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R Hidalgo-Álvarez

Publications and source records attributed to R Hidalgo-Álvarez.

10 recordsLinked to original sources
PubMed2001

Colloidal stability of IgG- and IgY-coated latex microspheres.

The stabilization of antibody-latex complexes at high salt concentration is an event that cannot be explained by the widespread DLVO theory. Adsorption of antibodies on polystyrene latex usually leads to a loss in colloidal stability. However, after the expected particle aggregation induced by an increase in ionic strength, an 'anomalous' restabilization occurs when the electrolyte concentration increases even more. This non-DLVO behaviour can be explained taking into account the hydration forces, which become significant in hydrophilic surfaces. This restabilization has already been observed in different protein latex complexes. In the present work, a study on the stability patterns of polystyrene particles covered independently by mammalian and chicken antibodies has been performed. This study reveals that avian antibodies present a more hydrophobic surface than that of mammalian antibodies. In addition, it has been possible to obtain some information about the molecular orientation of the adsorbed antibodies from the stability experiments. This information has been corroborated by an immunoreactivity study.

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PubMed2001

An Experimental Test of the Ion Condensation Theory for Spherical Colloidal Particles.

This paper deals with the notion of ion condensation for spherical colloids and, more specifically, with a recent model developed to predict effective charges (Y. Levin, M. C. Barbosa, and M. N. Tamashiro, Europhys. Lett. 41, 123, 1998). Electrophoretic mobility measurements (carried out for a set of well-characterized latexes) were used to find out to what extent this theory is able to accounts for: (i) the insensitivity of mobility to surface charge, and (ii) the small values of electrokinetic charge found at low ionic strength. As the Levin theory was developed assuming no added salt, a previous discussion about the effect of additional electrolyte was needed. Contrary to what other authors have reported, our results do not support the above-mentioned theory. Copyright 2001 Academic Press.

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PubMed2000

Colloidal Interaction at the Air-Liquid Interface.

In this paper, we propose a model to analyze the stability of colloidal particles at the air-liquid interface. The proposed model for the colloidal particle interaction considers DLVO interactions and capillary, hydrophobic, and dipolar interactions between the particles. Typical values from the literature were assigned to most parameters included in the model. Numerical computation revealed the most important parameter in determining the total interaction is the density of dipoles at the external surface of the particles. We have found significant differences for the pair potential between hydrophobic and hydrophilic particles. Hydrophobic particles must aggregate in a principal minimum of the interaction potential curve while hydrophilic particles aggregate in a secondary minimum. Copyright 2000 Academic Press.

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PubMed1999

Probing Electrostatic Forces in Colloidal Suspensions through Turbidity Data.

This paper deals with the use of turbidimetry to obtain information on forces between negatively charged polymeric particles at very low ionic strength. The specific turbidity of deionized colloidal suspensions is measured and compared with the values obtained for suspensions of noninteracting particles. From these data, the integrated structure factors are experimentally obtained for several latex samples. These functions are fitted using the repulsive part of the DLVO potential, the Ornstein-Zernike equation, and the hyper-netted chain closure, which enables us to interpret the results in terms of an effective charge. The reliability of these values is discussed. In addition, a comparison between turbidimetry and light scattering data is presented. Copyright 1999 Academic Press.

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PubMed1999

The Surface Charge Density Influence on the Electrokinetic Properties of Model Colloids: Solvent Composition Effect.

This paper deals with two problems found in electrokinetics, the anomalous behavior exhibited by most polymer colloids and the discrepancy between the zeta potentials obtained from different electrokinetic phenomena. Electrophoretic mobility for dilute dispersions and streaming current for concentrated dispersions are used to determine the zeta-potential. Two systems with different features (particle radius and surface charge density) have been studied. The influence of varsigma0 on the above-mentioned problems seems to be very important. In order to test this hypothesis, different nonaqueous media were used, which were significantly different in several liquid media properties (such as bulk conductivity, dielectric constant, and viscosity) and particle properties (such as surface charge density). Copyright 1999 Academic Press.

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PubMed1998

Cluster Morphology of Protein-Coated Polymer Colloids.

We report measurements on the aggregation processes in a colloidal suspension of polystyrene particles covered with F(ab')2 (immunoglobulin IgG fragment) performed by static and dynamic light scattering. In order to study the cluster morphology of aggregates, the fractal dimension is obtained from the dependence of the scattered intensity on the scattering wave number. The stability domains of bare and protein-coated polystyrene particles were examined by plotting the stability ratio as a function of electrolyte concentration. The stability results have been explained using a modified Derjaguin-Landau-Verwey-Overbeek theory to describe the interparticle interaction. The observed change in the fractal dimension can be explained by the existence of a minimum separation distance between coagulated particles (restructuring). This minimum distance is attributed to the layer of hydrated ions and water molecules adsorbed on the particle surface. Our results are in agreement with the reversible-growth model of W. Y. Shih, I. A. Aksay, and R. Kikuchi (Phys. Rev. A. 36, 5015 (1987)) and they were supported by transmission electron microscopy observation. Copyright 1998 Academic Press.

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PubMed1998

Anomalous Colloidal Stability of Latex-Protein Systems.

An experimental study on the colloidal stability of latex-F(ab')2 and latex-IgG systems is described. The stability domains were obtained using a low-angle scattering technique to measure the rates of aggregate formation and plotting the stability ratio as a function of electrolyte concentration. The protein-coated particles present an anomalous stability at high ionic strength when the classical theory predicts aggregation. This observed deviation from DLVO behavior appears for electrolyte concentrations above some critical bulk concentration called critical stabilization concentration (csc). As we have suggested in previous publications, the existence of an additional short-range repulsive "hydration force" can explain this anomalous stability. In order to resolve more fully if this anomalous stability at high ionic strength is due to the hydration forces, the effects of pH, cation and anion type, temperature, and polyethylene glycol (a dehydrating polymer) on the experimental stability are investigated. Finally, the immunoreactivity of an anti-CRP F(ab')2-latex conjugate is studied in reaction buffers with high ionic strength. Copyright 1998 Academic Press.

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PubMed1998

Effective Charge on Polymer Colloids Obtained Using a Renormalization Model.

Static light scattering has been used to study the electrostatic interaction between colloidal particles. Experiments were carried out using a latex with a very small diameter, allowing structure determination at high particle concentration. The obtained effective charge characterizing this interaction is found to be smaller than the bare charge determined from titration. A renormalization model connecting both values has been used. The agreement between the renormalized charge and that obtained from scattering data seems to point out that this model operates well. Copyright 1998 Academic Press.

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PubMed1998

Characterization of Immunoglobulin G Bound to Latex Particles Using Surface Plasmon Resonance and Electrophoretic Mobility.

The main objective of this work was the investigation of passive adsorption and covalent coupling of a polyclonal IgG and a monoclonal preparation of IgG against HSA, to a carboxyl latex particle. The functional activity of the coupled protein was then assessed by quantitative immunoassays for the antigen. Sensitized particles, with different protein coverage, were fully characterized using a range of different technologies, including electrophoretic mobility (µe), photon correlation spectroscopy, and surface plasmon resonance (SPR). The antibody-labeled particles were studied with respect to electrokinetic behavior in pH and ionic strength titration, stability, antibody functionality, and their perfomance in immunoaggregation reactions. Important differences were observed between the two sets of particle preparations throughout the series of experiments. The differences could be attributed to the coupling of the IgG molecules to the particles by the two different adsorption protocols. When proteins were chemically bound to the polymer surface it was necessary to activate the carboxyl groups with a carbodiimide (CDI) moiety that in our case was positively charged. The differences in characteristics between the adsorbed and the coupled antibody particles are thought to be due to the fact that in the covalent coupling protocol some CDI molecules remained linked to the particles, which altered the average electrical state of the outer layer in comparison with those samples where antibodies were physically adsorbed. On the other hand, the isoelectric point of the monoclonal antibody was lower (5.4 +/- 0.1) than the pI of the polyclonal antisera (6.9 +/- 0.9), which could explain why the IgG-latex complexes created with monoclonal molecules were colloidally more stable at neutral pH than those created with the polyclonal antisera. However, no immunoaggregation of antibody particles by the presence of antigen was found with the former. The use of SPR demonstrated that the equilibrium constants for the antibody-antigen recognition of the two antibody preparations were quite similar (KA polyclonal IgG = 2.8 10(8) M-1; KA monoclonal IgG = 9.5 10(7) M-1). These observations suggest that the lack of aggregation mediated by antigen demonstrated by the monoclonal antibody coupled to the latex particles may be due to this protein recognizing only one epitope in the HSA molecule. However, as the repulsive charge between antibody-latex particles counteracts the attractive forces between the antigen epitope and the antibody paratope, the greatest immunoaggregation was obtained when using latex particle-antibody complex with a low charge density (N) in the external layer. Copyright 1998 Academic Press.

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