Biomedical subjects

R Hidalgo-Alvarez

Publications and source records attributed to R Hidalgo-Alvarez.

18 recordsLinked to original sources

PubMed2002

Constant bond breakup probability model for reversible aggregation processes.

Reversible aggregation processes were simulated for systems of freely diffusing sticky particles. Reversibility was introduced by allowing that all bonds in the system may break with a given probability per time interval. In order to describe the kinetics of such aggregation-fragmentation processes, a fragmentation kernel was developed and then used together with the Brownian aggregation kernel for solving the corresponding kinetic master equation. The deduced fragmentation kernel considers a single characteristic lifetime for all bonds and accounts for the cluster morphology by averaging over all possible configurations for clusters of a given size. It became evident that the simulated cluster-size distributions could be described only when an additional fragmentation effectiveness was considered. Doing so, the stochastic solutions were in good agreement with the simulated data.

Journal Article↗

PubMed2002

Interaction potentials, structural ordering and effective charges in dispersions of charged colloidal particles.

As colloidal dispersions of charged particles exhibit a wide variety of commercial, technological and scientific applications, a considerable theoretical effort has been devoted to finding an effective interaction potential from primitive models. The forces derived from this potential should justify the spatial ordering experimentally observed under certain conditions. This paper reviews the advances in these theoretical studies as well as some experiments (based on the mentioned order) that try to corroborate them. Special attention has been paid to the Derjaguin-Landau-Verwey-Overbeek (DLVO) potential. Nowadays, many of these theoretical investigations suggest that it could be applied if some of its parameters are renormalized. Nevertheless, to achieve a renormalization procedure in a strict way (from a primitive model) is a difficult task as a result of the size and charge asymmetries between small ions and macroions. Thus, several procedures for computing renormalized charges in a simple way have been developed. However, the notion of effective charge has also been widely used (as a adjustable parameter) in order to justify results found for several kinds of colloids (like solid particle dispersions or micellar systems) by means of quite different experimental techniques. Renormalization (as well as ion condensation) approaches, experiments and the controversial relationship between theoretical and phenomenological effective charges are also reviewed in this work.

Journal Article↗

PubMed2001

Specific cation adsorption on protein-covered particles and its influence on colloidal stability.

Protein coated particles present an anomalous colloidal stability at high ionic strength when the classical theory (DLVO) predicts aggregation. This observed deviation from DLVO behaviour appears for electrolyte concentrations above some critical bulk value. As we have suggested in previous publications the existence of an additional short-range repulsive 'hydration force' due to specific hydrated cation adsorption could explain this anomalous stability. The overlap of the hydration layers when two particles approach should provoke this repulsive force. New evidence of this mechanism has been observed when electrophoretic mobilities of protein-carrying latex particles were measured at various concentrations of sodium and calcium chloride. In the latter case a sign reversal of zeta-potential was found, probably due to the specific adsorption of Ca(2+) ions on protein molecules. The adsorption increases with the medium pH. These results have been analyzed following the treatment proposed by Ohshima and co-workers for large charged colloidal particles coated with a layer of protein. This study shows an increase in the positive fixed-charge density on the protein caused by the adsorption of cations.

Journal Article↗

PubMed2000

Ionic condensation theories and the liquidlike structures observed in colloidal dispersions

Though the notion of effective charge has been widely used to fit experimental data, the possibility of predicting this adjustable parameter through a model remains unclear. A likely reason for this is the complexity involved in the theoretical approaches in the case of fluids with large asymmetries between their components. This paper deals with several condensation theories for spherical colloids, developed to provide effective charge values from simple models. Liquidlike structures are formed in colloidal dispersions for a set of latexes with different properties (charge, size, and polymeric composition). Effective charges are determined from experimental structure factors using a Derjaguin-Landau-Verwey-Overbeek potential and an Ornstein-Zernike scheme. The numerical coincidence between effective and post-condensation charges is fairly acceptable only for latexes with small size and charge. A simple approach based on the Manning condensation theory for linear polyelectrolytes is also discussed.

Journal Article↗

PubMed2000

Multiple contact kernel for diffusionlike aggregation

The Brownian kernel is usually assumed to describe pure diffusion-limited cluster-aggregation processes. In this work, we show that this assumption is correct for simulated data. For experimental data, however, significant deviations were observed although the system was aggregated at an electrolyte concentration well above the critical coagulation concentration. This indicates that residual cluster-cluster interactions are not completely absent in real experimental systems. In order to improve the description of the experimental data, we developed a kernel that considers a monomer-monomer sticking probability explicitly and accounts for the possibility of multiple monomer-monomer contacts in the cluster collision area. The proposed kernel agrees excellently with the experimental cluster-size distribution and the corresponding scaling function.

Journal Article↗

PubMed2000

A comparative study between the adsorption of IgY and IgG on latex particles.

The use of egg yolk antibodies (IgY) instead of IgG from mammalian species may present several advantages in the development of routine diagnostic immunoassays. On the one hand, the animal suffering is reduced, as antibodies are obtained directly from the egg. On the other hand, the use of IgY avoids the rheumatoid factor interference. The rheumatoid factor interacts with IgG molecules in many immunoassays causing false positive results. Despite these advantages, IgY antibodies are scarcely used. As part of an aim to develop a diagnostic test based on IgY-latex agglutination, a preliminary study on some characteristics of the IgY-latex complexes is carried out. In this work, protein adsorption and desorption, isoelectric point, electrokinetic mobility, and colloidal stability are analysed. Results are compared to those obtained by IgG. Interesting differences are observed (which mainly arise from the difference in molecular structure between IgY and IgG), suggesting that IgY is a more hydrophobic molecule than IgG. In addition, colloidal dispersions of IgY-covered latex particles are more stable (at pH 8) than those sensitized by IgG.

Adsorption↗

PubMed1999

Forces acting on particle-enhanced immunoassays.

The aim of the present work is to study the role of the different forces involved in the agglutination of immuno gamma-globulin (IgG) covered latex particles due to antigen-antibody reaction. An experimental investigation on the adsorption of IgG molecules on three latexes with different surface charge densities is described. Photon correlation spectroscopy was used to determine the hydrodynamic layer thickness of the IgG molecules adsorbed on the latexes. In order to get an insight into the forces acting between two antibody-covered particles approaching each other, the colloidal stability and immunoreactivity of these biocomplexes were studied. They can be stabilized by electrostatic or hydration forces. The immunological agglutination of IgG-immobilized latex particles due to the addition of the antigen was quantified through scattered light intensity measurements. The immunoresponse increases with ionic strength of the medium until a maximum value is achieved. Above this maximum, the immunoreactivity decreases.

Adsorption↗

PubMed1998

Particle enhanced immunoassays stabilized by hydration forces: a comparative study between IgG and F(ab)2 immunoreactivity.

In previous publications we have discussed the stabilization mechanism of hydration forces as applied to the development of latex agglutination tests. We describe here how we have obtained stable and reactive IgG-latex conjugates in a high-ionic-strength reaction buffer. To this end we have made agglutination tests with polystyrene beads sensitized with IgG, measuring the immunoaggregation reaction with human C-reactive protein in a stopped-flow nephelometer. The results are compared to those obtained with a F(ab')2-latex conjugate with similar antibody molecule coverage. Adsorption isotherms of F(ab')2 and IgG on latex at pH 7.2 were obtained to study the affinity of these antibodies for the surface. The results of the electrokinetic characterization of the antibody-latex conjugates agree satisfactorily with those obtained from stability studies. This research throws light upon the use of hydration forces as a new approach to stabilizing immunoassay reagents that are colloidally unstable in physiological reaction buffers.

Adsorption↗

PubMed1998

Modelling the kinetics of antigen-antibody reactions at particle enhanced optical immunoassays.

Functionalized latexes coated by antibodies are used in diagnostic tests for the detection of antigens in biological fluids. A simple kinetic model is presented which is related to the optical monitoring of the formation of specific complexes between antigen and antibody amplified by latex beads. The antibodies are chemically coupled onto chloromethylstyrene (CMST) particles. The kinetic model is able to describe the immunoprecipitin curves of immunolatex beads. The number of fitting parameters is relatively reduced (only three), and the meaning of these parameters can be interpreted in terms of the chemical equilibrium constant, the percentage of active IgG on the latex beads, and optical response. The model explains very well the optical response of immunolatex prepared by covalent coupling of antibodies on polymer carriers.

Animals↗

PubMed1998

Latex immunoassays: comparative studies on covalent and physical immobilization of antibodies. I. F(ab')2 fragments.

Colloidal particles coated with antibodies are currently used in diagnostic test systems for the detection of antigens in biological fluids. Immobilization is usually carried out by physical adsorption. Covalent coupling of antibodies to particles, however, offers certain advantages. The present research deals with the study of these possible advantages. A sulphonated polystyrene latex has been used to prepare an immunolatex with physically adsorbed antibodies, while a functionalized latex with chloromethyl groups on the surface has been used for the partly covalent coupling of the antibody (F(ab')2 fragments). The immunoreactivity was studied by measuring the variations in scattered light intensity after mixing a solution of CRP antigen and the sensitized latex. The influence on the immunoresponse of the scattering angle (5, 10, and 20 deg), protein coverage and storage time have been studied for both systems.

Adsorption↗

PubMed1998

Latex immunoassays: comparative studies on covalent and physical immobilization of antibodies. II. IgG.

Latex particles coated with IgG, currently used for immunoassay tests, are not colloidally stable under physiological conditions. Post-treatment of sensitized polystyrene microspheres with different substances (BSA, surfactants) to increase colloidal stability has been often used to solve this problem. We propose the possibility of stabilizing the antibody-latex conjugates by hydration forces at high ionic strength. On the other hand. immobilization of the proteins may be performed either by physical adsorption or by covalent binding to functionalized surface groups. In this second part of these series we have studied the immunoreactivity of IgG antibody partly covalently bound and physically adsorbed, and the results were compared to those obtained with F(ab')2 fragments in Part I.

Adsorption↗

PubMed1997

A comparative study of optical techniques applied to particle-enhanced assays of C-reactive protein.

This work is based on the well-established immunoassay principle of agglutination of latex particles covered by immunoproteins. In our experiments, positively charged particles act as carriers for the F(ab')2 fragment, obtained from rabbit polyclonal IgG, active against C-reactive protein (CRP). The presence of the antigen CRP in the immunolatex system causes agglutination and the aim of the present study was to compare different optical techniques (turbidimetry, nephelometry, angular anisotropy and photon correlation spectroscopy) capable of detecting the agglutination. The sensitivity and detection limit largely depend on the optical method. We have analyzed for each optical technique the following aspects: sensitivity, reproducibility, detection limit, reaction time, amount of sample wasted and availability of the required detection device. The results presented in this paper show that both angular anisotropy and photon correlation spectroscopy offer lower detection limits, and use little reagent, but have longer assay times than the classical optical techniques of turbidimetry and nephelometry.

Animals↗

PubMed1997

Chloroactivated latex particles for covalent coupling of antibodies. Application to immunoassays.

The aim of the present work is to prepare and characterize a functionalized latex with chloromethyl groups on the surface and to perform the covalent coupling of anti-human serum albumin (a-HSA) IgG protein. The chloromethyl-styrene latex (CMS) was synthesized by means of a core-shell emulsion polymerization in a batch reactor. The monodisperse-obtained latex was characterized by determining the diameter (TEM and PCS), the surface charge density (conductometric and potentiometric titration), the amount of chloromethyl groups on the surface (hydrolysis reaction), and the stability vs electrolyte concentration (turbidity measurements). Electrokinetic characterization was also performed (electrophoretic mobility versus pH and ionic strength). IgG was chemically bound to the latex particles under different sensitization and block-stabilization conditions. Colloidal stability of complexes was studied to select an immunolatex suitable for the development of latex immunoassays. The final part of this work consists of a study of the immunoreactivity of the IgG-latex complexes at different pH and ionic strength, in particular under physiological conditions. The results show that chemically bound IgG to chloromethyl latex provides an IgG-latex complex suitable for application in immunodiagnosis tests.

Buffers↗

PubMed1996

Particle enhanced immunoaggregation of F(ab')2 molecules.

The immunological agglutination reactions of physically absorbed F(ab')2 molecules onto anionic and cationic latex particles have been investigated by means of optical absorbance measurements. These measurements have been conducted under different conditions to determine the most influential factors. Surface F(ab')2 and BSA densities, particle concentration in the reaction medium and polyethylene glycol concentration are some of these factors. Sensitized cationic and anionic latexes differ considerably with respect to their colloidal stability and reactivity. As a general rule, the sensitized cationic latex has a relatively higher colloidal stability and hence, it provides reagents with a better optical response. Less than 0.025 microgram/ml of C-reactive protein has been detected using this particle enhanced optical immunoassay.

Adsorption↗

PubMed1995

Coadsorption of IgG and BSA onto sulfonated polystyrene latex: I. Sequential and competitive coadsorption isotherms.

In this work the sequential and competitive coadsorption of IgG and BSA proteins on a sulfonate polystyrene latex with high surface charge density have been studied. For sequential coadsorption the IgG/a-CRP was first adsorbed and then the free surface of the particle was saturated by redispersion of the pellet in a solution with a high concentration of monomeric BSA (m-BSA). The competitive coadsorption experiments were carried out in two separate experiments by changing the initial concentration of one protein when the concentration of other protein was high and constant. During the incubation the pH was 5 or 6, and the ionic strength 2 mM, as in previous studies the adsorption of BSA was very low at neutral or basic pH regardless of the amount of adsorbed IgG. From these coadsorption experiments it was possible to obtain latex-protein complexes with a similar degree of coverage by each protein, high adsorption of IgG and different amounts of BSA, or high adsorption of BSA and a low, but significant, amount of IgG. The latex-protein complexes were electrokinetically characterized by measuring the electrophoretic mobility of each complex vs the pH of redispersion. In that way we can detect the i.e.p. of the complexes and the pH range in which the electrostatic repulsion can make them colloidally stable.

Adsorption↗

PubMed1995

Coadsorption of IgG and BSA onto sulfonated polystyrene latex: II. Colloidal stability and immunoreactivity.

The present work deals with the study of the colloidal stability and immunoreactivity of sulfonated polystyrene latex particles covered by different amounts of m-BSA and IgG/a-CRP. These proteins have been previously adsorbed onto a sulfonated latex by sequential and competitive coadsorption experiments and it was possible to obtain latex-protein particles with different degrees of coverage by each protein. The latex particles, fully or partially covered by each protein (termed latex-protein complexes), were resuspended under several conditions (different pH and ionic strength values) and their colloidal stability, vs the addition of the electrolyte was studied using turbidity measurements. This stability appeared at a high degree of coverage by BSA and at a pH in which the BSA was negatively charged. At a high degree of coverage by IgG, the latex particles were unstable at all pHs. As a final part of this work, the immunoreactivity of several complexes was studied following the changes in the turbidity after the addition of CRP antigen. Only the complexes which were colloidally stable gave detectable reactivity. However, the complexes with a relatively low degree of coverage by IgG/a-CRP gave good immunoreactivity. Therefore, the latex-protein complex properties depended on the percentage of BSA or IgG adsorbed and on the electric state of the proteins at the redispersion pH. Under specific incubation conditions, sulfonated latex covered by significant IgG/BSA percentages was obtained, which showed a high colloidal stability and good immunoreactivity.

Adsorption↗

PubMed1994

The adsorption of F(ab')2 on positively and negatively charged polystyrene beads.

An experimental study on the adsorption of F(ab')2 molecules onto positively and negatively charged polystyrene beads is described. Adsorption isotherms at low ionic strength and different pH were performed. In all cases the adsorption isotherms showed well-defined plateau. The positively charged polystyrene beads showed a higher adsorption of F(ab')2 molecules over a range of pH. This latex sample reached a maximum adsorption at pH 7, whereas the negatively charged sample showed a maximum at pH 5. The isoelectric points of the F(ab')2-PS complexes were around 7.5 and 4.5 respectively. The differences in the colloidal stability of the sensitized beads are not explained by the electrophoretic mobility values. The colloidal stability of the F(ab')2-PS complexes is not only determined by the electrical charge of the complexes but also by certain properties of the protein molecules, which can be closely related to the conformational changes undergone by the F(ab')2 molecules in the adsorption process on polymer surfaces.

Adsorption↗

PubMed1993

On the structure of electrical double layer of IgG immobilized on polystyrene microspheres.

Latex particles used in the development of immunoassays usually present stability problems when the antibody is attached to the surface. This work is an attempt to know the potential distribution parameters around these complexes by electrokinetic measurements. The conversion of mobility data into zeta-potential was carried out by different theoretical approaches developed by Smoluchowski (classical equation), O'Brien and White, and Dukhin and Semenikhin. The zeta-potential calculated with allowance for electrical double layer (e.d.l.) polarization was substantially greater than zeta calculated according to the classical electrokinetic theory. The greater values of zeta D-S in comparison with zeta O-W were readily explained on the basis that in the first theory, the contribution to polarization from all ions of the diffuse layer was taken into account, whereas O'Brien and White accounted for only the ions of the hydrodynamically mobile part of the e.d.l. This is an indication that the anomalous surface conductance of latex particles coated by IgG molecules is much higher than that of bare latex particles.

Adsorption↗