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 electrodes. The peptide was reconstituted into large unilamellar vesicles of DODAB which were fused on a negatively charged monolayer of 3-mercaptopropionic acid. The peptide forms a pore of 4 Angstrom diameter, selective for monovalent cations. The sequence of conductivity of monovalent alkaline cations is Cs+ > K+ > Na+ > Li+. The transport of these monovalent cations through this supported lipid bilayer via the gramicidin dimer was observed by a.c. impedance spectroscopy as an integral electrochemical method. Only a single bilayer preparation was necessary 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 impedance spectroscopy. The conductance of the membrane shows a linear dependence on the concentration of the cations in the bulk phase. This system is therefore recommended for biosensor devices based on ion transport through solid supported membranes. (C) 1997 Elsevier Science S.A.