IMPEDANCE ANALYSIS OF ION-TRANSPORT THROUGH GRAMICIDIN CHANNELS INCORPORATED IN SOLID SUPPORTED LIPID BILAYERS

The topic of this study is a solid supported lipid bilayer consisting of dimethyldioctadecylammoniumbromide (DODAB) and the channel-forming polypeptide, gramicidin D, from Bacillus brevis immobilized on gold el ectrodes. The peptide was reconstituted into large unilamellar vesicle s of DODAB which were fused on a negatively charged monolayer of 3-mer captopropionic acid. The peptide forms a pore of 4 Angstrom diameter, selective for monovalent cations. The sequence of conductivity of mono valent alkaline cations is Cs+ > K+ > Na+ > Li+. The transport of thes e monovalent cations through this supported lipid bilayer via the gram icidin dimer was observed by a.c. impedance spectroscopy as an integra l electrochemical method. Only a single bilayer preparation was necess ary to perform the whole measurement. The obtained data were analysed with an equivalent circuit based on the theory developed by de Levie. We succeeded in confirming the sequence of the conductivity by impedan ce spectroscopy. The conductance of the membrane shows a linear depend ence on the concentration of the cations in the bulk phase. This syste m is therefore recommended for biosensor devices based on ion transpor t through solid supported membranes. (C) 1997 Elsevier Science S.A.