ION-SELECTIVE MONOLAYER MEMBRANES BASED UPON SELF-ASSEMBLING TETRADENTATE LIGAND MONOLAYERS ON GOLD ELECTRODES .3. APPLICATION AS SELECTIVE ION SENSORS

Gold electrodes coated with mixed monolayer membranes comprising 2,2'-thiobis(ethyl acetoacetate) (TBEA) and n-octadecyltrichlorosilane (OTS) respond selectively to certain divalent ions (i.e. Cu2+, Pb2+) while completely blocking the electrochemical response of other ions (e.g. Fe2+). This unique property is exploited for demonstrating the feasibility of using self-assembling monolayers for electroanalytical sensing. Hence, a direct voltammetric scheme is described for the determination of Cu2+ and Pb2+ ions at an Au/(TBEA + OTS) electrode, and an indirect scheme is shown for the determination of Zn2+ ions. In all cases, the presence of a large excess of Fe2+ ions has no effect on the analysis. The potential application of such monolayer systems as sensor elements in future molecular-size technology is emphasized.