Impedance spectroscopy of porin and gramicidin pores reconstituted into supported lipid bilayers on indium-tin-oxide electrodes

We prepared electrolyte-membrane-electrolyte-semiconductor (EMES) interfaces by fusion and high-temperature annealing of positively charged lipid vesicles (containing 49 mol % cholesterol and 42 mol % lecithin besides 9 mol % positively charged lipid) on optical transparent indium-tin-oxide (ITO) semiconductor electrodes. Membrane resistances of up to 109 kΩ cm² were reached. By conductivity measurements in the presence of the redox couple K₃Fe(CN)₆/K₄Fe(CN)₆ the area fraction of defects exhibited in the supported membranes was determined to be less than 0.0001. We show that by measurement of the impedance over a large frequency range (10^-1-10⁵ Hz) it is possible to discriminate between changes (1) of the capacitance of the ITO electrodes, (2) the membrane capacitance, and (3) the membrane conductivity of the sensor device. The membrane pore gramicidin and the outer membrane proteins OmpF and OmpA (from E. coli) where reconstituted into the supported membranes by transfer from vesicles. The functionality and selectivity of gramicidin and OmpF in supported membranes are demonstrated by measuring the membrane resistance in the presence of pores for various electrolyte compositions.