Changes in the structure of model biological membranes in the presence of perfluorooctanesulphonic acid – Electrochemical and EC-STM study

The changes caused by the presence of perfluorooctanesulphonic acid (PFOS) in the structure and electrochemical characteristics of model biological membranes composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) supported on gold electrodes were examined using electrochemical techniques and electrochemical scanning tunneling microscopy. Phospholipid mono and bilayers were prepared using the Langmuir–Blodgett (LB) technique alone or combined with of the Langmuir–Schaefer (LB/LS) techniques. Square wave voltammetry was employed to monitor the incorporation of PFOS into already existing model membranes. The accessibility of potassium ferrocyanides to the electrode surface depended on the time of contact of the bilayer with PFOS solutions. Electrostatic attraction between PFOS present in the model membrane and positively charged probes resulted in the adsorption of the probe on the lipid membrane modified electrode. Even highly soluble species, i.e. hexaamineruthenium complex revealed adsorption on the gold electrodes modified with DMPC bilayers containing PFOS. The presence of PFOS in model biological membranes was visualized by means of electrochemical scanning tunneling microscopy (EC-STM). Topographically higher PFOS-enriched domains were clearly distinguishable among lower pure DMPC regions.