Cyclic voltammetry and ac impedance studies of Ca2+-induced ion channels on Pt-BLM

Self-assembled phosphatidylcholine/cholesterol bilayer lipid membrane (BLM) was fabricated on Pt electrode, which bad been cleaned by high power ultrasonic horn. The influence of Ca2+ ions on the electron transfer of Fe(CN)(6)(3-/4-) couple on Pt supported BLM (Pt-BLM) was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CV experiments showed directly that Ca2+ ions could induce electron transfer on Pt-BLM. Three possibilities of the cause of redox reaction induced by Ca2+ ions were discussed: (1) electronic tunneling across bilayer, (2) electronic tunneling across monolayer, (3) direct electron transfer between Fe(CN)(6)(3-/4-) ions and Pt electrode through Ca2+ induced ion-channels. Results of calculations based on Marcus's theory indicate that electronic tunneling across bilayer and monolayer contributes little to the redox current. The theory of partially blocked electrode was employed to analyze the sigmoidal CV curves, and it was concluded that ion-channels generated by Ca2+ ions were the main cause of electron transfer reaction on Pt-BLM. EIS measurement showed that Pt-BLM became porous after Ca2+ ions were added to the electrolyte. This was consistent with the conclusion drawn from CV experiments. Since ion-channels play the role similar to micro defects, it is concluded from CV and EIS experiments that sigmoidal CV curves and depressed circular arcs are evidence for the existence of micro defects on unmodified solid-supported-BLM. (C) 1998 Elsevier Science S.A. All rights reserved.