Conductance and capacitance of polyelectrolyte and lipid-polyelectrolyte composite capsules as measured by electrorotation

Polyelectrolyte capsules were fabricated in aqueous media by stepwise adsorption of polyelectrolytes onto fixed erythrocytes and subsequent template dissolution. Lipid polyelectrolyte composite capsules were prepared assembling lipid layers on these polyelectrolyte capsules. Dipalmitoyl phosphatidyl acid (DPPA), dipalmitoyl phosphatidyl choline (DPPC), and a mixture of both were used. Confocal laser scanning microscopy showed that the Lipids form a homogeneous coverage on the capsule surface. An electrorotation technique was used to study the electrical properties of polyelectrolyte and lipid-polyelectrolyte composite capsules. A conductivity of 1 S/m for polyelectrolyte capsule walls was found. Lipid-polyelectrolyte composite capsules yielded conductivities in the range from 10(-4) to 10(-1) mS/m and capacities of 2.7 mu F/cm(2) for DPPA and 0.5 mu F/cm(2) for DPPC. These conductivities of lipid-polyelectrolyte composite capsules were much higher than for black lipid membranes. They increased with the bulk electrolyte concentration, which was attributed to the presence of pores or defects in the lipid structures. The effective area of pores was estimated as 0.01% of the total capsule surface.