Tethered mono- and bilayer lipid membranes on Au and Hg

A simple thiolipid molecule was synthesized by covalent linking of mercaptopropionic acid with phosphatidylethanolamine. The integrity of thiolipid self-assembled monolayers supported on gold and mercury electrodes was tested by electrochemical techniques both in the absence and in the presence of hydrophilic redox couples. The organization of the thiolipid monolayer supported on gold was also assessed by surface-enhanced Raman spectroscopy both in air and in aqueous solution. The thiolipid nonolayer was then covered with a phospholipid monolayer to form a bilayer lipid membrane tethered to the electrode surface (t-BLM), and the electrochemical tests were repeated using cyclic voltammetry, differential capacitance, impedance spectroscopy (IS), and chronocoulometry. These bilayers possess an exceptionally good mechanical stability while exhibiting electrochemical properties similar to those of conventional BLMs. However, no substantial "ionic reservoir" separating the t-BLM from the electrode surface was observed by IS. Most probably, this is due to the insufficient length of the mercaptopropionic spacer and its gauche conformation related to the electrode surface.