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A Di Biasio

Publications and source records attributed to A Di Biasio.

8 recordsLinked to original sources
PubMed2006

Dielectric properties of aqueous zwitterionic liposome suspensions.

The dielectric spectra of aqueous suspensions of unilamellar liposomial vesicles built up by zwitterionic phospholipids (dipalmitoylphosphatidyl-choline, DPPC) were measured over the frequency range extending from 1 kHz to 10 MHz, where the interfacial polarization effects, due to the highly heterogeneous properties of the system, prevail. The dielectric parameters, i.e., the permittivity epsilon'(omega) and the electrical conductivity sigma(omega), have been analyzed in terms of dielectric models based on the effective medium approximation theory, considering the contribution associated with the bulk ion diffusion on both sides of the aqueous interfaces. The zwitterionic character of the lipidic bilayer has been modeled by introducing an "apparent" surface charge density at both the inner and outer aqueous interface, which causes a tangential ion diffusion similar to the one occurring in charged colloidal particle suspensions. A good agreement with the experimental results has been found for all the liposomes investigated, with size ranging from 100 to 1000 nm in diameter, and the most relevant parameters have briefly discussed in the light of the effective medium approximation theory.

Colloids↗
PubMed2005

Effect of the shape of human erythrocytes on the evaluation of the passive electrical properties of the cell membrane.

The possible influence of the cell shape on the derivation of the passive electrical parameters of a biological cell membrane is discussed in light of two different models which describe the cell as a shelled ellipsoidal particle and as a biconcave disk obtained by the revolution of the Cassini oval, respectively. Whereas within the first model, the Laplace equation can be solved analytically, in the second one a numerical algorithm based on the boundary element method has been employed. We have compared the results obtained by these two different models in the case of normal human erythrocyte cell membrane, using radiowave dielectric spectroscopy measurements. Our findings show that, although in principle the cell shape might deeply affect the evaluation of the passive electrical parameters of the cell membrane, in the case of the erythrocyte shape modelled by the Cassini curve, only small deviations are evidenced in comparison to the values derived, as usually done in the dielectric spectroscopy of biological cell suspensions, from an ellipsoidal model analysis. This result gives further support to the reliability of the data reported in the literature based on an ellipsoidal shape erythrocyte model.

Cell Shape↗
PubMed2000

Quasi-elastic light scattering from large anisotropic particles: application to the red blood cells.

The usefulness of dynamic light scattering measurements for the determination of particle size and shape in suspensions of biological objects is well established. However, when the particle sizes are larger than the wavelength of the incident light, so that structural information on the scattering particles can be made available, the analysis of the correlation function of the scattered light requires a careful examination, owing to the problem involved in its theoretical description. In this note, dynamic light scattering techniques were employed for the determination of the size of human normal erythrocytes in physiological saline solution (isotonic solution) with the aim to discuss in detail the different effects that contribute to the scattered light intensity distribution and to evidentiate how correct information can be made available only when the anisotropic contribution to the translational diffusion coefficient of the erythrocyte cells is properly taken into account. In the case of erythrocytes, this effect produces deviation of the order of 8-10% in the evaluation of the cell size (the cell diameter and cell thickness) that can be accounted for by an appropriate dependence upon time of the autocorrelation function. Once the electric field autocorrelation function, where the intraparticle correlation function contains the correction for the anisotropic contribution, is considered, reasonable agreement was obtained between the data deduced from light scattering methods and those from scanning electron microscope pictures.

Animals↗
PubMed1990

Determination of cell membrane passive electrical properties using frequency domain dielectric spectroscopy technique. A new approach.

To take into account the highly irregular surface morphology of cell membranes we have analyzed impedance measurements of biological cell suspensions in general terms using a fractal description of the surface roughness of the cell membrane. This analysis has been applied to human erythrocytes in different solutions of alkaline metal salts and to human lymphocytes, since these cells present a different surface irregularity. The passive electrical properties (dielectric constant and electrical conductivity) deduced from conductivity measurements at radiowave frequencies have been discussed on the basis of the fractal dimension of the membrane surface.

Cell Membrane↗
PubMed1984

Effect of ions on counterion fluctuation in low-molecular weight DNA dielectric dispersions.

The dielectric permittivity of aqueous solutions of low-molecular weight DNA (Mr = 3.2 X 10(5) ) in the presence of MgCl2 and AgNO3 has been measured in the frequency range from 5 kHz to 30 MHz, at a temperature of 25 degrees C. The DNA concentration was 3.5 X 10(-4) M in terms of phosphate and the salt concentration was varied from 1 X 10(-5) to 2 X 10(-4) M. The dielectric results have been analyzed in terms of two contiguous dielectric dispersions, and characteristic parameters have been discussed on the basis of polyelectrolyte theories which deal with counterion fluctuation. Some molecular parameters of the DNA molecule in electrolyte solutions are estimated.

Animals↗