1991 Volume 7 Issue 6 Pages 853-862
The potentiometric behavior of valinomycin incorporated bilayer lipid membranes (BLMs) was studied in view of a comparison with its solvent polymeric membrane counterpart. The preparation of membranes has greatly relied on the Takagi-Montal method as well as synthetic lipid chemistry. The prepared membrane was first characterized regarding its electrical resistance, electrical capacitance and the effect of gramicidin to reveal its Bilayer nature. The membrane potential was systematically studied in terms of i) the valinomycin concentration in the lipid membrane and ii) the effect of the lipid charge. The observed membrane potentials were compared with those of valinomycin-incorporated solvent polymeric membranes in terms of i) the detection limit, ii) the dynamic range and iii) the selectivity for alkali metal ions. It was found that the detection limit, dynamic range and optimum valinomycin concentration for the K+ ion-induced Nernstian response for the BLM electrode were comparable to those of the solvent polymeric membranes. The selectivity coefficients (Kpotij) for alkali metal ions determined by the separate solution method were also comparable to those of liquid membranes. However, a marked difference between both the membranes was found with respect to the effect of the membranous charge. The potentiometric response of the BLMs was found to depend on the charges of lipids. With negatively charged BLMs, the detection limit and dynamic range for K+ ions were improved. On the contrary, the response with positively charged BLMs was significantly reduced without any change in the Nernstian slope. This effect of lipid charge was compared with the anion effect for a solvent polymeric membrane. Finally, the first successful formation of planar BLMs using totally synthetic lipids was also demonstrated.
