Phospholipid bilayers at the mercury (Hg)/water interface

Abstract

This study reports on the electrochemical characterisation of dioleoyl phospatidylcholine (DOPC) bilayer structures on a negatively polarised mercury (Hg) electrode. The bilayers are stable on the Hg surface between −1.0 and −1.3 V applied potential. The experimental approaches were:- (i) rapid cyclic voltammetry (RCV) to “fingerprint” the bilayers, (ii) potential step experiments to record Zn2+ reduction and, (iii) electrochemical impedance. The results show the following. Both the specific capacitance (5 μF cm−2) and the specific resistance of the bilayer are higher and lower respectively than that of a defect-free free standing DOPC bilayer. This indicates the presence of water and ions in the bilayer within an applied negative field. The bilayer's resistance to electrolyte movement decreases with increase in negative potential to a minimum at −1.3 V. The DOPC bilayer is less permeable to Zn2+ ions compared to the DOPC monolayer coated electrode at applied negative potentials and its permeability to Zn2+ increases with an increase in negative applied potential. The specific capacitance of the bilayer increases to about 7.5 μF cm−2 with increase in applied negative potential showing the increasing significance of water in the bilayer commensurate with its increased permeability to ions. Adsorption of SiO2 nanoparticles on the bilayer surface causes a step negative potential shift in the anodic capacitance current bilayer reformation peak indicating an acceleration of the bilayer reformation process.