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

Polyelectrolyte capsules were fabricated in aqueous media by stepwise adsor ption of polyelectrolytes onto fixed erythrocytes and subsequent template d issolution. Lipid polyelectrolyte composite capsules were prepared assembli ng lipid layers on these polyelectrolyte capsules. Dipalmitoyl phosphatidyl acid (DPPA), dipalmitoyl phosphatidyl choline (DPPC), and a mixture of bot h were used. Confocal laser scanning microscopy showed that the Lipids form a homogeneous coverage on the capsule surface. An electrorotation techniqu e was used to study the electrical properties of polyelectrolyte and lipid- polyelectrolyte composite capsules. A conductivity of 1 S/m for polyelectro lyte capsule walls was found. Lipid-polyelectrolyte composite capsules yiel ded conductivities in the range from 10(-4) to 10(-1) mS/m and capacities o f 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 blac k lipid membranes. They increased with the bulk electrolyte concentration, which was attributed to the presence of pores or defects in the lipid struc tures. The effective area of pores was estimated as 0.01% of the total caps ule surface.