Numerical Calculation of the Dielectric and Electrokinetic Properties of Vesicle Suspensions

Abstract

The dielectric and electrokinetic properties of aqueous suspensions of vesicles (unilamellar liposomes) are numerically calculated in the 1 Hz to 1 GHz frequency range using a network simulation method. The model consists of a conducting internal medium surrounded by an insulating membrane with fixed surface charges on both sides. Without an applied field, the internal medium is in electric equilibrium with the external one, so that it also bears a net volume charge. Therefore, in the presence of an applied ac field, there is fluid flow both in the internal and in the external media. The obtained results are qualitatively different from those corresponding to suspensions of charged homogeneous particles, mainly due to the existence of an additional length scale (the membrane thickness) and the corresponding dispersion mechanism, charging of the membrane. Because of this dispersion, the shapes of the spectra change with the size of the particles (at constant zeta potential and particle radius to Debye length ratio) instead of merely shifting along the frequency axis. A comparison between the numerical results and those obtained using approximate analytical expressions shows deviations that are, in general, sufficiently large enough to show the necessity to use numerical results in order to interpret broad frequency range dielectric and electrokinetic measurements of vesicle suspensions.

Dielectric spectroscopy reveals nanoholes in erythrocyte ghosts

“…As described in Materials and Methods, effective complex permittivity was calculated for a suspension of cells orienting randomly. In this calculation, polarization due to mobile ions near the membrane having fixed surface charges 49,50 and a resting transmembrane potential 51 was not taken into account. This is because intact erythrocytes having fixed surface charges like ghosts do not show -dispersion and because the transmembrane potential becomes zero in ghosts whose cytoplasm is the same as the external medium.…”

Low-frequency dielectric dispersion of bacterial cell suspensions

“…Hence, the participation of the counterion polarization in the LF dispersion has been evaluated along the Dukhin and Shilove model. Grosse and Zimmerman derived an analytical solution for a more simplified model that is a sphere covered with a single shell carrying surface charges [19]. Under the circumstances, the Grosse-Zimmerman model has been adopted to examine the characteristics of the dielectric dispersion obtained for E. coli cell suspensions.…”

“…The quantities dL, L, dLh and S in Eq. (4) that have been given by Grosse and Zimmerman [19] are simplified by assuming a 1-1 electrolyte that has the same diffusion constant D for the anion and cation.…”

“…Many theoretical advances have been made along the Dukhin-Shilove model, as described in a review of Grosse and Delgado [18]. Grosse and Zimmerman [19] have extended the Dukhin-Shilove model to lipid vesicles and biological cells, which are modeled as a sphere covered with a single shell possessing charged surfaces, and have obtained an analytical solution that enables us to simulate the whole dielectric spectrum including the and the -dispersions. Further, numerical simulation has been carried out with the cell model that has a porous charged wall outside the plasma membrane [20].…”

Rapid liposome quality assessment using a lab-on-a-chip

“…27 In the context of liposome analysis, a number of recent studies have shown that electric properties of liposome suspensions and membrane coated particles can be used to study dispersion mechanisms, charging of the membrane and electrophoretic mobilities. [28][29][30][31] In our previous work we have further demonstrated that dielectric measurements provide stable and non-drifting signals due to complete sensor insulation and physical removal from the liquid sensing environment, thus eliminating bubble formations, electrode fouling and polarization events. 32,33 Since contactless measurements also significantly reduce common impedance interferences such as pH, salt and protein content variations, 34 the application of dielectric spectroscopy is ideally suited for online characterization of liposome formulations using multivariate data analysis methods.…”