LANGMUIR-BLODGETT DEPOSITED VALINOMYCIN PHOSPHOLIPID FILMS ON PLATINUM - AN AC IMPEDANCE RESPONSE TO POTASSIUM

Multilayers of phospholipid and valinomycin films are deposited onto platinum electrodes using the Langmuir-Blodgett technique. The pressure-area isotherms of the mixed lipid and valinomycin monolayers have been used to characterize the films prior to deposition. Coverage of platinum surfaces by the deposited layers is determined using an a.c. electrical impedance technique. The stability of the monolayer, lipid adhesion onto the platinum surface and the surface pressure are parameters that prove to be critical for obtaining high-impedance electrode coatings. Film deposition is carried out for high and low ionic strength subphases at neutral pH. Films deposited at surface pressures of 45 mN m-1 have an impedance on the order of that of artificial bilayer lipid membranes. The film impedance on the platinum electrodes is measured as a function of the potassium concentration. The film impedance decreases when potassium is added to the subphase. Conductance changes induced by the potassium are used to evaluate the percentage uptake of potassium by valinomycin. Mechanisms for the electrical response of the film are discussed in terms of adsorption models.