our results lead to refinement of the buildup mechanism model, introduced previously for the exponentially growing films, which is based on the existence of three zones over the entire film thickness. The mechanism no longer needs all the "in" and "out" diffusing polyanions or polycations to be involved in the buildup process to explain the linear growth regime but merely relies on the interaction between the polyelectrolytes with an upper zone of the film. This zone is constituted of polyanion/polycation complexes which are "loosely bound" and rich in the polyelectrolyte deposited during the former deposition step.     

Layer by layer buildup of polysaccharide films: physical chemistry and cellular adhesion aspects

The formation ofpolysaccharide films based on the alternate deposition of chitosan (CHI) and hyaluronan (HA) was investigated by several techniques. The multilayer buildup takes place in two stages: during the first stage, the surface is covered by isolated islets that grow and coalesce as the construction goes on. After several deposition steps, a continuous film is formed and the second stage of the buildup process takes place. The whole process is characterized by an exponential increase of the mass and thickness of the film with the number of deposition steps. This exponential growth mechanism is related to the ability of the polycation to diffuse "in" and "out" of the whole film at each deposition step. Using confocal laser microscopy and fluorescently labeled CHI, we show that such a diffusion behavior, already observed with poly(L-lysine) as a polycation, is also found with CHI, a polycation presenting a large persistence length. We also analyze the effect of the molecular weight (MW) of the diffusing polyelectrolyte (CHI) on the buildup process and observe a faster growth for low MW chitosan. The influence of the salt concentration during buildup is also investigated. Whereas the CHI/HA films grow rapidly at high salt concentration (0.15 M NaCl) with the formation of a uniform film after only a few deposition steps, it is very difficult to build the film at 10(-4) M NaCl. In this latter case, the deposited mass increases linearly with the number of deposition steps and the first deposition stage, where the surface is covered by islets, lasts at least up to 50 bilayer deposition steps. However, even at these low salt concentrations and in the islet configuration, CHI chains seem to diffuse in and out of the CHI/HA complexes. The linear mass increase of the film with the number of deposition steps despite the CHI diffusion is explained by a partial redissolution of the CHI/HA complexes forming the film during different steps of the buildup process. Finally, the uniform films built at high salt concentrations were also found to be chondrocyte resistant and, more interestingly, bacterial resistant. Therefore, the (CHI/HA) films may be used as an antimicrobial coating.     

Thickness, surface morphology, and optical properties of porphyrin multilayer thin films assembled on Si(100) using copper(I)-catalyzed azide-alkyne cycloaddition

We report the structure, optical properties and surface morphology of Si(100) supported molecular multilayers resulting from a layer-by-layer (LbL) fabrication method utilizing copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC), also known as "click" chemistry. Molecular based multilayer films comprised of 5,10,15,20-tetra(4-ethynylphenyl)porphyrinzinc(II) (1) and either 1,3,5-tris(azidomethyl)benzene (2) or 4,4'-diazido-2,2'-stilbenedisulfonic acid disodium salt (3) as a linker layer, displayed linear growth properties up to 19 bilayers. With a high degree of linearity, specular X-ray reflectivity (XRR) measurements yield an average thickness of 1.87 nm/bilayer for multilayers of 1 and 2 and 2.41 nm/bilayer for multilayers of 1 and 3. Surface roughnesses as determined by XRR data fitting were found to increase with the number of layers and generally were around 12% of the film thickness. Tapping mode AFM measurements confirm the continuous nature of the thin films with roughness values slightly larger than those determined from XRR. Spectroscopic ellipsometry measurements utilizing a Cauchy model mirror the XRR data for multilayer growth but with a slightly higher thickness per bilayer. Modeling of the ellipsometric data over the full visible region using an oscillator model produces an absorption profile closely resembling that of a multilayer grown on silica glass. Comparing intramolecular distances from DFT modeling with experimental film thicknesses, the average molecular growth angles were estimated between 40° and 70° with respect to the substrate surface depending on the bonding configuration.     

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.     

Supported lipid bilayers on biocompatible polysaccharide multilayers

Formation of supported lipid bilayers on soft polymer cushions is a useful approach to decouple the membrane from the substrate for applications involving membrane proteins. We prepared biocompatible polymer cushions by the layer-by-layer assembly of two polysaccharide polyelectrolytes, chitosan (CHI) and hyaluronic acid, on glass and silicon substrates. (CHI/HA)(5) films were characterized by atomic force microscopy, giving an average thickness of 57 nm and roughness of 25 nm in aqueous solution at pH 6.5. Formation of zwitterionic lipid bilayers by the vesicle fusion method was attempted using DOPC vesicles at pH 4 and 6.5 on (CHI/HA)(5) films. At higher pH adsorbed lipids had low mobility and large immobile lipid fractions; a combination of fluorescence and AFM indicated that this was attributable to formation of poor quality membranes with defects and pinned lipids rather than to a layer of surface-adsorbed vesicles. By contrast, more uniform bilayers with mobile lipids were produced at pH 4. Fluorescence recovery after photobleaching gave diffusion coefficients that were similar to those for bilayers on PEG cushions and considerably higher than those measured on other polyelectrolyte films. The results suggest that the polymer surface charge is more important than the surface roughness in controlling formation of mobile supported bilayers. These results demonstrate that polysaccharides provide a useful alternative to other polymer cushions, particularly for applications where biocompatibility is important.     

Real-time analysis of enzymatic surface-initiated polymerization using surface plasmon resonance (SPR)

The kinetics of enzymatic surface-initiated polymerization of PHB on gold surface has been examined by SPR and the resultant polymer layers characterized by AFM and FT-IR spectrometry. The immobilized enzyme catalyzed surface-initiated polymerization of 3HB-CoA, resulting in the formation of a polymer brush on the surface. The rate of polymer growth from the surface was monitored by SPR in real-time. Polymer growth as measured by the increase in the resonance angle showed no apparent lag phase during the polymerization reaction. SPR analysis also revealed that the thickness of the polymer film could be controlled by varying the initial enzyme density on the surface. The average thicknesses of the PHB film after polymerization reaction were 95, 45 and 15 nm for the surfaces that were treated with 0.5, 0.3 and 0.1*10(-6) M of enzyme, respectively. The binding of PHA synthase at different concentration to the mixed SAMs and subsequent polymerization.     

pH-controlled exponential and linear growing modes of layer-by-layer assemblies of star polyelectrolytes

We report the unique layer-by-layer (LbL) assembly behavior of pH-sensitive star-shaped polyelectrolytes with both linear and exponential growth modes controlled by star architecture and assembly conditions. Cationic poly[2-(dimethylamino)ethyl methacrylate] and anionic poly(acrylic acid) stars were synthesized via "core-first" atom-transfer radical polymerization (ATRP) based on multifunctional initiators, in addition to their linear analogues. We demonstrated the LbL growth behavior as a function of deposition pH (ranging from 5 to 7), number of layers (up to 30 bilayers), and the method of assembly (dip- vs spin-assisted LbL). The spin-assisted LbL assembly makes it possible to render smoother and thinner LbL films with parameters controlled by the shear rate and pH conditions. In contrast, for dip-assisted LbL assembly, the pH-dependent exponential growth was observed for both linear and star polyelectrolytes. In the case of linear/linear pair, the exponential buildup was accompanied with a notable surface segregation which resulted in dramatic surface nonuniformity, "wormlike" heterogeneous morphology, and dramatic surface roughening. In contrast, star/linear and star/star LbL films showed very uniform and smooth surface morphology (roughness below 2.0 nm on the scale of 10 μm × 10 μm) with much larger thickness reaching up to 1.0 μm for 30 bilayers and rich optical interference effects. Star polyelectrolytes with partially screened charges and high mobility caused by compact branched architecture appear to facilitate fast diffusion and exponential buildup of LbL films. We suggest that the fast buildup prevents long-range lateral diffusion of polyelectrolyte star components, hinders large-scale microphase separation, and thus leads to unique thick, smooth, uniform, transparent, and colorful LbL films from star polyelectrolytes in contrast to mostly heterogeneous films from traditional linear counterparts.     

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.     

Preparation and characterization of thin films of SiO(x) on gold substrates for surface plasmon resonance studies

We report here on the fabrication and characterization of stable thin films of amorphous silica (SiO(x)) deposited on glass slides coated with a 5 nm adhesion layer of titanium and 50 nm of gold, using the plasma-enhanced chemical vapor deposition (PECVD) technique. The resulting surfaces were characterized using atomic force microscopy (AFM), ellipsometry, contact angle measurements, and surface plasmon resonance (SPR). AFM analysis indicates that homogeneous films of silica with low roughness were formed on the gold surface. The deposited silica films showed excellent stability in different solvents and in piranha solution. There was no significant variation in the thickness or in the SPR signal after these harsh treatments. The Au/SiO(x) interfaces were investigated for their potential applications as new surface plasmon resonance sensor chips. Silica films with thicknesses up to 40 nm allowed visualization of the surface plasmon effect, while thicker films resulted in the loss of the SPR characteristics. SPR allowed further the determination of the silica thickness and was compared to ellipsometric results. Chemical treatment of the SiO(x) film with piranha solution led to the generation of silanol surface groups that have been coupled with a trichlorosilane.     

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) 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. The nanoporous structure of the multilayer film was further confirmed by the surface morphology analysis using atomic force microscopy (AFM).     

不同分子量PEG的铜电镀液对电化学沉积铜行为的研究

研究了在酸性镀铜溶液中添加不同分子量的PEG对直径为50微米、深径比为1的镀层盲孔填充效果的影响.结果表明,随着PEG分子量的增加,电镀铜溶液的微孔填充力明显提高.电流密度为2 A/dm2,添加剂PEG分子量(u)超过6000时,镀液可以完全填充盲孔,镀层不出现任何空洞和缝隙.这是由于添加剂PEG能明显加强电镀铜镀液阴极极化,抑制了电镀铜的沉积.同时,PEG于镀液中的扩散系数还随其分子量的增加而降低,从而增加了SPS在微孔底部的吸附力,加速了电镀铜在微孔底部的沉积.进一步,增大PEG分子量,沉积铜膜的表面粗糙度、铜膜结晶度和电阻率均有所降低.     

Covalently linked DNA/protein multilayered film for controlled DNA release

A stable, biocompatible single strand DNA (ssDNA)/bovine serum albumin (BSA) multilayered film for control release of DNA was fabricated on PEI-coated quartz slides, gold-evaporated plates and silicon wafers, respectively through a formaldehyde-induced, covalently linked layer-by-layer (LBL) assembly technique. The constructed film structure was well characterized by using UV-vis spectrometry, surface plasmon resonance (SPR) and atomic force microscopy (AFM). The results showed that the DNA incorporated LBL film was fabricated successfully and the amount of ssDNA and BSA in the film could be tailored simply by controlling the number of the bilayers. The control release of DNA from the film was also monitored in this study. UV-vis spectrometry, SPR and AFM measurements indicated that the release of ssDNA and amino acid was adjustable by changing the proteinase K incubation time. This biocompatible covalently assembled film demonstrates an innovative approach to engineer a DNA/protein based nanostructure for controlled DNA release, which could provide stability, controllability and flexibility superior to that of LBL film assembled by electrostatic attraction. Since the film in this work can be assembled on different substrates, it is very feasible to fabricate nanoparticle-based gene therapy systems with this new approach and to have great potential in biomedical applications.     

Chitosan adsorption on hydroxyapatite and its role in preventing acid erosion

Polymer adsorption onto an artificial saliva (AS) layer is investigated using quartz-crystal microbalance with dissipation (QCM-D) and chitosan as the model polymer. QCM-D is utilized in an innovative manner to monitor in situ adsorption of chitosan (CH) onto a hydroxyapatite (HA) coated crystal and to examine the ability of the adsorbed layer to "protect" the HA upon sequential exposure to acidic solutions. After deposition of a thin AS layer (16nm), the total thickness on the HA substrate increases to 37nm upon exposure to CH at pH 5.5 for 10min. Correspondingly, the surface charge changes from negative (i.e., AS) to positive, consistent with the adsorption the polycationic CH onto or into the AS layer. Upon exposure to an oxidizing agent, the chitosan cross-links and collapses as noted by a decrease in thickness to 10nm and an increase in the shear modulus by an order of magnitude. Atomic force microscopy (AFM) is used to determine the surface morphology and RMS roughness of the coated and HA surfaces after citric acid challenges. Both physisorbed and cross-linked chitosan are demonstrated to limit and prevent the erosion of HA, respectively.     

In situ fabrication of silver nanoarrays in hyaluronan/PDDA layer-by-layer assembled structure

We present a simple in situ method to fabricate silver (Ag) nanoparticle arrays in a layer-by-layer (LBL) assembled hyaluronan (HA)/poly(dimethyldiallylammonium chloride) (PDDA) multilayer structure, in which the LBL multilayered film is constructed by electrostatic attraction between positively charged PDDA and negatively charged HA, followed by in situ synthesis of embedded Ag nanoparticle arrays in the LBL "nanoreactors," where the abundant negatively charged carboxyl groups of HA bind and further reduce Ag(+) ions under UV-irradiating. The arrays morphology is highly dependent on the number of bilayers, and the surface density of nanoparticles in the arrays can be simply tailored by the number of irradiation/drying cycles during fabrication. The embedded Ag nanoparticle arrays possess good stability for localized surface plasmon resonance (SPR) absorption spectrum-based biosensors and superior antimicrobial capability. These render great potentials for the films in both biosensing and antimicrobial applications.     

Characterization of the physical properties of model biomembranes at the nanometer scale with the atomic force microscope

Interaction forces and topography of mixed phospholipid-glycolipid bilayers were investigated by atomic force microscopy (AFM) in aqueous conditions with probes functionalized with self-assembled monolayers terminating in hydroxy groups. Short-range repulsive forces were measured between the hydroxy-terminated probe and the surface of the two-dimensional (2-D) solid-like domains of distearoyl-phosphatidylethanolamine (DSPE) and digalactosyldiglyceride (DGDG). The form and range of the short-range repulsive force indicated that repulsive hydration/steric forces dominate the interaction at separation distances of 0.3-1.0 nm after which the probe makes mechanical contact with the bilayers. At loads < 5 nN the bilayer was elastically deformed by the probe, while at higher loads plastic deformation of the bilayer was observed. Surprisingly, a short-range repulsive force was not observed at the surface of the 2-D liquid-like dioleoylphosphatidylethanolamine (DOPE) film, despite the identical head groups of DOPE and DSPE. This provides direct evidence for the influence of the structure and mechanical properties of lipid bilayers on their interaction forces, an effect which may be a major importance in the control of biological processes such as cell adhesion and membrane fusion. The step height measured between lipid domains in the AFM topographic images was larger than could be accounted for by the thickness and mechanical properties of the molecules. A direct correlation was observed between the repulsive force range over the lipid domains and the topographic contrast, which provides direct insight into the fundamental mechanisms of AFM imaging in aqueous solutions. This study demonstrates that chemically modified AFM probes can be used in combination with patterned lipid bilayers as a novel and powerful approach to characterize the nanometer scale chemical and physical properties of heterogeneous biosurfaces such as cell membranes.     

The basic research on physiological property of functionalized hyaluronan—I. Effect of hyaluronan and sulfated hyaluronan on cell proliferation of human epidermal keratinocytes

Hyaluronan (HA) is one of the polysaccharides that is found widely in connective tissue of mammals, and it has no sulfate group and high molecular weight in comparison with other glycosaminoglycans. Glycosaminoglycans are deeply concerned with the manifestation of biofunctions not only by their physical properties but also by physiological ones. In this study, sulfated HA (S‐HA) with various degrees of sulfate substitution and high molecular weight will be synthesized in order to give HA new biological functions. Moreover, the effect of HA and S‐HA on cell proliferation of human epidermal keratinocytes in vitro will be discussed. HA did not affect lag phase, but growth rate (metabolic turnover) of the cell in a logarithmic growth phase which was controlled by the molecular weight of HA. S‐HA stimulated the cell proliferation in the low concentration region under 1 μg/ml. While it inhibited the cell proliferation in the high concentration region over 10 μg/ml. It strongly suppressed the cell proliferation in the logarithmic growth metaphase. These facts were considered to be caused by the change of the cell‐matrix and/or cell–cell interactions. Copyright © 2004 John Wiley & Sons, Ltd.     

Buildup mechanism of carboxymethyl cellulose and chitosan self-assembled films

Films with different numbers of layers have been built by alternating the adsorption of carboxymethyl cellulose (CMC) and chitosan (CHI) at different pH levels. The adsorption process was recorded by quartz crystal microbalance (QCM). The results showed that under all pH conditions considered, the growth of the films is nonlinear. The film construction performed at pH 4.0 (preferred assembly pH) with different numbers of bilayers (CMC/CHI as one bilayer) was also observed step by step by atomic force microscopy (AFM). Comparing the growth process from QCM with the surface morphological changes from AFM shows the existence of an inhomogeneous structure for the first nine bilayers, and, after a coalescence of islands, an increase in the number of bilayers was demonstrated. The possible growth mechanism was also evaluated.     

纳米多孔金薄膜的表面等离子体共振传感特性

对淀积在玻璃衬底上厚度约60 nm的金银合金溅射薄膜进行硝酸腐蚀脱银处理, 得到纳米多孔金薄膜. 利用自建的波长检测型表面等离子体共振(SPR)传感装置研究了腐蚀时间对纳米多孔金薄膜SPR特性的影响, 结果发现纳米多孔金薄膜与水溶液接触后在400-900 nm光谱范围内不具有SPR效应, 而当薄膜置于空气中时会产生明显的传播等离子体共振吸收峰, 其共振波长随腐蚀时间增加逐渐红移. 纳米多孔金薄膜在空气气氛中的SPR效应使其能够用于原位监测气相分子在孔内的吸附, 还可对在液相中吸附的生化分子进行离位测试. 本文对L-谷胱甘肽、L-半胱氨酸、2-氨基乙硫醇三种含巯基的生化小分子在纳米多孔金薄膜内的吸附进行了离位分析, 结果表明与传统的致密金薄膜SPR芯片比较, 纳米多孔金薄膜对这些分子显示出更高的灵敏度和更低的检测下限, 这归功于多孔金的大比表面积使其能够吸附大量的生化小分子. 实验还对乙醇蒸气在纳米多孔金薄膜内的吸附进行了原位监测, 发现吸附平衡所用时间较长, 约为160 min.     

Layer-by-layer assembly of partially sulfonated isotactic polystyrene with poly(vinylamine)

The stereoregular synthetic polymer isotactic polystyrene bearing partially sulfonated groups (SiPS) was used as a layer-by-layer assembled thin film for the first time. When a low molecular weight compound was employed as the pair for the alternative layer-by-layer (LbL) assembly, the frequency shift was very small using quartz crystal microbalance (QCM) analysis, whereas poly(vinylamine) (PVAm) formed an effective pair for the construction of LbL films with SiPS. When it was neutralized, SiPS was not assembled, probably due to the loss of effective polymer-polymer interactions. The ionic strength conditions revealed a slight difference of the assembly behavior on the isotactic polymer as compared to the atactic one. The assembled LbL film showed the same peaks over the range from 1141 to 1227 cm(-1) and 700 cm(-1) in the FT-IR/ATR spectra as the bulk complex of SiPS/PVAm, and the thickness on one side was calculated at 76 nm by QCM analysis. The surface roughness of the film was also observed by AFM.     

Phosphatidylserine/Cholesterol Bilayers Supported on a Polycation/Alkylthiol Layer Pair

1-Stearoyl-2-oleoyl phosphatidylserine (SOPS)/cholesterol bilayers, supported on a polycation/alkylthiol layer pair on a gold surface, were investigated by surface plasmon resonance (SPR) and fluorescence recovery after photobleaching. The substrate was formed by electrostatic adsorbance of a hydrated poly(diallyldimethylammonium chloride) (PDDA) layer on the negatively charged surface of a self-assembled monolayer of 11-mercaptoundecanoic acid (MUA) on gold. Lipid membranes with different SOPS/cholesterol compositions were deposited on the PDDA/MUA layer pair by vesicle fusion. When the cholesterol content was below 20%, single bilayers were deposited. Fluorescence recovery after the bleaching experiments revealed that the SOPS/cholesterol bilayers were mobile at room temperature; lateral diffusion coefficients of a fluorescence probe were approximately 1x10(-9) cm(2)/s. The kinetics of the addition of the ion-channel-forming peptide gramicidin to the supported bilayers was detected by SPR. Copyright 2000 Academic Press.