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PubMed2003

Thin films of polyelectrolyte-encapsulated catalase microcrystals for biosensing.

Polyelectrolyte (PE)-encapsulated catalase microcrystals were assembled onto gold electrodes by their sequential deposition with oppositely charged PEs, utilizing electrostatic interactions to form enzyme thin films for biosensing. The PE coating around the microcrystals provided a regular surface charge, thus facilitating the stepwise film growth, and it effectively prevented catalase leakage from the assembled films. The encapsulated catalase was shown to retain both its biological and its electrochemical activity. Direct electron transfer between catalase molecules and the gold electrode was achieved without the aid of any electron mediator. In pH 5.0 phosphate buffer solution, the apparent formal potential (E(o)') of catalase was -0.131 V (vs Ag/AgCl). As a H2O2 biosensor, films consisting of one layer of the encapsulated catalase displayed considerably higher (approximately 5-fold) and more stable electrocatalytic responses to the reduction of H2O2 than did corresponding films made of one layer of nonencapsulated catalase or solubilized catalase. An increase in either the number of "precursor" PE layers between the gold electrodes and the catalase microcrystal layers in the film or the number of PE layers encapsulating the catalase microcrystals was found to decrease the electrocatalytic activity of the electrode. At low precursor PE layer numbers (approximately 2) and PE encapsulating layers (approximately 4), the current response was proportional to the H2O2 concentration in the range 3.0 x 10(-6) to 1.0 x 10(-2) M. The overall electroactivity of the multilayer film increased for the first two layers of encapsulated catalase, after which a plateau was observed. This was attributed to the increasing difficulty of electron transfer and substrate diffusion limitations. The current approach of using immobilized PE-encapsulated enzyme microcrystals for biosensing provides a versatile method to prepare high enzyme content films with high and tailored enzyme activities.

Biosensing Techniques↗
PubMed2003

Chiral separations using polymeric surfactants and polyelectrolyte multilayers in open-tubular capillary electrochromatography.

In this study, fused-silica capillaries are modified using a polyelectrolyte multilayer (PEM) coating procedure in open-tubular capillary electrochromatography. The PEM coating was constructed in situ with alternating rinses of positively and negatively charged polymers. The quaternary ammonium salt poly (diallyldimethylammonium chloride) was used as the cationic polymer, and the polymeric surfactant poly (sodium N-undecanoyl-l-leucylvalinate) was used as the anionic polymer. Previous studies have shown that the PEM-coated capillaries used for achiral separations have excellent reproducibilities and high stabilities against extreme pH values. In the current study, this PEM coating approach was applied to chiral separations of 1,1'-binaphthyl-2,2'-dihydrogenphosphate (BNP), 1,1'-bi-2-naphthol, secobarbital, pentobarbital, and temazepam. However, the PEM coating procedure used in the achiral studies needed to be significantly modified in order to achieve chiral separations. Optimal conditions were established by varying the additives (sodium chloride, 1-ethyl-3-methyl-1H-imidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate) in the polymer deposition solutions, the salt concentration, the column temperature, and the bilayer number. Reproducibilities were evaluated by use of the relative standard deviation (RSD) values of the electroosmotic flow (EOF) and the first peak ((R)-(+)-BNP). In all cases, the run-to-run and capillary-to-capillary RSD values of EOF were less than 0.5%, and the run-to-run RSD values of the (R)-(+)-BNP peak were less than 1%. In addition, more than 230 runs were performed on a single PEM-coated capillary.

Journal Article↗
PubMed2003

Effect of polyelectrolyte multilayers on the response of a quartz crystal microbalance.

The effect of a polyelectrolyte (PE) multilayers made by a layer-by-layer technique on the response of a quartz crystal microbalance (QCM) is studied by using novel mathematical methods based on the Möbius transformations and their matrix representations in the complex plane. In the first method, the basic properties of the Möbius transformation are used for obtaining the PE bilayer matrix from the QCM impedance measurements taken at four different numbers of layers. In the second method, nonlinear fitting with concomitant error estimation is used for obtaining the elements of the bilayer matrix. The methods are applied to a multilayer composed of 150 bilayers of poly(sodium 4-styrenesulfonate) and poly(diallyldimethylammonium) chloride on a quartz crystal resonator. The structure of the system is discussed, and the bulk acoustic impedance and areal mass density of the bilayer are calculated from the layer matrix.

Journal Article↗
PubMed2005

Cytometry and velocimetry on a microfluidic chip using polyelectrolytic salt bridges.

This paper reports a polyelectrolytic salt bridge-based electrode (PSBE), which is a key embedded unit in a microchip device that can size-selectively count microparticles and measure their velocities. The construction of salt bridges at specific locations within a microfluidic chip enables dc-driven electrical detection to be performed successfully. This is expected to be a competitive alternative to the optical methods currently used in conventional cell sorters. The PSBEs were fabricated by irradiating ultraviolet light over a patterned mask on the parts of interest, which were filled with an aqueous monomer solution containing diallyldimethylammonium chloride. A pair of such PSBEs was easily formed at the two lateral branches perpendicular to the main microchannel and was found to be very useful for dc impedometry. The human blood cells as well as the fluorescent microbeads passing between the two PSBEs produced impedance signals in proportional to their size. The information about the velocity of a microparticle was extracted from a doublet of the dc impedance signals, which were generated when cells or microbeads sequentially passed through two PSBE pairs separated from each other by a fixed distance. The plot of peak amplitude versus velocity of the moving microbeads and cells indicated only a slight correlation between the size and the velocity, which means that the peak amplitude of the dc impedance signals alone can provide information about the size of the cells in a mixture. The experimental results showed a screening rate of over 1000 cells s(-1) and a velocity of the cells of over 100 mm s(-1). Compared with the previously suggested electrical detection system based on metal electrodes, the sensitivity and selectivity in cell detection were remarkably improved. In addition, the detection unit including the operating circuit became innovatively simple and the whole device could be miniaturized.

Blood Cell Count↗
PubMed2006

Synthesis of a polyelectrolyte and its applications in laser desorption/ionization.

A novel laser energy-absorbing polymer derivatized from an energy-absorbing molecule has been synthesized. This polymer effectively eliminates the matrix addition step and the use of requisite small organic chemical matrixes from MALDI. The resulting polyelectrolyte-assisted laser desorption/ionization method has been proven to have some exceptional advantages over current MALDI methods. First, the matrix addition step from the LDI analytical process was eliminated. Second, the low molecular weight signal from energy-absorbing molecules was minimized by covalently linking the energy-absorbing molecules to the backbone of the polymer and other ionization-enhancing pendant groups on the backbone. Finally, the mass resolution of LDI was enhanced by minimizing chemical background noise throughout the spectrum. Polymeric linkage of energy-absorbing molecules aligns them with each other in an ordered structure, similar to MALDI matrix crystallization. Using the designed polymer film, laser desorption/ionization for proteins and peptides were successfully performed without the addition of any matrix. Analytical results for the synthesized monomer and polymers will be also presented.

Journal Article↗
PubMed2006

Use of porous membranes modified with polyelectrolyte multilayers as substrates for protein arrays with low nonspecific adsorption.

Coating of substrates with polyelectrolyte multilayers terminated with poly(acrylic acid) (PAA) followed by activation of the free -COOH groups of PAA provides a surface that readily reacts with amine groups to allow covalent immobilization of antibodies. The use of this procedure to prepare arrays of antibodies in porous alumina supports facilitates construction of a flow-through system for analysis of fluorescently labeled antigens. Detection limits in the analysis of Cy5-labeled IgG are 0.02 ng/mL because of the high surface area of the alumina membrane, and the minimal diameter of the substrate pores results in binding limited by kinetics, not mass transport. Moreover, PAA-terminated films resist nonspecific protein adsorption, so blocking of antibody arrays with bovine serum albumin is not necessary. These microarrays are capable of effective analysis in 10% fetal bovine serum.

Acrylic Resins↗
PubMed2006

Electrogenerated chemiluminescence in polyelectrolyte multilayers: efficiency and mechanism.

The presence of an ultrathin film of polyelectrolyte complex, formed by the multilayering method, on an electrode was shown to enhance the intensity of electrogenerated chemiluminescence (ECL) from the tris(2,2')bipyridylruthenium(II)/tripropylamine system. Platinum electrodes coated with up to 17 layers of poly(diallyldimethylammonium chloride) or poly(vinylmethylpyridine), alternately layered with poly(styrenesulfonate), revealed significant differences in enhancement of ECL, depending on the identity of the multilayer. ECL following deposition of each layer showed an oscillating intensity of light emission, which alludes to the importance of surface and bulk charge. This effect, along with others, such as increased output with increasing tripropylamine concentration, was used to suggest a mechanism for enhanced ECL intensity at multilayer-coated electrodes.

Journal Article↗
PubMed2006

Approaches to quantifying and visualizing polyelectrolyte multilayer film formation on particles.

Colloidal particles prepared by using the layer-by-layer technique are increasingly finding application in diagnostics, drug delivery, and sensing. Herein, we outline methods for applying three established techniques, confocal laser scanning microscopy (CLSM), flow cytometry, and differential interference contrast (DIC) microscopy, to characterize ultrathin films of poly(styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) assembled on silica particles. Both CLSM and flow cytometry require the use of fluorescently labeled polyelectrolytes (PEs). The film homogeneity can be assessed using CLSM, while flow cytometry allows analysis at unparalleled speed (thousands of particles per second) with unprecedented sensitivity (<0.5 fg of adsorbed polymer) of polydispersed particles of different size ( approximately 300 nm to tens of micrometers). Using CLSM and flow cytometry measurements, in conjunction with quartz crystal microgravimetry measurements on planar supports, allows quantification of PSS/PAH layer buildup on the particles. Furthermore, flow cytometry and DIC microscopy were used to unequivocally distinguish between silica-core PSS/PAH-shell particles and hollow PSS/PAH capsules obtained following core removal. The techniques outlined here are not limited to measuring PE deposition on solid particles but, in principle, are equally applicable to quantifying the adsorption of other materials (such as DNA, proteins, or nanoparticles) on a variety of particulate systems, including hollow capsules, emulsions, and cells.

Journal Article↗
PubMed2005

Conjugated polyelectrolytes: conformation-sensitive optical probes for detection of amyloid fibril formation.

The in vivo deposition of amyloid fibrils is a hallmark of many devastating diseases known as the amyloidoses. Amyloid formation in vitro may also complicate production of proteins in the biotechnology industry. Simple, sensitive, and versatile tools that detect the fibrillar conformation of amyloidogenic proteins are thus of great importance. We have developed a negatively charged conjugated polyelectrolyte that displays different characteristic optical changes, detected visually or by absorption and emission, depending on whether the protein with which it forms a complex is in its native state or amyloid fibril conformation. This simple, rapid, and novel methodology was applied here to two amyloidogenic proteins, insulin and lysozyme, and its validity for detection of their fibrillar conformation was verified by currently used methods such as circular dichroism, transmission electron microscopy, and Congo red absorption.

Acetates↗
PubMed1996

Polyelectrolyte counterion condensation theory explains differential scanning calorimetry studies of salt-induced condensation of chicken erythrocyte chromatin.

The salt-induced chromatin condensation in chicken erythrocyte nuclei is studied by differential scanning calorimetry (DSC). The degree of chromatin condensation is measured for condensation induced by monovalent, divalent, trivalent, or tetravalent cations and by a mixture of sodium and magnesium. These last two cations show an evident competition effect. Salt-induced chromatin condensation is shown to be an entropy-driven process. A simple model of chromatin based on the polyelectrolyte counterion condensation theory is used in order to compute the charge neutralized by the cations in each chromatin domain. The degree of chromatin condensation is shown to be related to the weighed sum of the square of the phosphate charge of each domain. The model predicts the salt and the chromatin concentration dependence of the condensation and the effect of H1 removal.

Animals↗
PubMed1997

Opposite effects of electrostatics and steric exclusion on bundle formation by F-actin and other filamentous polyelectrolytes.

A number of positively charged polypeptides and proteins bundle DNA, F-actin, microtubules, and viruses such as filamentous phage fd and tobacco mosaic virus (TMV), as well as intermediate filaments formed by vimentin. The general behavior is dictated by the common polyelectrolyte nature of these biopolymers, which gives rise to nonspecific binding by ligands carrying several net opposite charges. An attractive interaction accounts for the subsequent lateral aggregation, distinguishing this transition from the liquid crystalline formation of filamentous particles at high concentrations. Morphologically similar filament bundles can also be induced by inert solutes such as polyethylene glycol (PEG) and proteins that do not bind the macromolecular filaments, but the physicochemistry underlying this class of bundle transitions is distinct. In particular, bundling transitions induced by electrostatic and steric mechanisms have an opposite dependence on the solution ionic strength and the concentration of the filamentous biopolymers. The distinct mechanisms illustrated in this report may each contribute to the formation of specific polymer bundles under physiological conditions.

Actins↗
PubMed2001

Fluorescence study of Cu(2+)-induced interaction between albumin and anionic polyelectrolytes.

The Cu(2+)-induced complex formation of bovine serum albumin (BSA) with anionic polyelectrolytes (PEs) (polyacrylic acid (PAA), poly(N-isopropylacrylamide) [poly[NIPAAm]], and copolymers of N-isopropylacrylamide (NIPAAm) and acrylic acid) in aqueous solution was studied by a fluorescence technique and high-performance liquid chromatography analysis. The character of the interactions depends on the monomer composition (r = [COOH]/[NIPAAm]), [Cu(2+)]/[PE], and [BSA]/[PE] ratios and solution pH. Two types of ternary polycomplex (polymer + Cu(2+) + BSA) particles are formed depending on the monomer composition r of the copolymer. At r from 1/3 to 1/1, the protein molecules in the structure of ternary polycomplex particles are densely covered by the shell of a polymer coil and practically "fenced off" from the water environment. At r > or = 3/1 ternary polycomplex PAA-Cu(2+)-BSA particles have more friable structures in which protein molecules are practically exposed to the solution. At low polymer concentration, an intrapolymer ternary polycomplex is formed. This complex aggregates to an interpolymer species upon increase in polymer concentration. Fluorescence data indicate that in ternary complex polymer interacts through Cu(2+) ions with BSA preferentially at the site close to the location of "cleft" tryptophan residue. This leads to static quenching of this tryptophan fluorescence. Cu(2+)-induced complex formation is an equilibrium reaction.

Animals↗
PubMed2000

Protein interactions with polyelectrolyte multilayers: interactions between human serum albumin and polystyrene sulfonate/polyallylamine multilayers.

The interactions between polystyrenesulfonate (PSS)/polyallylamine (PAH) multilayers with human serum albumin (HSA) were investigated by means of scanning angle reflectometry (SAR). We find that albumin adsorbs both on multilayers terminating with PSS (negatively charged) or PAH (positively charged) polyelectrolytes. On films terminating with PSS only, an albumin equivalent monolayer is found whereas when PAH constitutes the outer layer, albumin interacts with the multilayer in such a way as to form a protein film that extends over thicknesses that can be as high as four times the largest dimension of the native albumin molecule. Once the protein film is formed, it is found that when the albumin solution is replaced by a pure buffer solution of same ionic strength as the adsorption solution almost no desorption takes place. On the other hand, when a buffer solution of higher ionic strength is brought in contact with the albumin film, a significant amount of adsorbed proteins is released. One also observes that, for albumin solutions of a given protein concentration, the adsorbed protein amount depends on the ionic strength of the adsorption solution. On surfaces terminating with PAH, the adsorbed protein amount first increases rapidly but passes through a maximum and decreases with the ionic strength. The ionic strength corresponding to the maximum of the adsorbed albumin amount itself depends on the albumin concentration. On the other hand, on films terminating with PSS the adsorbed amount increases with the salt concentration before leveling-off. These results show that the underlying complexity of concentration and pH dependent adsorption/desorption equilibria often simply termed "protein adsorption" is the result of antagonist competing interactions that are mainly of electrostatic origin. We also propose two microscopic models, that are compatible with our experimental observations.

Adsorption↗
PubMed2001

Orientation of alpha-helical poly(L-lysine) in consecutively adsorbed polyelectrolyte multilayers on texturized silicon substrates.

Alternate polyelectrolyte multilayers composed of poly(L-lysine) (PLL) in the alpha-helical state and poly(maleic acid-co-alpha-methylstyrene) (PMA-MS) were deposited by consecutively adsorbing from aqueous solutions on both unmodified and unidirectionally scratched silicon substrates. Thereby, the alpha-helical PLL rods formed in the presence of NaClO(4) were found to be significantly aligned along the scratching direction of the substrate. From the dichroic ratios of the amide I and amide II band, obtained by ATR-FTIR spectroscopy, order parameters with respect to uniaxial orientation were determined using a cone distribution model and the known angles of the transition dipole moments relative to the helix axis. They ranged from S = 0.5-0.7 for the PLL rods oriented on the texturized Si substrate and S = 0.0-0.2 (S = 1 for perfect ordering) for the unoriented PLL rods in the dry and wet states, respectively. Additionally, multilayers composed of PLL and poly(vinyl sulfate) showed similar uniaxial alignment on texturized Si substrates (S = 0.6). Generally, drying the multilayers caused a certain loss of order. Surfaces of anisotropically oriented alpha-helical polypeptides could be interesting for biomimetic purposes.

Adsorption↗
PubMedDate not supplied

Rational design of cytophilic and cytophobic polyelectrolyte multilayer thin films.

Nanostructured polyelectrolyte multilayer thin films electrostatically assembled alternately from such polymers as poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) were investigated for their in vitro cell interactions. Not surprisingly, NR6WT cells, a highly adhesive murine fibroblast cell line, attached to many different multilayer combinations tested. However, PAH/PAA multilayers constructed at pH deposition conditions of 2.0/2.0 were completely bioinert. Analogous cell interactions were observed with PAH/poly(methacrylic acid) (PAH/PMA), PAH/sulfonated poly(styrene) (PAH/SPS), and poly(diallyldimethylammonium chloride)/SPS (PDAC/SPS) systems, thereby suggesting a general trend in the fibroblasts' response to multilayers. Specifically, highly ionically stitched films attracted cells, whereas weakly ionically cross-linked multilayers, which swell substantially in physiological conditions to present richly hydrated surfaces, resisted fibroblast attachment. Thus, by manipulating the multilayer pH or ionic strength assembly conditions or both, which in turn dictate the molecular architecture of the thin films, one may powerfully direct a single multilayer combination to be either cell adhesive or cell resistant.

Acrylic Resins↗
PubMedDate not supplied

Site-selective lateral multilayer assembly of bienzyme with polyelectrolyte on ITO electrode based on electric field-induced directly layer-by-layer deposition.

We describe here a new approach to construct a multilayer enzyme/polyelectrolyte film on a structured transparent indium-tin oxide (ITO) covered glass electrode surface as micropattern, on which two different types of enzyme distributed laterally on one common substrate without interference. The multilayer film was prepared by alternate electric field directed layer-by-layer assembly deposition and alternate deposition of different redox enzymes and polyelectrolyte poly(diallyldimethylammonium chloride) (PDDA) onto the site-selective ITO glass electrode surface. The cyclic voltammogram, obtained from the ITO glass electrode modified with the glucose oxidase (GO(X))/PDDA and catalase (CA(T))/PDDA multilayers, revealed that the bioelectrocatalytic response is directly correlated to the number of deposition bilayers. From the analysis of cyclic voltammetric characterization, the coverage of catalytically active enzymes per enzyme/PDDA bilayer during the multilayer formation was homogeneous, which demonstrates that the multilayer is constructed in a spatially ordered manner. Also, from the atomic force microscopy and Brewster angle microscopy measurements, more information of the multilayer constructed by different methods on the modified electrode surface is obtained and compared. This fabrication technique is simple and would be applicable to the construction of a thickness- and area-controlled biopattern composed of multi-enzymes as well as multiple biomaterials.

Biosensing Techniques↗
PubMedDate not supplied

New class of ultrathin, highly cell-adhesion-resistant polyelectrolyte multilayers with micropatterning capabilities.

Hydrogen-bonded multilayers comprised of polyacrylamide (PAAm) and a weak polyelectrolyte, such as poly(acrylic acid) (PAA) or poly(methacrylic acid) (PMA), were investigated for their surface-cell interactions. The assembled films were lightly cross-linked thermally or photochemically in order to render them stable in a physiological environment. Both PAA/PAAm and PMA/PAAm multilayers were found to exhibit a high resistance to the adhesion (cytophobicity) of mammalian fibroblasts, even with only a single bilayer coating. Protein adsorption to the multilayers, as revealed by surface plasmon resonance measurements, was greatly reduced for fibronectin and serum-containing medium. In situ swelling experiments indicate that the H-bonded multilayers are hydrogellike coatings capable of a high level of swelling in buffered solution. Utilizing the H-bonding nature of these multilayers, we were able to micropattern the films to create more complex cell-resistant/-adhesive surfaces. The long-term stability of the cell-resistant multilayers was found to be exceptionally good even under conditions (pH 7.4, buffered solution) where a high degree of swelling takes place. No degradation of the micropatterned films was observed over a period of a month, during which time the multilayer coatings remained highly resistant to cell-adhesion.

Acrylic Resins↗
PubMedDate not supplied

Incorporation of alkaline phosphatase into layer-by-layer polyelectrolyte films on the surface of affi-gel heparin beads: physicochemical characterization and evaluation of the enzyme stability.

The preparation of functionalized beads in the micrometer size range that can be used to probe the action of immobilized biomolecules on cell cultures during controlled periods of time is of fundamental importance in cell biology. However, the preparation and characterization of such particles is tedious because of their fast sedimentation. It is hence difficult to prepare such beads in a reproducible manner. This highlights the need to prepare an important batch of functionnalized particles and to store them under conditions where the loss of biological activity is minimized. The aim of this paper was to immobilize alkaline phosphatase (AP) as a model enzyme on the surface of Affi-gel heparin beads functionnalized by means of a layer-by-layer (LBL) film made of poly-l-glutamic (PGA) acid and poly-l-lysine (PLL). The enzyme has been adsorbed either on the top of the LBL film or embedded under five polyelectrolyte layers. When embedded, the enzyme was not released in buffer and retained more than 30% of its initial activity after 3 months of storage at 4 degrees C. However, when the enzyme was adsorbed on top of the LBL film, about 80% of the adsorbed enzyme was released in the buffer after a few days of storage. Longer storage did not lead to any further desorption and the remaining enzyme displayed the same evolution of its activity with time as the embedded enzyme. The time evolution of the enzyme activity on the beads is compared with that in solution alone and in the presence of PGA and PLL separately.

Alkaline Phosphatase↗