Preparation and characterization of polyelectrolyte-coated gold nanoparticles

Gold nanoparticles of 5 nm diameter, stabilized by 4-(dimethylamino)pyridine (DMAP), were coated with poly(sodium 4-styrene sulfonate) (PSS) via electrostatic self-assembly. The suspension stability, monitored by the gold surface plasmon band (SPB), was studied by varying the pH, the PSS chain length, and PSS concentration. Enhanced stability is obtained at pH 10 (above the pKa of DMAP) when the polymer chain length matches or exceeds the particle circumference. Solid state 13C NMR was used to determine the presence of DMAP and polymers after subsequent deposition of weak and strong polycations: poly(allylamine hydrochloride) (PAH) and poly(diallyldimethylammonium chloride) (PDADMAC). At pH 10, DMAP remains associated with the nanoparticle after the first PSS layer has been formed. When PAH or PDADMAC are subsequently added at pH 4.5, DMAP is expelled, the suspensions remain stable, and zeta potential values indicate complete charge reversal. In the case of PDADMAC, however, the first layer of PSS is not fully retained. When PDADMAC is added at pH 10, DMAP and the first PSS layer are retained but lower zeta potentials and a higher SPB shift indicate a degraded stability. For PAH addition at pH 9.5, both DMAP and PSS are expelled and the suspension becomes unstable. These differences in stability of the multilayer components and the nanoparticle suspension are rationalized in terms of chain flexibility, polymer charge density, and the ability of the polymer functional groups to directly interact with the gold surface.     

Cross-linked poly(vinyl alcohol) as permanent hydrophilic column coating for capillary electrophoresis.

A fast method for the generation of permanent hydrophilic capillary coatings for capillary electrophoresis (CE) is presented. Such interior coating is effected by treating the surface to be coated with a solution of glutaraldehyde as cross-linking agent followed by a solution of poly(vinyl alcohol) (PVA), which results in an immobilization of the polymer on the capillary surface. Applied for capillary zone electrophoresis (CZE) such capillaries coated with cross-linked PVA exhibit excellent separation performance of adsorptive analytes like basic proteins due to the reduction of analyte-wall interactions. The long-term stability of cross-linked PVA coatings could be proved in very long series of CZE separations. More than 1000 repetitive CE separations of basic proteins were performed with stable absolute migration times relative standard deviation (RSD > 1.2%) and without loss of separation efficiency. Cross-linked PVA coatings exhibit a suppressed electroosmotic flow and excellent stability over a wide pH range.     

Practical considerations for preparing polymerized phospholipid bilayer capillary coatings for protein separations

Phosphorylcholine (PC) based phospholipid bilayers have proven useful as capillary coating materials due to their inherent resistance to non-specific protein adsorption. The primary limitation of this important class of capillary coatings remains the limited long-term chemical and physical stability of the coatings. Recently, a method for increasing phospholipid coating stability in fused silica capillaries via utilization of polymerized, synthetic phospholipids was reported. Here, we expand upon these studies by investigating polymerized lipid bilayer capillary coatings with respect to separation performance including run-to-run, day-to-day and column-to-column reproducibility and long-term stability. In addition, the effects of pH and capillary inner diameter on polymerized phospholipid coated capillaries were investigated to identify optimized coating conditions. The coatings are stabilized for protein separations across a wide range of pH values (4.0–9.3), a unique property for capillary coating materials. Additionally, smaller inner diameter capillaries (≤50 μm) were found to yield marked enhancements in coating stability and reproducibility compared to wider bore capillaries, demonstrating the importance of capillary size for separations employing polymerized phospholipid coatings.     

Electrophoretic separation of environmentally important phenolic compounds using montomorillonite-coated fused-silica capillaries

This paper reports a simple procedure for coating fused-silica capillaries with poly(diallyldimethyl ammonium chloride) and montmorillonite. The coated capillaries were characterized by performing EOF measurements as a function of buffer pH, number of layers of coating, and number of runs (stability). The coated capillaries showed a highly stable mu(EOF) (run-to-run RSD less than 1.5%, n = 20), allowing continuous use for several days without conditioning. The coated capillaries were then used for the effective separation of nine environmentally important phenolic compounds showing a significant improvement in the resolution, when compared to bare fused-silica capillaries. The EOF of the coated capillaries was constant in alkaline solutions (pH > or = 7), allowing the optimization of the separation conditions of phenolic compounds without significantly affecting the mu(EOF).     

Efficient and highly reproducible capillary electrophoresis-mass spectrometry of peptides using Polybrene-poly(vinyl sulfonate)-coated capillaries

The potential of capillaries noncovalently coated with a bilayer of oppositely charged polymers for the analysis of peptides by CE-MS was investigated. Bilayer coatings were produced by subsequently rinsing fused-silica capillaries with a solution of Polybrene (PB) and poly(vinyl sulfonate) (PVS). The PB-PVS coating showed to be fully compatible with MS detection causing no ionization suppression or background signals. The bilayer coating provided a considerable EOF at low pH, thereby facilitating the fast separation of peptides using a BGE of formic acid (pH 2.5). Under optimized CE-MS conditions, for enkephalin peptides high separation efficiencies were obtained with plate numbers in the range of 300,000-500,000. It is demonstrated that both the cancellation of the hydrodynamic capillary flow induced by the nebulizer gas and a sufficiently high-data acquisition rate are crucial for achieving these efficiencies. The overall performance of the CE-MS system using PB-PVS-coated capillaries was evaluated by the analysis of a tryptic digest of cytochrome c. The system provided an efficient separation of the peptide mixture, which could be effectively monitored by MS/MS detection allowing identification of at least 13 peptides within a time interval of 1.5 min. In addition, the PB-PVS coating proved to be very consistent yielding stable CE-MS patterns with highly favorable migration time reproducibilities (RSDs < 1% over a 3-day period).     

High-flux nanofiltration membranes prepared by adsorption of multilayer polyelectrolyte membranes on polymeric supports

Layer-by-layer deposition of anionic and cationic polyelectrolytes readily converts polymeric ultrafiltration membranes into materials capable of nanofiltration. ATR-FTIR spectra confirm that layer-by-layer deposition occurs on the ultrafiltration substrates, and adsorption of as few as 2.5 bilayers of poly(styrenesulfonate) (PSS)/protonated poly(allylamine) (PAH) or 3.5 bilayers of PSS/poly(diallyldimethylammonium chloride) (PDADMAC) reduces the molecular weight cutoff of polyethersulfone ultrafiltration supports from 50 kDa to <500 Da. Deposition of multilayer polyelectrolyte films on 300 and 500 kDa membranes also decreases molecular weight cutoffs, but solute rejections are significantly lower when using these supports, suggesting that the polyelectrolyte films do not completely cover large (0.2-0.4 microm in diameter) pores. On the 50 kDa substrates, PSS/PDADMAC films containing 3.5 bilayers exhibit a 95% rejection of SO(4)(2-) and a chloride/sulfate selectivity of 27, whereas 4.5-bilayer PSS/PAH coatings show a glucose/raffinose selectivity of 100. Pure water flux for [PSS/PAH](3)PSS-coated membranes at 4.8 bar is 1.6 m(3)/(m(2)day), which is more than 2-fold higher than that through a commercial 500 Da membrane.     

Capillaries modified by noncovalent anionic polymer adsorption for capillary zone electrophoresis, micellar electrokinetic capillary chromatography and capillary electrophoresis mass spectrometry

A simple coating procedure for generation of a high and pH-independent electroosmotic flow in capillary zone electrophoresis (CZE) and micellar electrokinetic capillary chromatography (MEKC) is described. The bilayer coating was formed by noncovalent adsorption of the ionic polymers Polybrene and poly(vinylsulfonate) (PVS). A stable dynamic coating was formed when PVS was added to the background electrolyte. Thus, when the PVS concentration in the background electrolyte was optimized for CZE (0.01%), the EOF differed less than 0.3% after 54 runs. The electroosmotic mobility in the coated capillaries was (4.9+/-0.1) x 10(-4) cm2V(-1)s(-1) in a pH-range of 2-10 (ionic strength = 30 mM). When alkaline compounds were used as test substances intracapillary and intercapillary migration time variations (n = 6) were less than 1% relative standard deviation (RSD) and 2% RSD, respectively in the entire pH range. The coating was fairly stable in the presence of sodium dodecyl sulfate, and this made it possible to perform fast MEKC separations at low pH. When neutral compounds were used as test substances, the intracapillary migration time variations (n = 6) were less than 2% RSD in a pH range of 2-9. In addition to fast CZE and MEKC separations at low pH, analysis of the alkaline compounds by CE-MS was also possible.     

Micellar electrokinetic chromatography at low pH with polyelectrolyte-coated capillaries

The performance of capillaries coated with a poly(diallyldimethylammonium) (PDADMA) monolayer or poly(diallyldimethylammonium)-poly(styrenesulfonate) bilayer was investigated and compared under micellar electrokinetic chromatographic (MEKC) conditions. Both monolayer (positively charged) and bilayer (negatively charged) coatings with micellar (sodium dodecyl sulfate) electrolyte generated very stable and pH-independent cathodal electroosmotic flow (EOF). From the results obtained, it can be concluded that in a doubly coated capillary the second poly(styrenesulfonate) layer is replaced by sodium dodecyl sulfate micelles during flushing with micellar electrolyte. Consequently, in order to obtain a stable and pH-independent cathodal electroosmotic flow for the MEKC separations, the capillary coating with the second polyanion layer is not necessary. The importance of the PDADMA coating was illustrated by comparing MEKC separations of the common developing agents (hydroquinone, phenidone, pyrocatechol, pyrogallol and quinone) on a bare uncoated capillary with the coated capillary. The coating provides reproducible MEKC separations at low pH (pH 3.0) with relative standard deviation (R.S.D.) values for migration times and peak areas lower than 0.45 and 3.3%, respectively. Good linearities in the range from 5 x 10(-5) to 2 x 10(-3) mol l(-1) were obtained for all five compounds, with correlation coefficients higher than 0.998. The detection limits were in the range from 5 x 10(-6) mol l(-1) for pyrocatechol to 2 x 10(-5) mol l(-1) for quinone. The proposed MEKC system was applied to the determination of hydroquinone and phenidone in X-ray photographic developer solutions.     

Capillary electrophoresis using core‐based hyperbranched polyethyleneimine (CHPEI) static‐coated capillaries

With unique 3‐D architecture, the application of core‐based hyperbranched polyethyleneimine (CHPEI), as a capillary coating in capillary electrophoresis, is demonstrated by manipulation of the electroosmotic mobility (EOF). CHPEI coatings (CHPEI5, M_w ≈? 5000 and CHPEI25, M_w ≈? 25 000) were physically adsorbed onto the inner surface of bare fused‐silica capillary (BFS) via electrostatic interaction of the oppositely charged molecules by rinsing the capillaries with different CHPEI aqueous solutions. The EOF values of the coated capillaries were measured over the pH range of 4.0–9.0. At higher pH (pH >6) the coated capillary surface possesses excess negative charges, which causes the reversal of the EOF. The magnitudes of the EOF obtained from the coated capillaries were three‐fold lower than that of BFS capillary. Desirable reproducibility of the EOF with % RSD (n = 5) ? 2 was obtained. Effect of ionic strength, stability of the coating (% RSD = 0.3) and the dependence of the EOF on pH (% RSD = 0.5) were also investigated. The CHPEI‐coated capillaries were successfully utilized to separate phenolic compounds, B vitamins, as well as basic drugs and related compounds with reasonable analysis time (<20 min) and acceptable migration‐time repeatability (<0.7% RSD for intra‐capillary and <2% RSD for inter‐capillary).     

Hollow polyelectrolyte multilayer tubes: mechanical properties and shape changes

In this paper, novel hollow polyelectrolyte multilayer tubes from poly(diallyldimethylammonium chloride) (PDADMAC), poly(styrene sulfonate) (PSS), and poly(allylamine hydrochloride) (PAH) were prepared: Readily available glass fiber templates are coated with polyelectrolytes using the layer-by-layer technique, followed by subsequent fiber dissolution. Depending on the composition of the polymeric multilayer, stable hollow tubes or tubes showing a pearling instability are observed. This instability corresponds to the Rayleigh instability and is a consequence of an increased mobility of the polyelectrolyte chains within the multilayer. The well-defined stable tubes were characterized with fluorescence microscopy, confocal laser scanning microscopy, and atomic force microscopy (AFM). The tubes were found to be remarkably free of defects, which results in an impermeable tube wall for even low molecular weight molecules. The mechanical properties of the tubes were determined with AFM force spectroscopy in water, and because continuum mechanical models apply, the Young's modulus of the wall material was determined. Additionally, scaling relations for the dependency of tube stiffness on diameter and wall thickness were validated. Because both parameters can be experimentally controlled by our approach, the deformability of the tubes can be varied over a broad range and adjusted for the particular needs.     

Counterions and water in polyelectrolyte multilayers: a tale of two polycations

Attenuated total internal reflectance Fourier transform infrared, ATR-FTIR, spectroscopy was used to compare the water uptake and doping within polyelectrolyte multilayers made from poly(styrene sulfonate), PSS, and a polycation, either poly(allylamine hydrochloride), PAH, or poly(diallyldimethylammonium chloride), PDADMAC. Unlike PDADMA/PSS multilayers, whose water content depended on the solution ionic strength, PAH/PSS multilayers were resistant to doping by NaCl to a concentration of 1.2 M. Using (infrared active) perchlorate salt, the fraction of residual counterions in PDADMA/PSS and PAH/PSS was determined to be 3% and 6%, respectively. The free energy of association between the polymer segments, in the presence of NaClO4, was about 5 kJ mol-1 and -10 kJ mol-1, respectively, for PDADMA/PSS and PAH/PSS, indicating the relatively strong association between the polymer segments in the latter relative to the former. Varying the pH of the solution in contact with the PAH/PSS multilayer revealed a transition to a highly swollen state, interpreted to signal protonation of PAH under much more basic conditions than the pKa of the solution polymer. The increase in the multilayer pKa suggested an interaction energy for PAH/PSS in NaCl of ca. 16 kJ mol-1.     

仿生制备有机-无机复合微囊固定化葡萄糖氧化酶

将层层自组装技术与仿生矿化技术相结合,由聚苯乙烯磺酸钠、聚二甲基二烯丙基氯化铵和二氧化硅成功制备(聚苯乙烯磺酸钠-聚二甲基二烯丙基氯化铵)₂-二氧化硅复合微囊.采用扫描电子显微镜、红外光谱和热重对微囊的形貌和化学结构进行了表征.以该复合微囊作为理想载体固定化葡萄糖氧化酶.结果表明,固定于复合微囊中的葡萄糖氧化酶的热稳定性、pH稳定性、操作稳定性得到了提高;在最适条件下,复合微囊固定化葡萄糖氧化酶的酶活回收率为72.85%,米氏常数是游离葡萄糖氧化酶的2.21倍.复合微囊在化学/生物催化、药物/基因传递系统和生物传感器应用方面具有一定的潜能.     

Multilayer polyelectrolyte films as nanofiltration membranes for separating monovalent and divalent cations

Alternating adsorption of polyanions and polycations on porous supports provides a convenient way to prepare ion-selective nanofiltration membranes. This work examines optimization of ultrathin, multilayer polyelectrolyte films for monovalent/divalent cation separations relevant to water softening. Membranes composed of five bilayers of poly(styrene sulfonate)/poly(allylamine hydrochloride) (PSS/PAH) on porous alumina supports allow a solution flux of 0.85 m³/(m² day) at 4.8 bar, and exhibit 95% rejection of MgCl₂ along with a Na⁺/Mg²⁺ selectivity of 22. Similar results were obtained in Na⁺/Ca²⁺ separations. PSS/poly(diallyl-dimethylammonium chloride) (PDADMAC) films permit higher fluxes than PSS/PAH systems due to the higher swelling of films containing PDADMAC, but the Mg²⁺ rejection by PSS/PDADMAC membranes is less than 45%. However, capping PSS/PDADMAC films with a bilayer of PSS/PAH yields Mg²⁺ rejections and Na⁺/Mg²⁺ selectivities that are typical of pure PSS/PAH membranes. Separation performance can be optimized through control over deposition conditions (pH and supporting electrolyte concentration) and the charge of the outer layer since Donnan exclusion is a major factor in monovalent/divalent cation selectivity. Streaming potential measurements demonstrate that the magnitude of positive surface charge increases with increasing concentrations of Mg²⁺ in solution or when the outer polycation layer is deposited from a solution of high ionic strength.     

Polyethyleneimine-bonded phases in the separation of proteins by capillary electrophoresis

A hydrophilic, positively charged, durable coating has been developed for capillary electrophoresis of macromolecules. Polyethyleneimine is adsorbed to the inner wall of fused silica capillaries and the adsorbed coating cross-linked into a stable layer. Capillaries of polyethyleneimine-coated silica gave unique separations owing to the reversal of electro-osmotic flow caused by the positively charged coating. The resulting coating was stable from pH 2-12 and could be used over a wide pH range without substantial change in electro-osmotic flow. High-molecular-weight polymers were needed to give thick coatings which mask silanol groups on the wall. Proteins were resolved quickly and efficiently with good recovery using capillaries of 50 cm in length.     

Asymmetric layer-by-layer polyelectrolyte nanofiltration membranes with tunable retention

Nanofiltration (NF) membrane processes are attractive to remove multivalent ions. As ion retention in NF membranes is determined by both size and charge exclusion, negatively charged membranes are required to reject negatively charged ions. Layer-by-layer assembly of alternating polycation (PC) and polyanion layers on top of a support is a versatile method to produce membranes. Especially the polyelectrolyte (PE) couple polydiallyldimethylammoniumchloride and poly(sodium-4-styrenesulfonate) (PDADMAC/PSS) is extensively investigated. This PE couple cannot form highly negatively charged membrane surfaces, due to interdiffusion and charge overcompensation of PDADMAC into the PSS layers, which limits the operational window to tailor membrane properties. We propose the use of asymmetric layer formation and show how combining two charge densities of one PC can produce negatively charged NF membranes. Starting from hollow fiber ultrafiltration supports coated with base layers of PDADMAC/PSS, they are coated with PDADMAC/PSS or poly(acrylamide-co-diallyldimethylammoniumchloride), P(AM-co-DADMAC)/PSS layers. P(AM-co-DADMAC) has a charge density of only 32% compared to 100% for PDADMAC. The particular novel membranes coated with P(AM-co-DADMAC) have a highly negatively charged surface and high permeabilities (7–19 L/[m²hbar]), with high retentions for Na₂SO₄ of up to 95%. These values position the developed membranes in the top range compared to commercial and other layer-by-layer membranes.     

Influence of polyelectrolyte capillary coating conditions on protein analysis in CE

CE of biomolecules is limited by analyte adsorption on the capillary wall. To prevent this, monolayer or successive multiple ionic‐polymer layers (SMILs) of highly charged polyelectrolytes can be physically adsorbed on the inner capillary surface. Although these coatings have become commonly used in CE, no systematic investigation of their performance under different coating conditions has been carried out so far. In a previous study (Nehmé, R., Perrin, C., Cottet, H., Blanchin, M. D., Fabre, H., Electrophoresis 2008, 29, 3013–3023), we investigated the influence of different experimental parameters on coating stability, repeatability and peptide peak efficiency. Optimal coating conditions for monolayer and multilayer (SMILs) poly(diallyldimethylammonium) chloride/ poly(sodium 4‐styrenesulfonate) coated capillaries were determined. In this study, the influence of polyelectrolyte concentration and ionic strength of the coating solutions, and the number of coating layers on coating stability and performance in limiting protein adsorption was carried out. EOF magnitude and repeatability were used to monitor coating stability. Coating ability to limit protein adsorption was investigated by monitoring variations of migration times, time‐corrected peak areas and separation efficiency of test proteins. The separation performance of polyelectrolyte coatings were compared with those obtained with bare silica capillaries.     

Thermal behavior of polyelectrolyte multilayer microcapsules: 2. Insight into molecular mechanisms for the PDADMAC/PSS system

Polyelectrolyte multilayer capsules consisting of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(styrene sulfonate) (PSS) were used as a model system to study the temperature-dependent behavior of polyelectrolyte multilayer films in aqueous media. Shells terminated with PSS shrink upon heating, whereas PDADMAC-terminated ones swell, independent of the nature of the first layer, as measured by means of confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Elemental analysis shows that the initial exponential layer growth of the film leads to a nearly neutral overall charge in the first case or a high positive excess charge in the latter. Depending on this overall charge either surface tension, due to an unfavorable polymer-solvent interaction, or electrostatics dominates, resulting in a shrinkage or expansion of capsules, respectively. Thus, it is possible to swell temperature-shrunk capsules by coating them with an additional PDADMAC layer. Micro-DSC measurements prove that polyelectrolyte multilayers undergo a glass transition in water at which the wall material softens, allowing the rearrangements to occur. It is found that the thermal history has an influence on the temperature behavior of capsules, especially on those ones terminated with PDADMAC. Also, the molecular weight of the polyelectrolytes affects the rearrangement of capsules. The lower the molecular weight and thus the smaller the entanglement of chains, the easier polyelectrolytes can rearrange.     

Influence of polyelectrolyte multilayer adsorption on the temperature sensitivity of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) (PNiPAM) microgels

The electrophoretic mobility and temperature-dependent particle size of poly(N-isopropylacrylamide) (PNiPAM) microgels after alternating adsorption of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS) have been determined. First a PNiPAM-co-acrylic acid (AAc) shell was added to the PNiPAM microgel, then PDADMAC and PSS were adsorbed alternately. The studies of the electrophoretic mobility revealed charge reversal when a polyelectrolyte (PE) layer was adsorbed. Particle size measurements revealed a strong influence of polyelectrolyte adsorption on the temperature-dependent particle swelling. The strong influence of the adsorbed polyelectrolyte on the particle size is in contrast to polyelectrolyte multilayer adsorption on rigid particles.     

Vesicles as pseudostationary phase for enantiomer separation by capillary electrophoresis

The suitability of noncovalently bilayer-coated capillaries for the analysis of proteins by capillary electrophoresis (CE) at medium pH was investigated. Fused-silica capillaries were coated simply by successively flushing with a polybrene (PB) and a poly(vinyl sulfonate) (PVS) solution. A protein test mixture was used to evaluate the performance of the coated capillaries. Comparisons with bare fused-silica capillaries were made. Several background electrolytes (BGEs) were tested in combination with the PB-PVS coating, showing that optimum performance was obtained for the proteins using high BGE concentrations. With a 300 mM Tris phosphate buffer (pH 7.0), good plate numbers (150,000-300,000), symmetrical peaks, and favorable migration-time repeatabilities (RSDs below 0.8%) were obtained for the proteins. Using bare fused-silica capillaries, the protein peaks were significantly broadened and the migration-time RSDs often exceeded 5%. It is concluded that the PB-PVS coating effectively minimizes adverse protein adsorption and provides a very stable electroosmotic flow (EOF). We also investigated the potential of a commercially available bilayer coating (CEofix) for protein analysis. It is demonstrated that with this coating, good plate numbers and peak symmetries for proteins can be achieved when the CEofix BGE ("accelerator") is replaced by a common BGE such as sodium or Tris phosphate. Apparently, the negatively charged polymer present in the "accelerator" interacts with the proteins causing band broadening. The utility of the bilayer coatings is further illustrated by the separation of proteins such as interferon-alpha 2b, myoglobin and carbonic anhydrase, by the analysis of a degraded insulin sample in time, and by the profiling of the glycoprotein ovalbumin. In addition, it is demonstrated that even in the presence of concentrations of human serum albumin in the sample of up to 60 mg/mL, the PB-PVS coating still provides reproducible protein separations of good performance.     

Encapsulation of Organic Pigment Particles with Silica via Sol-Gel Process

This paper presented a novel preparation method of silica coated organic pigment. In this approach, the surfaces of the organic pigment were first orderly modified by poly(sodium 4-styrenesulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC), then coated by silica via sol-gel process of tetraethylorthosilicate (TEOS). The results showed that PVP, pH value, water and TEOS contents had significant influence on the morphology of the silica encapsulated organic pigment. Organic pigments coated silica by this approach could scatter UV ray with wavelength less than 270 nm, and this scattering property increased with more silica coated.