An electrode assembly that may be used, for example, for electrochemically analysing a sample to determine the presence (or otherwise) of a species having biomembrane activity comprises at least one working electrode comprised of a conductive carrier substrate having a surface coated with mercury immobilised on the surface of the substrate. The surface of the mercury remote from said substrate is coated with a phospholipid layer. The preferred carrier substrate is platinum. The electrode assembly may be incorporated in a flow cell.