ELECTROCHEMICAL OXIDATION OF AMINE-CONTAINING COMPOUNDS - A ROUTE TO THE SURFACE MODIFICATION OF GLASSY-CARBON ELECTRODES

A method for the modification of glassy carbon electrodes (GCEs) with amine-containing compounds for electrocatalytic and biosensor purposes is investigated. The method utilizes the electrooxidation of amines t o their analogous cation radicals to form a chemically stable covalent linkage between the nitrogen atom of the amine and edge plane sites a t the GCE surface. By use of X-ray photoelectron spectroscopy (XPS) fo r coverage assessment, the capability of this route is demonstrated by the immobilization of a simple primary amine at the GCE surface. An i nvestigation of the influence of substituents on the nitrogen atom (e. g., primary, secondary, tertiary amines) revealed that the surface cov erage of primary amines was approximately 3 times higher than that of secondary amines, whereas tertiary amines were not immobilized at a de tectable level. This behavior is attributed to a strong steric effect whereby bulky substituents on the nitrogen atom hinder accessibility o f the reactive amine cation radical to surface binding sites. Amine sa lts and amides also showed no detectable coverage by XPS. The utility of the method for creation of a GCE with electrocatalytic activity is demonstrated by the immobilization of dopamine (DA) at the GCE surface . The DA-modified GCE is used to facilitate oxidation of beta-NADH via a surface EC mechanism. The applicability of this method for the cons truction of biosensors that are based on biotin-avidin complexation is also demonstrated. Both of these examples illustrate the facility of this route for simplifying and shortening dramatically the processing required for immobilization using other synthetic methods. A mechanism for the immobilization process is also briefly discussed.