IMPEDANCE SPECTROSCOPY OF PORIN AND GRAMICIDIN PORES RECONSTITUTED INTO SUPPORTED LIPID BILAYERS ON INDIUM-TIN-OXIDE ELECTRODES

We prepared electrolyte-membrane-electrolyte-semiconductor (EMES) inte rfaces 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 indiu m-tin-oxide (ITO) semiconductor electrodes. Membrane resistances of up to 109 k Omega cm(2) were reached. By conductivity measurements in th e presence of the redox couple K3Fe(CN)(6)/K4Fe(CN)(6) the area fracti on of defects exhibited in the supported membranes was determined to b e less than 0.0001. We show that by measurement of the impedance over a large frequency range (10(-1)-10(5) Hz) it is possible to discrimina te between changes (1) of the capacitance of the ITO electrodes, (2) t he membrane capacitance, and (3) the membrane conductivity of the sens or device. The membrane pore gramicidin and the outer membrane protein s 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 mea suring the membrane resistance in the presence of pores for various el ectrolyte compositions.